Sodium-ion battery negative electrode material and preparation method and application thereof

Abstract

This invention relates to a sodium-ion battery anode material, its preparation method, and its application. It addresses the technical problems of poor cycle stability and low rate capability of existing selenide electrodes. The sodium-ion battery anode material of this invention is a self-supporting cobalt-tin selenide nanowire array with a heterogeneous structure grown on carbon cloth. Preparation method: Cobalt source, tin source, alkali source, and additives are added to a solvent, mixed evenly, and then transferred to a reaction vessel. Pretreated carbon cloth is then vertically placed in the mixture. After a solvothermal reaction, selenization is performed in a tube furnace to obtain the anode material. This material exhibits excellent sodium storage characteristics at a current density of 0.1 Ag. ‑1 After 100 cycles at the current density, the capacity remained at 885.4 mAh g. ‑1 It boasts a capacity retention rate of up to 98.6%, and its manufacturing process is simple, with readily available raw materials and low cost, making it suitable for use in the sodium-ion battery field.

Description

Technical Field

[0001] This invention relates to sodium-ion battery anode sheets, their preparation methods, and applications, belonging to the field of sodium-ion battery anode materials. Background Technology

[0002] Sodium-ion batteries share similar working principles and electrochemical performance with lithium-ion batteries, and sodium resources are abundant and inexpensive, attracting widespread attention from researchers. However, due to the limited availability and low price of sodium... + The radius is larger than Li + The large radius of the electrode material leads to slow sodium storage reaction kinetics and large volume expansion, which in turn limits the rate performance and cycle performance of sodium-ion batteries. Therefore, it is imperative to develop new materials with both high specific capacity and excellent stability as anode materials for sodium-ion batteries.

[0003] In recent years, transition metal selenide compounds such as FeSe2, NiSe2, MoSe2, CoSe2, SnSe2, and ZnSe have been widely used in energy storage due to their excellent physicochemical properties, high theoretical specific capacity, and simple synthesis methods. Among them, tin-based compounds are considered promising anode materials for sodium-ion batteries because, compared with other metal selenides, they have weaker ionic bonds and larger insertion / extraction distances, which are conducive to electrochemical conversion reactions. However, tin selenides experience severe volume expansion during sodium ion insertion and extraction, leading to pulverization and a significant reduction in rate performance and cycle stability. To effectively improve the rate performance and cycle stability of tin selenide electrode materials, introducing a relatively stable metal element to form a heterostructure can alleviate the problems of volume expansion and poor conductivity. Bimetallic selenide heterostructures, in particular, generate interfacial effects due to the synergistic effect between different metal ions, and produce built-in electric fields at different interfaces to achieve unique electron transfer, thereby improving the sodium ion storage capacity of the electrode material. For example, the article "SnSe2 / FeSe2 Nanocubes Capsulated in Nitrogen Doped Carbon Realizing Stable Sodium-Ion Storage at Ultrahigh Rate," published in *Small Methods*, Volume 5, Issue 9, 2021, prepared carbon-coated SnSe2 / FeSe2 cubes at a current density of 0.2 Ag. -1 After 70 cycles, its specific capacity still reaches 545.3 mAh g. -1The article "Heterostructure SnSe2 / ZnSe@PDA nanobox for Stable and Highly Efficient Sodium-Ion Storag," published in Volume 10, Issue 24 of *Advanced Energy Materials* in 2020, describes the synthesis of SnSe2 / ZnSe@PDA nanoboxes. These nanoboxes, when used as anodes in sodium-ion batteries, exhibit excellent sodium storage characteristics at high current densities (4 Ag). -1 Even at this temperature, its specific capacity can still reach 253.3 mAh g. -1 However, technical problems such as poor cycle stability and low rate capability still exist due to the ease of structural collapse. Summary of the Invention

[0004] The present invention aims to solve the technical problems of poor cycle stability and low rate performance of existing selenide electrodes, and provides a sodium-ion battery anode material, its preparation method and application.

[0005] The sodium-ion battery anode material of the present invention is formed by in-situ growth of self-supported cobalt-tin-selenide nanowires on carbon cloth to form a one-dimensional nanowire array; the cobalt-tin-selenide nanowires are composed of CoSe2-SnSe2 heterojunctions. This anode material uses self-supported cobalt-tin-selenide nanowires as the active material, eliminating the need for additional conductive agents and binders, and exhibits good conductivity and stability.

[0006] Furthermore, the cobalt-tin-selenide nanowires described herein have a diameter of 50–150 nm and an aspect ratio of 5–40. The aspect ratio of these one-dimensional nanowires is controllable, exhibiting a unique heterostructure. One-dimensional nanowires with specific aspect ratios can provide shorter diffusion paths for electrons / ions, resulting in higher transport efficiency. The interactive coupling between the heterogeneous metal regions produces a synergistic effect, effectively improving the charge transfer capability at the interface and promoting the rapid diffusion of sodium ions. This solves the technical problems of poor cycle stability and low rate performance caused by the easy pulverization and collapse of the anode material.

[0007] The above-mentioned method for preparing sodium-ion battery anode materials is carried out according to the following steps:

[0008] 1. Pre-treat the carbon cloth;

[0009] 2. Weigh out the cobalt source, tin source, alkali source, and additive according to the molar ratio of cobalt source, tin source, alkali source, and additive as (0.3~5):1:(1.7~20):(1.7~20), add them to the solvent, and sonicate them while stirring to fully dissolve them to obtain a mixture.

[0010] 3. Transfer the mixture obtained in step 2 to the reactor, then vertically place the pretreated carbon cloth into the reactor, heat it to carry out a solvothermal reaction at a temperature of 100-150℃ for 5-24 hours, and cool it to room temperature to obtain the precursor.

[0011] Fourth, the precursor obtained in step three is placed downstream of a quartz tube in a tubular furnace, and a selenium source is placed upstream of the quartz tube. Under the protection of a protective gas, the temperature is raised to 300–600°C at a rate of 1–10°C / min and maintained for 1–6 hours for selenization treatment. During the selenization treatment, the flow rate of the protective gas is maintained at 60–1000 mL / min. The mixture is then naturally cooled to room temperature to obtain the sodium-ion battery anode material. It is a self-supporting cobalt-tin-selenide nanowire array with a heterostructure grown on carbon cloth.

[0012] Furthermore, the carbon cloth pretreatment described in step one involves: first, ultrasonically cleaning the carbon cloth sequentially in acetone, concentrated nitric acid (63% by mass), concentrated sulfuric acid (98% by mass), ethanol, and deionized water for 5–30 minutes each; then, drying it in a forced-air drying oven at 40–80°C for 4–8 hours to obtain clean carbon cloth. This pretreatment removes organic matter and oxide film from the carbon cloth.

[0013] Furthermore, the cobalt source mentioned in step two is one or more of cobalt nitrate, cobalt chloride, cobalt acetate tetrahydrate, and cobalt hydroxide.

[0014] Furthermore, the tin source mentioned in step two is one or more of stannous chloride, tin oxide, and tin sulfide.

[0015] Furthermore, the alkaline source mentioned in step two is one or more of urea, ammonia water with a mass percentage concentration of 25%, sodium hydroxide, and potassium hydroxide.

[0016] Furthermore, the additive mentioned in step two is one or more of sodium citrate, ammonium fluoride, and hexamethylenetetramine.

[0017] Furthermore, the solvent mentioned in step two is one or more of water, methanol, ethanol, ethylene glycol, and dimethylformamide.

[0018] Furthermore, the molar ratio of the cobalt source, tin source, alkali source, and additives mentioned in step two is (1-4):1:(3-10):(3-10).

[0019] Furthermore, the selenium source mentioned in step four is selenium powder, selenium dioxide, or sodium selenite.

[0020] Furthermore, the protective gas mentioned in step four is nitrogen, argon, helium, or a mixture of hydrogen and argon.

[0021] Furthermore, the selenization treatment described in step four involves heating to 400–500°C at a rate of 1–8°C / min and holding for 2–5 hours.

[0022] The aforementioned application of sodium-ion battery negative electrode sheets involves using them as the negative electrode of a sodium-ion battery, enabling the sodium-ion battery to simultaneously possess excellent rate performance and cycle performance.

[0023] This invention utilizes a mixed solution containing cobalt, tin, alkali, and additives to synthesize a self-supporting bimetallic CoSe2-SnSe2 heterojunction nanowire array in situ on carbon cloth via solvothermal and controlled selenization treatment. This array exhibits high specific surface area, ample exposure of active sites, and excellent assembly performance, providing shorter and more efficient diffusion paths for electrons / ions. The addition and ratio of the alkali and additives are key factors in obtaining the one-dimensional nanowire structure. By controlling the concentration of anions in the alkaline system to induce the generation of metal ions and promote their unidirectional growth, combined with appropriate solvothermal reaction conditions, a bimetallic heterojunction structure is formed. Controlled selenization treatment then endows the electrode material with advantages in interfacial charge transport, enhancing electrochemical reaction kinetics and facilitating rapid sodium ion diffusion, resulting in excellent electrochemical rate performance. The strong interaction between cobalt and tin enhances the local electronic states of tin atoms, thereby widening the metal lattice spacing and lowering the diffusion barrier. This strengthens the electrolyte's slow-release effect, thus improving the electrochemical stability of the electrode material. Furthermore, the in-situ growth of the electrode material on pretreated carbon cloth ensures a tight and robust bond between the CoSe2-SnSe2 heterojunction nanowire array and the current collector, effectively preventing further stacking and collapse of the one-dimensional nanowires during electrochemical reactions, further improving its cycle stability and rate performance. Therefore, when the self-supported bimetallic CoSe2-SnSe2 heterojunction nanowire array is used as the anode in a sodium-ion battery, it exhibits excellent sodium storage characteristics at a current density of 0.1 Ag. -1 After 100 cycles at the current density, the capacity remained at 885.4 mAh g. -1 It boasts a capacity retention rate as high as 98.6%. Moreover, the material's preparation process is simple, the raw materials are readily available, and the cost is low, making it suitable for use in sodium-ion batteries. Attached Figure Description

[0024] Figure 1 This is a low-magnification SEM image of the sodium-ion battery anode material prepared in Example 1;

[0025] Figure 2 These are high-magnification SEM images of the sodium-ion battery anode material prepared in Example 1;

[0026] Figure 3This is the XRD pattern of the sodium-ion battery anode material prepared in Example 1;

[0027] Figure 4 These are TEM and HRTEM images and mapping diagrams of the sodium-ion battery anode material prepared in Example 1, including elemental distribution diagrams of Sn, Co, and Se.

[0028] Figure 5 The graph shows the rate performance of the sodium-ion battery anode material prepared in Example 1 and its performance at 0.1 Ag. -1 The following is a performance graph for 100 cycles;

[0029] Figure 6 These are SEM images of the samples prepared in Examples 1-8;

[0030] Figure 7 These are SEM images of the samples prepared in Comparative Examples 1 to 8. Detailed Implementation

[0031] The beneficial effects of the present invention will be verified using the following examples.

[0032] Example 1: The preparation method of the sodium-ion battery negative electrode material in this example is carried out according to the following steps:

[0033] I. Carbon cloth pretreatment: First, carbon cloth cut to size 3.5cm×4cm was ultrasonically cleaned in sequence in 50mL acetone, 200mL concentrated nitric acid with a mass concentration of 63%, 200mL concentrated sulfuric acid with a mass concentration of 98%, 50mL ethanol, and 50mL deionized water for 15min each; then it was placed in a forced-air drying oven and dried at 40℃ for 6h to obtain clean carbon cloth. This pretreatment removed organic matter and oxide film from the surface of the carbon cloth.

[0034] 2. Weigh 0.873 g of cobalt nitrate, 0.226 g of stannous chloride dihydrate, 0.36 g of urea, and 0.222 g of ammonium fluoride and add them to 60 mL of methanol. Stir and sonicate to dissolve them completely to obtain a mixture.

[0035] 3. Transfer the mixture obtained in step 2 to the reactor, then vertically place the pretreated carbon cloth into the reactor, and then place the reactor in an oven at 120°C for 12 hours to carry out a solvothermal reaction. After cooling to room temperature, the precursor is obtained.

[0036] 4. Place the precursor obtained in step 3 downstream of the quartz tube of the tubular furnace, and place selenium powder upstream of the quartz tube. The mass of the selenium powder is twice the mass of the precursor. Under the protection of argon, heat to 400℃ at a rate of 2-10℃ / min and hold for 3 hours for selenization treatment. The flow rate of argon is maintained at 100mL / min during the selenization treatment. After the selenization treatment is completed, cool naturally to room temperature to obtain a carbon cloth self-supported CoSe2-SnSe2 heterojunction nanowire array; named CoSe2 / SnSe2@CC nanowire array.

[0037] Scanning electron microscope (SEM) images of the CoSe2 / SnSe2@CC nanowire array prepared in Example 1 are shown below. Figure 1 and Figure 2 As shown in the figure, the bimetallic cobalt-tin selenide one-dimensional nanowires are uniformly grown in situ on the carbon cloth and are tightly bonded to the carbon cloth. The in-situ grown one-dimensional nanowires have a diameter of about 100 nm, a length of about 2 μm, and an aspect ratio of 20:1. The one-dimensional nanowires are intertwined with each other. This structure can effectively improve the electrochemical specific surface area of ​​the material and provide effective space to alleviate volume expansion.

[0038] Figure 3 The XRD pattern of the CoSe2 / SnSe2@CC nanowire array prepared in Example 1 is shown in the figure. As shown, there are obvious diffraction peaks at 14.4°, 30.6°, 40.0°, 47.6°, 50.1° and 78.4°, corresponding to the (001), (101), (102), (110), (111) and (211) crystal planes of SnSe2; the characteristic peaks at 34.2°, 37.6°, 43.7°, 51.7°, 56.5°, 58.8° and 73.9° correspond to the (210), (211), (220), (311), (230), (321) and (421) crystal planes of CoSe2, respectively. It can be seen that the prepared CoSe2 / SnSe2@CC nanowire array contains both SnSe2 and CoSe2 phases and forms a heterojunction structure.

[0039] Figure 4 TEM and HRTEM images and mapping diagrams of the CoSe2 / SnSe2@CC nanowire array prepared in Example 1. TEM images ( Figure 4 a and Figure 4 b) shows that CoSe2 / SnSe2@CC is a one-dimensional nanowire structure with an average nanowire diameter of 100 nm. HRTEM image ( Figure 4c) shows two types of lattice fringes with interplanar spacings of 0.20 nm and 0.08 nm, corresponding to the (112) plane of CoSe2 and the (001) plane of SnSe2, respectively. These two types of lattice fringes have a clear interface and are in close contact, demonstrating that the CoSe2 / SnSe2@CC nanowire array has a heterostructure. All these conclusions are consistent with the XRD characterization results. Furthermore, from the mapping diagram ( Figure 4 In d), it can be clearly seen that the three elements Sn, Co and Se are uniformly distributed in the one-dimensional nanowire.

[0040] The CoSe2 / SnSe2@CC nanowire array prepared in Example 1 was cut into circular electrodes with a diameter of 1 cm. These electrodes were then placed in a vacuum drying oven and kept at 120°C for 12 hours to remove moisture and oxygen. They were then transferred to an MBRAUN UNLAB SP 10638 glove box (McRaun GmbH, Germany). The battery assembly and sodium block cutting processes were both carried out in the glove box, ensuring that the water and oxygen content remained below 0.1 ppm throughout the process. The assembly process was as follows: A clean positive electrode shell was taken, a gasket was placed inside, and a 1 mm thick sodium sheet was placed on the gasket. Electrolyte (1.0 mol / L NaClO4 / [V(ethylene carbonate):V(diethyl carbonate) = 1:1]) was added. Then, the separator, the prepared negative electrode sheet, the gasket, and the spring sheet were placed inside. Finally, the negative electrode shell was covered, and the battery was heat-pressed to obtain the battery. The battery was kept at a constant temperature of 25°C for 24 hours, and then electrochemical tests were performed.

[0041] Rate performance tests were conducted on the battery using the CoSe2 / SnSe2@CC nanowire array prepared in Example 1 as the anode material for a sodium-ion battery to evaluate the sodium storage characteristics of the CoSe2 / SnSe2@CC nanowire array. The rate performance graphs are shown below. Figure 5 And as shown in Table 1. Among them, Figure 5 Figure 'a' shows the rate performance diagram. As the current density increases, the specific capacity of the electrode material does not show a significant decrease. At a current density of 0.1 Ag... -1 Below, the capacity can reach 897.5mAhg -1 When the current density continues to increase to 5.0 Ag -1 Afterwards, its specific capacity can reach 611.4 mAh g. -1 Meanwhile, when the current density returns to 0.1 Ag... -1 At that time, the specific capacity of the electrode material can still reach 882.3 mAh g. -1 The specific capacity decreased slightly compared to the initial value, which confirms that the CoSe2 / SnSe2@CC nanowire array has excellent rate performance. Figure 5b is in 0.1Ag -1 The following is a performance graph for 100 cycles, from Figure 5 As can be clearly seen in Table 1, at 0.1 Ag -1 After 100 cycles, the sample prepared in Example 1 still had 885.4 mAh g⁻¹. -1 The high specific capacity and capacity retention of 98.6% further confirm that the CoSe2 / SnSe2@CC nanowire array prepared in Example 1 possesses both high rate capability and cycling stability. This is mainly due to the synergistic effect of the self-supporting structure, heterojunction structure, and one-dimensional nanowire morphology of the CoSe2 / SnSe2@CC nanowire array, which allows the properties of CoSe2-SnSe2 to be fully utilized.

[0042] Example 2: This example differs from Example 1 in that in step two, 0.873 g of cobalt nitrate, 0.451 g of stannous chloride dihydrate, 0.721 g of urea, and 0.444 g of ammonium fluoride are weighed and added to 60 mL of methanol. The other steps and parameters are the same as in Example 1.

[0043] Example 3: This example differs from Example 1 in that the solvothermal reaction temperature in step three is 150°C and the time is 5 hours. The other steps and parameters are the same as in Example 1.

[0044] Example 4: This example differs from Example 1 in that the temperature of the solvothermal reaction in step three is 100°C and the time is 24 hours. The other steps and parameters are the same as in Example 1.

[0045] Example 5: This example differs from Example 1 in that the selenization temperature in step four is 400℃ and the selenization time is 5 hours. The other steps and parameters are the same as in Example 1.

[0046] Example 6: This example differs from Example 1 in that the selenization temperature in step four is 600°C and the selenization time is 1 hour. The other steps and parameters are the same as in Example 1.

[0047] The CoSe2 / SnSe2@CC nanowire arrays prepared in Examples 2-6 are as follows: Figure 6 As shown in a~e, from Figure 6 As can be seen from the examples, CoSe2 / SnSe2@CC nanowire arrays were obtained in Examples 2-6. In these arrays, CoSe2-SnSe2 one-dimensional nanowires were uniformly distributed on the carbon cloth, forming a mesh array structure. Electrochemical performance tests were conducted on these nanowires as anode materials for sodium-ion batteries. Under different current densities and cycling tests, they exhibited good rate performance and excellent electrochemical stability, as detailed in Table 1.

[0048] Comparative Example 1: This comparative example differs from Example 1 in that it does not have a carbon cloth pretreatment process; the other steps and parameters are the same as in Example 1.

[0049] Comparative Example 2: This comparative example differs from Example 1 in that in step two, 1.746 g of cobalt nitrate, 0.226 g of stannous chloride dihydrate, 0.240 g of urea, and 0.333 g of ammonium fluoride were weighed and added to 60 mL of methanol. The other steps and parameters were the same as in Example 1.

[0050] Comparative Example 3: This comparative example differs from Example 1 in that in step two, 0.873 g of cobalt nitrate, 0.226 g of stannous chloride dihydrate, and 0.36 g of urea were weighed and added to 60 mL of methanol, and ammonium fluoride was not added. Other steps and parameters were the same as in Example 1.

[0051] Comparative Example 4: This comparative example differs from Example 1 in that in step two, 0.873 g of cobalt nitrate, 0.226 g of stannous chloride dihydrate, and 0.222 g of ammonium fluoride were weighed and added to 60 mL of methanol. No alkali source was added. Other steps and parameters were the same as in Example 1.

[0052] Comparative Example 5: This comparative example differs from Example 1 in that in step two, 0.226 g of stannous chloride dihydrate, 0.36 g of urea, and 0.222 g of ammonium fluoride were weighed and added to 60 mL of methanol (without a cobalt source). Other steps and parameters were the same as in Example 1.

[0053] Comparative Example 6: This comparative example differs from Example 1 in that in step two, 0.873 g of cobalt nitrate, 0.36 g of urea, and 0.222 g of ammonium fluoride were weighed and added to 60 mL of methanol without tin. Other steps and parameters were the same as in Example 1.

[0054] Comparative Example 7: This comparative example differs from Example 1 in that in step two, 0.872 g of nickel nitrate, 0.226 g of stannous chloride dihydrate, 0.36 g of urea, and 0.222 g of ammonium fluoride were weighed and added to 60 mL of methanol, and nickel nitrate was used instead of cobalt nitrate. Other steps and parameters were the same as in Example 1.

[0055] Comparative Example 8: This comparative example differs from Example 1 in that in step two, 0.873 g of cobalt nitrate, 0.136 g of zinc chloride, 0.36 g of urea, and 0.222 g of ammonium fluoride were weighed and added to 60 mL of methanol, and zinc chloride was used instead of stannous chloride dihydrate. Other steps and parameters were the same as in Example 1.

[0056] Comparative Example 9: This comparative example differs from Example 1 in that the selenization treatment in step four is carried out under the protection of argon gas, heated to 700°C at a rate of 2°C / min and held for 3 hours. Other steps and parameters are the same as in Example 1.

[0057] Comparative Example 10: This comparative example differs from Example 1 in that the solvothermal reaction temperature in step three is 90°C and the time is 24 hours. The other steps and parameters are the same as in Example 1.

[0058] Comparative Example 11: This comparative example differs from Example 1 in that carbon cloth is not added as a self-supporting structure, while the other steps and parameters are the same as in Example 1.

[0059] SEM images of the samples prepared in Comparative Examples 1–8 are as follows: Figure 7 As shown, Figure 7 As shown in Figure a, the CoSe2-SnSe2 material exhibits irregular nanowire shapes and a disordered arrangement, with an average nanowire diameter of approximately 19 nm and a length of approximately 1.8 μm. Performance test results are as follows: at a current density of 0.1 Ag... -1 Below, the specific capacity can be 652.5 mAh g -1 After 100 continuous charge-discharge cycles, the specific capacity remained at 518.1 mAh g. -1 Around 79.4% capacity retention was achieved at a current density of 5.0 Ag. -1 Below, the specific capacitance is 498.7 mAh g -1 Compared to Example 1, the rate performance and cycle stability of the electrode material in Comparative Example 1 decreased significantly, indicating that carbon cloth pretreatment has a significant impact on the morphology and sodium storage performance of the electrode material. This is because carbon cloth pretreatment can remove impurities from the surface of the carbon fiber cloth and functionalize the carbon fiber surface, thereby enabling the directional growth of bimetallic cobalt-tin-selenide one-dimensional nanowires, which is beneficial for forming a CoSe2-SnSe2 heterojunction nanowire array with controllable aspect ratio.

[0060] like Figure 7 As shown in b, in Comparative Example 2, after changing the raw material formulation, although the cobalt tin selenide still exhibits a one-dimensional nanowire structure (with an average diameter of about 30 nm and a length of about 2 μm), it cannot grow in an orderly and uniform manner on the carbon cloth. Instead, it aggregates and its electrochemical performance is significantly reduced. Under the same test conditions, the capacity retention rate is only 81.7%.

[0061] Depend on Figure 7 The samples prepared in Comparative Examples 3 and 4, shown in c and d, when not used in combination with a specific ratio of alkali source and additives, resulted in nanowires with small aspect ratios, low connectivity, small specific surface areas, or even the inability to prepare nanowire structures. These factors are detrimental to the improvement of their electrochemical performance, as can be demonstrated by the performance test results in Table 1.

[0062] Comparative Examples 5 and 6 investigated the effect of a single metal composition on the structure and properties of CoSe2-SnSe2 heterojunction nanowire arrays. Figure 7As shown in figure e, in the absence of a cobalt source, tin selenide grows uniformly in situ on carbon cloth in a layered structure, as... Figure 7 As shown in f, in the absence of a tin source, cobalt selenide is randomly distributed on the carbon cloth in a nanowire structure. The sodium storage performance of the above-mentioned tin selenide and cobalt selenide is shown in Table 1. It can be seen that the rate performance and cycle stability of the above-mentioned single metal selenide are significantly lower than those of the CoSe2 / SnSe2@CC nanowire array in Example 1. This is because the single metal selenide material prepared in the above comparative example cannot form a heterojunction structure and a one-dimensional nanowire array through the synergistic effect of metal ions in the reaction process. This is detrimental to the transfer of electron charge and the maintenance of the material morphology and structure, thus significantly reducing its performance.

[0063] Comparative Examples 7 and 8 investigated the preparation of corresponding bimetallic substances by replacing Co and Sn with different metals Ni and Zn, respectively. Their SEM images are shown below. Figure 7 g and Figure 7 As shown in h, although the obtained nickel-tin selenide and zinc-cobalt selenide have heterostructures, they do not have one-dimensional nanowire morphology. Since the composition control in the solvothermal-selenization reaction system of this invention is designed based on factors such as the strength of the selenide formation by cobalt and tin ions, lattice spacing, and barrier difference, when the type of metal ions changes, the reaction system cannot prepare bimetallic selenide materials that simultaneously have heterostructure, one-dimensional nanowires, and in-situ self-supporting arrays. Due to the inability to effectively combine the above advantages, their performance test results are not ideal, as shown in Table 1.

[0064] Comparative Examples 9 and 10 illustrate that selenization reaction and solvothermal conditions are also important influencing factors in the preparation process. Only by adjusting parameters such as temperature and time to achieve appropriate values ​​can ideal materials be obtained.

[0065] In Comparative Example 11, the untreated carbon cloth served as the support substrate for the self-supporting nanowire array. Although nanowire-shaped CoSe2-SnSe2 could be obtained, the lack of support and bonding led to significant morphological changes during charge and discharge. In particular, the severe collapse and pulverization during cycle testing caused a sharp decline in cycle performance (Table 1).

[0066] Table 1. Structural characteristics and sodium storage performance of the samples prepared in the examples and comparative examples.

[0067]

[0068]

[0069] In summary, the sodium storage performance of the electrode materials prepared in Comparative Examples 1-11 was lower than that of the electrode material in Example 1, further illustrating the importance of one-dimensional nanowire structures and bimetallic heterostructures with controllable aspect ratios for improving the electrochemical performance of electrode materials. Using cobalt nitrate and stannous chloride dihydrate as cobalt and tin sources, urea as the alkali source, and ammonium fluoride as an additive, a self-supporting bimetallic CoSe2-SnSe2 heterostructure nanowire array was synthesized in situ on carbon cloth. The addition and ratio of urea and ammonium fluoride were key factors in obtaining the one-dimensional nanowire structure. This was achieved by controlling the F-ion content in the alkaline system. - The concentration of the metal ions induces their unidirectional growth, and combined with appropriate solvothermal reaction conditions, a bimetallic heterojunction structure is formed. Controllable selenization treatment then endows the electrode material with advantages in interfacial charge transport, enhancing electrochemical reaction kinetics and facilitating rapid sodium ion diffusion, resulting in excellent electrochemical rate performance. The strong interaction between cobalt and tin enhances the local electronic states of tin atoms, thereby expanding the metal lattice spacing and lowering the diffusion barrier, strengthening the electrolyte's slow-release effect and further improving the electrochemical stability of the electrode material. Furthermore, the in-situ growth of the electrode material on pretreated carbon cloth ensures a tight and secure bond between the CoSe2-SnSe2 heterojunction nanowire array and the current collector, effectively preventing further stacking and collapse of the one-dimensional nanowires during the electrochemical reaction, further improving its cycle stability and rate performance. Therefore, when the self-supporting bimetallic CoSe2-SnSe2 heterojunction nanowire array is used as the negative electrode of a sodium-ion battery, it exhibits excellent sodium storage characteristics at a current density of 0.1 Ag. -1 After 100 cycles at the current density, the capacity remained at 885.4 mAh g. -1 Moreover, the material is simple to prepare, the raw materials are readily available, and the cost is low.

Claims

1. A sodium-ion battery anode material, characterized in that, The anode material is prepared by in-situ growth of self-supported cobalt-tin-selenide nanowires on carbon cloth, forming a one-dimensional nanowire array. The cobalt-tin-selenide nanowires are composed of CoSe2-SnSe2 heterojunctions, and the one-dimensional nanowires are uniformly grown in situ on the carbon cloth. The preparation method of the sodium-ion battery anode material is carried out according to the following steps:

1. Pre-treat the carbon cloth; 2. Weigh out the cobalt source, tin source, alkali source, and additive according to the molar ratio of cobalt source, tin source, alkali source, and additive as (0.3~5):1:(1.7~20):(1.7~20), add them to the solvent, and sonicate them while stirring to fully dissolve them to obtain a mixture.

3. Transfer the mixture obtained in step 2 to the reactor, then vertically place the pretreated carbon cloth into the reactor, heat it to carry out a solvothermal reaction at a temperature of 100-150℃ for 5-24 hours, and cool it to room temperature to obtain the precursor.

4. Place the precursor obtained in step 3 downstream of the quartz tube of the tubular furnace, place a selenium source upstream of the quartz tube, and heat it to 300-600℃ at a rate of 1-10℃ / min under the protection of a protective gas for 1-6 hours for selenization treatment. During the selenization treatment, the flow rate of the protective gas is maintained at 60-1000mL / min. After natural cooling to room temperature, sodium-ion battery anode material is obtained.

2. The sodium-ion battery negative electrode material according to claim 1, characterized in that, The cobalt-tin-selenide nanowires have a diameter of 50–150 nm and an aspect ratio of 5–40.

3. A sodium-ion battery negative electrode material according to claim 1 or 2, characterized in that, The pretreatment described in step one is as follows: first, the carbon cloth is ultrasonically cleaned in acetone, concentrated nitric acid with a mass percentage concentration of 63%, concentrated sulfuric acid with a mass percentage concentration of 98%, ethanol, and deionized water for 5 to 30 minutes each, and then dried in a forced-air drying oven at a temperature of 40 to 80°C for 4 to 8 hours to obtain clean carbon cloth.

4. A sodium-ion battery negative electrode material according to claim 1 or 2, characterized in that, The cobalt source mentioned in step two is one or more of cobalt nitrate, cobalt chloride, cobalt acetate tetrahydrate, and cobalt hydroxide.

5. A sodium-ion battery negative electrode material according to claim 1 or 2, characterized in that, The tin source mentioned in step two is one or more of stannous chloride, tin oxide, and tin sulfide.

6. A sodium-ion battery negative electrode material according to claim 1 or 2, characterized in that, The alkaline source mentioned in step two is one or more of urea, ammonia water with a mass percentage concentration of 25%, sodium hydroxide, and potassium hydroxide.

7. A sodium-ion battery negative electrode material according to claim 1 or 2, characterized in that, The additives mentioned in step two are one or more of sodium citrate, ammonium fluoride, and hexamethylenetetramine.

8. A sodium-ion battery negative electrode material according to claim 1 or 2, characterized in that, The solvent mentioned in step two is one or more of water, methanol, ethanol, ethylene glycol, and dimethylformamide.

9. The application of the sodium-ion battery negative electrode material according to claim 1 or 2 as a sodium-ion battery negative electrode sheet, characterized in that, This application involves using negative electrode materials to create negative electrode sheets for use as the negative electrode in sodium-ion batteries.

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