Carbon-coated tin nanoparticles, preparation method thereof, and lithium-ion battery material thereof

Abstract

The present invention discloses a carbon-coated tin nanoparticle, a preparation method thereof, and a lithium-ion battery material thereof, relating to the field of battery materials. The preparation method comprises: dissolving Bacillus subtilis spores in deionized water, adding glucose for activation and culturing to obtain a supernatant; adding SnCl4, incubating to obtain a suspension; adding a complexing agent, ultrasonically treating, centrifuging to remove the complex, and obtaining a centrifuge; collecting a precipitate by centrifugation; dissolving the precipitate in deionized water, ultrasonically oscillating to obtain a solution; dissolving carbon nanotubes or graphene oxide in a solvent to obtain a carbon nanotube solution or a graphene oxide solution; mixing the solution with the carbon nanotube solution to obtain a mixed solution; freeze-drying; and annealing the powder at high temperature under a protective gas atmosphere. The beneficial effect of the present invention is that the voids inside the bacterial carbon shell alleviate the volume expansion of the tin particles during the lithiation and delithiation processes, and the carbon nanotubes uniformly integrated in the bacterial carbon shell serve as efficient electron conduction channels to disperse anisotropic stress.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery materials, and in particular to carbon-coated tin nanoparticles, a preparation method thereof, and lithium ion battery materials thereof. Background Art

[0002] As the main energy source for portable electronic devices and electric vehicles, lithium-ion batteries have developed rapidly. However, traditional graphite anodes have difficulty in solving the problems of low energy density and short cycle life in electronic devices and electric vehicles, which has led to problems with battery capacity. In order to meet the growing demand for energy and usage, the development of high-energy-density lithium-ion batteries has become an important pursuit of researchers around the world. Traditional graphite anode materials have low energy density, theoretical capacity (372 mA hg - ¹) and slow lithium ion diffusion rate. Therefore, it is particularly important to explore and develop new alternative anode materials to improve energy density.

[0003] Currently, there are many high-capacity anode candidate materials, including materials based on silicon, germanium, tin, sulfides, and various alloys and metal compounds. Although silicon and germanium-based materials have extremely high theoretical capacities, they suffer from complex synthesis processes and low electrical conductivity. In contrast, tin anode materials have high electrical conductivity and high theoretical capacity (994 mA h g - ¹), has attracted widespread attention from researchers. However, due to the 22 During the formation of Sn5, tin anode materials undergo a volume expansion of up to 260% during charge-discharge cycling. This volume expansion causes irreversible structural damage during lithium-ion insertion and extraction, allowing the electrolyte to continuously penetrate the damaged structure, thereby reducing its overall performance over time. Consequently, the SEI (solid electrolyte interface) film that forms on the material's surface becomes thicker, hindering lithium-ion transport (thus reducing ionic conductivity), further leading to a rapid decline in battery capacity. Therefore, there is an urgent need to address the challenges in the application of tin-based materials.

[0004] To address this issue, researchers have focused on optimizing the morphology, electrical conductivity, and surface chemistry of tin anode materials to improve the performance of lithium-ion batteries. Jaegeon Ryu et al. used a template method to create a flexible 3D graphene-supported tin-based composite material with a double-layer coating (TiO2 and SnO2) to enhance electronic conductivity, reduce stress, and improve the stability and performance of lithium-ion battery anodes. Belgigayeva et al. used a one-pot electrospinning technique combined with heat treatment to prepare free-standing tin phosphide / phosphate carbon composite nanofiber mats as an alternative anode material for low-temperature lithium-ion batteries, and studied the material properties and activation mechanism. Xiaoxiao Hou et al. used a novel synthesis method to prepare a low-melting-point dimer bimetallic Sn-Bi@C composite material with excellent sodium storage performance, high specific capacity, outstanding cycle stability, and good rate performance. Li Rui et al. prepared nitrogen-doped carbon-coated heterostructured Sn / SnO2 microcubic powder (Sn / SnO2@NC) by hydrothermal method, polymerization, and carbonization process. The material exhibits high initial discharge capacity, excellent rate performance and good cycling stability, which can accelerate lithium ion transfer and accommodate volume changes. Xunfu Zhou et al. synthesized a SnO2@C@GS composite material through a simple hydrothermal method and subsequent sintering. This novel 3D nanostructure consists of SnO2@C core-shell nanospheres and nanochains anchored on wrinkled graphene sheets, showing high capacity, excellent cycle stability and rate performance, making it a promising high-rate and stable anode material in lithium batteries. Compared with the above methods, bio-template technology is an excellent and innovative strategy that can easily endow materials with structural specificity, complexity and complex functions derived from biomaterials. Summary of the Invention

[0005] The present invention aims to address at least one of the technical problems existing in the prior art. Tin-based materials are considered promising anode materials for lithium-ion batteries due to their high theoretical capacity, abundant resources, and suitable low discharge potential. However, a major problem they face in practical applications is the rapid capacity decay during cycling, primarily due to pulverization caused by volume changes. To extend the service life of tin-based anodes, the significant volumetric strain associated with lithium ion insertion and extraction must be mitigated.

[0006] To this end, the present invention provides carbon-coated tin nanoparticles, a preparation method, and lithium-ion battery materials. These materials utilize the unique biotemplate properties of Bacillus subtilis, using its bacterial shell as a biotemplate, biosorbent, and renewable carbon source. This method successfully prepared submicron-sized Sn@C@CNT and Sn@C / GO anode materials. Nanosized tin particles are encapsulated within the bacterial carbon shell (0.4 μm wide and 0.9 μm long), and carbon nanotubes (CNTs) or graphene oxide (GO) are composited on the exterior of the shell. In this design, the voids within the shell mitigate the volume expansion of the tin particles during lithiation and delithiation. The CNTs or GO uniformly integrated within the shell serve as efficient electron conduction pathways while dissipating anisotropic stress. This arrangement buffers the mechanical stress generated by volume changes, thereby enhancing structural integrity. Furthermore, the CNTs or GO serve as active sites for Li⁺, contributing to the increased specific capacity of the anode material. Comparative analysis of the electrochemical performance of Sn@C, Sn@C@CNT composites, and Sn@C / GO composites showed that the innovative Sn@C@CNT composites and Sn@C / GO composites exhibited excellent lithium storage capacity, high specific capacity, stable cycle performance, and excellent rate performance. Specifically, the Sn@C@CNT composites exhibited excellent lithium storage capacity at 100 mA g - ¹After 150 cycles at a current density of 721.68 mA hg, a high initial coulombic efficiency of 70.1% was achieved and a high current density of 721.68 mA hg was maintained. - These findings highlight the great potential of Sn@C@CNT composites as high-energy-density and stable anode materials. This invention proposes an innovative method to construct complex structures using a simple bio-templated approach, thereby advancing the application of tin-based materials in energy-related technologies.

[0007] The technical solutions of the present invention are as follows:

[0008] A first aspect of the present invention provides a method for preparing carbon-coated tin nanoparticles, comprising the following steps:

[0009] S1. Dissolve Bacillus subtilis spores in deionized water, add glucose to activate the culture, and centrifuge to obtain the supernatant;

[0010] S2. Add SnCl4 to the supernatant of step S1 and incubate to obtain a suspension;

[0011] S3, adding a complexing agent to the suspension of step S2, ultrasonically treating, and centrifuging to remove the complex to obtain a centrifuge;

[0012] S4, centrifuging the centrifuge liquid of step S3, collecting the precipitate; dissolving the precipitate in deionized water, ultrasonically oscillating, and obtaining the precipitate containing adsorbed Sn. 4+ a solution of Bacillus subtilis;

[0013] S5, dissolving the carbon nanotubes or graphene oxide in a solvent, and applying ultrasonic vibration to obtain a carbon nanotube solution or a graphene oxide solution;

[0014] S6, mixing the solution of step S4 with the carbon nanotube solution of step S5, and performing ultrasonic oscillation to obtain a mixed solution;

[0015] S7, freeze-drying the mixed solution of step S6 to obtain a powder;

[0016] S8. The powder obtained in step S7 is placed in a protective gas atmosphere and subjected to high-temperature annealing to obtain carbon-coated tin nanoparticles.

[0017] Optionally, in step S1, the mass ratio of Bacillus subtilis spores to glucose is 10-12:2-3; the activation culture time is 14-18 hours, the centrifugal speed is 1500-2000 rpm, and the centrifugation time is 1-3 minutes.

[0018] Optionally, in step S2, the addition ratio of Bacillus subtilis spores to SnCl4 is 10-12 g: 2 mL, and the incubation time is 16 to 24 hours.

[0019] Optionally, in step S3, the molar ratio of the complexing agent to SnCl4 is 1-4:1-2, the ultrasonic treatment time is 20-40 minutes, the centrifugal speed is 1600-1700 rpm, and the centrifugal time is 1-3 minutes.

[0020] Optionally, in step S3, the complexing agent is EDTA.

[0021] Optionally, in step S4, the centrifugal speed is 4000-5000 rpm, the centrifugal time is 5-7 minutes, the ultrasonic oscillation frequency is 35-45 KHz, and the ultrasonic oscillation time is 5-7 hours.

[0022] Optionally, in step S5, the amount of carbon nanotubes or graphite oxide added is 1-4% of the mass of the precipitate, the frequency of ultrasonic oscillation is 35-45 kHz, and the time of ultrasonic oscillation is 5-7 hours.

[0023] Optionally, the solvent in step S5 is ethanol.

[0024] In step S6, the frequency of ultrasonic oscillation is 35-45 KHz, and the time of ultrasonic oscillation is 1-3 hours.

[0025] Optionally, in step S7, the freezing time is 3-5 hours and the drying time is 20-28 hours.

[0026] Optionally, in step S7, the high temperature annealing temperature is 780-820° C., the heating rate is 8-10° C. / min, and the time is 15-30 minutes.

[0027] The second aspect of the present invention provides carbon-coated tin nanoparticles prepared by the method described above.

[0028] The third aspect of the present invention provides a lithium-ion battery material comprising the carbon-coated tin nanoparticles.

[0029] The present invention has at least one of the following beneficial effects:

[0030] The present invention proposes a simple and cost-effective bio-cultivation method to engineer a material in which a tin-based component is encapsulated within bacterial cells and coated with carbon nanofibers (Sn@C / CNT) or graphene oxide (Sn@C / GO) on the surface. The carbon shell on the bacterial surface effectively maintains the structural and interfacial stability of the tin nanoparticles, inhibits their aggregation, and buffers volume expansion. In addition, the carbon nanofiber network on the surface has high conductivity, large surface area, and excellent mechanical flexibility, which can firmly anchor the core-shell structure of Sn@C. This design significantly enhances the conductivity and structural integrity of the overall electrode. When used as an anode material in lithium-ion batteries, Sn@C / CNT exhibits a high initial coulombic efficiency of 71% and a high charge and discharge rate at 100mA g - ¹After 150 cycles, it has a current density of 721.68 mA h g - ¹, and exhibits excellent reversible capacity, good rate capability, and outstanding cycling stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Synthesis flow chart of Sn@C and Sn@C / CNT composites.

[0032] Figure 2 Figure 3 shows the morphology and structure of Sn@C / CNT. (a, b, c) Scanning electron microscope images of Sn@C / CNT; d, e) TEM images showing the overall and local structures, respectively; f) TEM image highlighting the surface carbon shell; g, h) Local TEM images of tin (Sn) within the carbon shell; i, j, k) Elemental maps of tin and carbon.)

[0033] Figure 3Characterization of Sn@C / CNT. A) X-ray diffraction (XRD) pattern; b) Raman spectroscopy; c, d) thermogravimetric analysis (TGA) and differential thermal analysis (DTG); e, f) X-ray photoelectron spectroscopy (XPS) of C1s and Sn3d.

[0034] Figure 4 Figure 2 shows the electrochemical performance of Sn@C and Sn@C / CNT. a) Cyclic voltammograms of Sn@C / CNT in the voltage range of 0.01 to 3.0 V at a scan rate of 2 mV / s for the first five cycles. b, c) Cyclic voltammograms of Sn@C / CNT in the voltage range of 0.01 to 3.0 V at a scan rate of 2 mV / s for the first five cycles. -1 Specific capacities of Sn@C and Sn@C / CNT batteries from the 1st to the 150th cycle at current densities of 100 mA g -1 Cycling performance and Coulombic efficiency at different current densities (100, 200, 400, 600, 800, and 1000 mA g) of Sn@C and Sn@C / CNT. -1 g) Electrochemical impedance spectroscopy (EIS) of Sn@C / CNT anode material after one cycle and 150 cycles.

[0035] Figure 5 The morphology and structure of Sn@C materials are shown. (a) SEM image of the material synthesized with EDTA (Sn-EDTA molar ratio of 1:1); (b) SEM image of the material synthesized with EDTA (Sn-EDTA molar ratio of 2:1); (c) SEM image of the material synthesized with EDTA (Sn-EDTA molar ratio of 1:2); (d) SEM image of the material synthesized with EDTA (Sn-EDTA molar ratio of 1:4); (e) XRD patterns of materials synthesized with different Sn:EDTA molar ratios (1:1, 2:1, 1:2, 1:4).

[0036] Figure 6 This is the scanning electron microscopy image of Sn@C material without EDTA.

[0037] Figure 7 The morphology and structure of Sn@C and Sn@C / CNT, including: a) high-resolution TEM (transmission electron microscopy) and b) lattice fringes shown in SAEM (selected area electron microscopy) images. c) High-resolution SEM (scanning electron microscopy) image of bacterial fracture in Sn@C.

[0038] Figure 8This is the EDX spectrum of Sn@C / CNT.

[0039] Figure 9 Scanning electron microscope images of Sn@C / CNT with different proportions of carbon nanotubes, among which (a) and (b) are SEM (scanning electron microscope) images of Sn@C / CNT materials containing different proportions of carbon nanotubes (1%, 2%, 3%, 4%).

[0040] Figure 10 XRD patterns of Sn@C / CNT at different CNT contents (1%, 2%, 3%, 4%).

[0041] Figure 11 SEM images of Sn@C / GO with different CNT contents (1%, 2%, 3%, 4%); a) Scanning electron microscopy (SEM) images of Sn@C / GO materials containing different proportions of graphene oxide (1%, 2%, 3%, 4%).

[0042] Figure 12 The effects of adding different ratios of carbon nanotubes (CNTs) and graphene oxide (GO) on the cycling stability of batteries. a) Different CNT contents (initial, 1%, 2%, 3%, 4%) of materials at 100 mA g -1 Electrochemical performance under current density; b) Electrochemical performance of materials with different GO contents (1%, 2%, 3%, 4%) at 100 mA g -1 Electrochemical performance at different current densities.

[0043] Figure 13 At 500 mA g -1 Nyquist plot equivalent circuit model after 200 cycles under the same conditions.

[0044] Figure 14 Scanning electron microscope images of the electrodes. (a) Sn@C / CNT-1% before cycling; (b) Sn@C / CNT-1% after cycling, showing structural changes; (c) Sn@C / GO-2% before cycling; (d) Sn@C / GO-2% after cycling, highlighting morphological differences. DETAILED DESCRIPTION

[0045] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0046] The present invention is further described in detail below with reference to specific examples, but the present invention is not limited to the following specific examples.

[0047] Sources of the raw materials in the following examples: Bacillus subtilis (provided by Hebei Longyang Biotechnology Co., Ltd., China), glucose (C6H 12 O6·H2O, Aladdin Biochemical Technology Co., Ltd., China), deionized water (homemade), EDTA (ethylenediaminetetraacetic acid, Xilong Science Co., Ltd., China), SnCl4 (tin tetrachloride, MacLean Biochemical Technology Co., Ltd., China), carbon nanotubes (CNTs, Jiangsu Xianfeng Nanomaterials Co., Ltd., China).

[0048] Comparative Example 1

[0049] This comparative example provides a method for synthesizing Sn@C, comprising the following steps:

[0050] Ten grams of Bacillus subtilis spores were dissolved in 250 milliliters of deionized water, 2 grams of glucose was added, and the mixture was placed in a Petri dish. After activation and incubation for 16 hours, a mixed solution of Bacillus subtilis and glucose was obtained. To isolate pure and active Bacillus subtilis, the mixture was centrifuged at 1500 rpm for 2 minutes, the supernatant was decanted into a clean Petri dish, and the precipitate was discarded. To the Petri dish containing the supernatant, 2 milliliters of SnCl₄ solution was added, the mixture was stirred thoroughly, and incubated for 24 hours to obtain a suspension containing SnCl₄ and Bacillus subtilis. This suspension was then added with different ratios of EDTA (the molar ratio of EDTA to SnCl₄ was 1:2, 2:1, 4:1, and 1:1, respectively), sonicated for 30 minutes, and then centrifuged at 1600 rpm for 2 minutes to remove surface chelates. This resulted in a solution containing Bacillus subtilis spores adsorbed with Sn ions. Finally, the solution was centrifuged at 4500 rpm for 7 minutes to collect the precipitate, which was then resuspended in ethanol and centrifuged again at 4500 rpm for 5 minutes to collect the final precipitate. The precipitate was freeze-dried for 24 hours and then annealed at 800°C for 30 minutes in a tube furnace under an argon atmosphere to obtain [Sn@C].

[0051] The overall synthesis process of Sn@C is as follows Figure 1 As shown in Figure 2. The process involves two main strategies. First, Bacillus subtilis (BS) adsorbs metal salts (SnCl4). In this step, the bacteria are cultured in deionized water containing glucose for 16 hours to obtain a bacterial precursor solution. In our experiments, when excess SnCl4 (2 mL added to 200 mL deionized water) was introduced into the BS solution after 16 hours of culture at room temperature, the bacteria died or entered a dormant state. The bacteria adsorbed Sn through their cell walls. 4+ions and retained internally. Next, Sn was adsorbed by centrifugation at different speeds. 4+ ions of bacteria and add them to EDTA solution to remove Sn on the surface 4+ Finally, the annealing was carried out in an argon-filled tube furnace at a heating rate of 7°C per minute to 800°C and maintained for 30 minutes. During the annealing process, the bacterial cell wall was converted into carbon, and the high-temperature annealing reduction process reduced the adsorbed Sn 4+ The ions are converted to elemental Sn.

[0052] Figure 6 The SEM images in Figure 2 show that without EDTA, there is a thick adhesion layer and a large number of aggregated Sn balls on the surface of the Sn@C material. Figure 5 As shown in (bd), the surface of the bacterial template becomes cleaner and cleaner, and the size of the Sn spheres decreases. Figure 6 It can be observed that the diameter of the solder balls is about 1.2 microns. Figure 5 (ad) show the SEM images of Sn:EDTA ratios of 1:1, 2:1, 1:2, and 1:4. Figure 5 b, we can see that the diameter of the solder ball has been reduced to 0.6 microns. Figure 5 c shows that the number of solder balls is reduced. However, Figure 5 As shown in d, only a small amount of Sn particles remain on the surface, while Figure 5 These tin balls or tin particles in a almost completely disappeared, indicating that the surface Sn 4+ It can be removed by complexation using EDTA. XRD analysis ( Figure 5 e) shows that with the increase of EDTA content, the intensity of XRD peak gradually decreases, but it has little effect on the appearance of Sn peak. It can be determined that the 1:1 ratio of Sn to EDTA is the best ratio in removing surface Sn. 4+ After the bacteria have been treated, a large amount of Sn is still retained inside the bacteria. This phenomenon is attributed to the bacteria's 4+ The adsorption effect hinders the complexing agent from reacting with the internal Sn 4+ reaction.

[0053] Example 1

[0054] This embodiment provides a method for synthesizing carbon-coated tin nanoparticles (Sn@C / CNT), comprising the following steps:

[0055] Ten grams of Bacillus subtilis spores were dissolved in 250 milliliters of deionized water, 2 grams of glucose was added, and the spores were placed in a Petri dish. After activation and incubation for 16 hours, a mixed solution of Bacillus subtilis and glucose was obtained. To isolate pure and active Bacillus subtilis, the mixture was centrifuged at 1500 rpm for 2 minutes, the supernatant was decanted into a clean Petri dish, and the precipitate was discarded. To the Petri dish containing the supernatant, 2 milliliters of SnCl₄ solution was added, the mixture was stirred thoroughly, and incubated for 24 hours to obtain a suspension containing SnCl₄ and Bacillus subtilis. This suspension was then sonicated for 30 minutes at different ratios of EDTA (the molar ratio of EDTA to SnCl₄ was 1:2, 2:1, 4:1, and 1:1, respectively). The suspension was then centrifuged at 1600 rpm for 2 minutes to remove surface chelates. This resulted in a solution containing Bacillus subtilis spores adsorbed with Sn ions. Finally, the solution was centrifuged at 4500 rpm for 7 minutes, and the precipitate was collected.

[0056] The resulting lower precipitate was dissolved in a beaker containing 25 ml of deionized water. In another beaker, 25 ml of ethanol was added, along with 1%, 2%, 3%, and 4% (1%, 2%, 3%, and 4% of the mass of the lower precipitate) of carbon nanotubes (CNTs), respectively. The two beakers were placed in an ultrasonic oscillator set to 40 kHz and oscillated for 6 hours. The solutions in the two beakers were then combined into one beaker and oscillated under the same conditions for another 2 hours. The resulting solution was then placed in a freeze dryer, frozen for 4 hours, and dried for 24 hours. Finally, the resulting powder was transferred to a tube furnace and annealed under an argon atmosphere at 800°C for 30 minutes at a heating rate of 9°C per minute to obtain [Sn@C / CNT].

[0057] In order to enhance the conductivity of the material, Figure 1 The method shown in the figure adds a small amount of carbon nanotubes based on comparative example 1. 4+ Then, carbon nanotubes were introduced in a specific ratio. After thorough mixing, the mixture was placed in an argon-filled tube furnace and annealed at 800°C for 30 minutes at a heating rate of 9°C per minute.

[0058] Figure 2 (ac) Show the surface morphology of C-coated Sn nanostructures synthesized by the bio-template method, observed using SEM. Figure 2 In c, the SEM image shows a rod-shaped bacterial structure with a size of approximately 0.8 µm long and 0.4 µm wide, covered with carbon nanotubes ( Figure 2 b), which results in closer contact between bacteria. TEM image ( Figure 2 e) also clearly shows this rod-shaped morphology, Figure 2f shows that there is a clear boundary layer with a thickness of 6 nm on the surface, which is the result of carbonization of the bacterial shell during annealing.

[0059] In order to further confirm the Sn 4+ Whether it has been completely removed, it is necessary to verify Sn 4+ Has it been internally absorbed? The high-resolution TEM images highlight the clear crystal phase of Sn. According to these HR-TEM images ( Figure 7 a) The calculated d-spacing of the lattice fringe is 0.29 nm. Selected area electron diffraction (SAED) pattern ( Figure 7 b) shows diffraction rings consistent with the single crystal structure of Sn. TEM image ( Figure 2 g) reveals that the internal structure is composed of bulk Sn. Figure 2 h, the measured sizes of bulk Sn along three different axes are 36.08 nm, 68.25 nm and 102.61 nm, respectively, indicating that Sn is retained inside the bacteria in the form of nanoparticles and has not aggregated into Sn balls. Figure 7 c), this conclusion is further supported. In addition, the element mapping image ( Figure 2 i, j, k) show that Sn and C are evenly distributed inside the bacteria. These results indicate that Sn@C / CNT has an excellent morphological structure.

[0060] To further confirm the structural characteristics of the material, XRD analysis showed obvious diffraction peaks at 2θ of 30.644°, 32.018°, and 43.871°, corresponding to the (200), (101), and (221) crystal planes, respectively ( Figure 3 a). These diffraction peaks indicate that the Sn nanostructures are well-crystalline and exhibit a tetragonal structure. The lattice parameters calculated from the XRD data are a = 5.832 nm and c = 3.181 nm. Notably, no secondary peaks associated with impurities or other Sn phases are observed, demonstrating that the chelation method is highly effective in removing excess Sn from the surface, thereby preventing the introduction of other impurities.

[0061] In Raman spectroscopy ( Figure 3 b), 1335 cm - ¹ and 1581 cm - The two main peaks at ¹ correspond to the D band and the G band, respectively. The D band represents defects in amorphous carbon, while the G band is characteristic of graphitic carbon. The ID / IG ratio exceeds 0.99, reflecting the presence of a large number of microstructural defects in the carbon shell, indicating that there are many defects and vacancies in the carbon shell, and also a certain degree of graphitization. This coexistence of graphitization, defects, and vacancies not only accelerates the Li + transmission, also for Li +The storage provides numerous active sites.

[0062] TGA Figure 3 c) and DTG ( Figure 3 d) The component content of the material was quantitatively analyzed in air. Below 300°C, the weight loss curve showed a loss of approximately 7.41%, mainly due to water evaporation and a slight reaction of reduced phosphorus (P) and sulfur (S) inside the bacteria with oxygen. The mass loss between 400°C and 600°C was approximately 40.7%, attributed to the reaction of surface carbon (C) with air to produce CO2. At approximately 566°C, the TGA curve showed a significant decrease in slope and a local minimum in the DTG curve, indicating that Sn reacted with air to produce SnO2, resulting in an increase in mass. Despite this, the overall trend of the TGA curve was downward, and the final mass remained at 51.9%. Figure 3 It can be analyzed that trace amounts of other metal elements (such as Ca, Mg, and Al) are present within the pure bacteria. To better analyze the Sn content, the Sn@C / CNT material was dissolved and diluted 10,000 times, and the Sn content was measured to be 16.96%, as shown in Table 1.

[0063] Table 1

[0064]

[0065] X-ray photoelectron spectroscopy (XPS) was used to study the chemical composition and bonding state of the Sn@C / CNT electrode, confirming the presence of C and Sn. Figure 3 As shown in e and f, the high-resolution spectra of C 1s and Sn 3d were analyzed. Figure 3 e), the three fitted peaks at 284.8 eV, 285.7 eV, and 286.8 eV correspond to C=C, CO, and C=O bonds, respectively. Figure 3 f), the two peaks at 495.8 eV and 486.3 eV are attributed to Sn, respectively. 0 3d 5 / 2 and 3D 3 / 2 The peaks at 487.3 eV and 498.5 eV correspond to Sn 4+ 3d 5 / 2 and 3D 3 / 2 , while the peak at 496.8 eV is attributed to Sn-O, indicating the presence of oxidized Sn on the surface. Figure 8 This is the EDX spectrum of Sn@C / CNT. The elements present in the material were analyzed using energy-dispersive X-ray spectroscopy (EDX). The main nonmetallic elements identified were C, O, P, and S, while the metallic elements included Ca, Mg, Al, Sn, and Na. Figure 8It also showed that the presence of small amounts of oxygen in the bacteria led to the formation of trace amounts of SnO2.

[0066] Example 2

[0067] This embodiment provides a method for synthesizing carbon-coated tin nanoparticles (Sn@C / GO). The preparation method is the same as that of Example 1, except that the carbon nanotubes in Example 1 are replaced with graphene oxide. The other steps are the same as those of Example 1.

[0068] The graphene oxide is prepared according to the Hummers method.

[0069] Example 3

[0070] The Sn@C synthesized in Comparative Example 1, the Sn@C / CNT synthesized in Example 1, and the Sn@C / GO synthesized in Example 2 were used as lithium-ion battery materials and applied in lithium-ion batteries to test the electrochemical properties of Sn@C, Sn@C / CNT, and Sn@C / GO.

[0071] The electrochemical performance of Sn@C, Sn@C / CNT, and Sn@C / GO was evaluated using lithium metal coin cells as the counter electrode.

[0072] Electrochemical performance was tested using CR2032 button cells. The working electrode was prepared by mixing the active material, acetylene black, and polyvinylidene fluoride (PVDF) in a mass ratio of 80:10:10 in N-methyl-2-pyrrolidone (NMP) to form a uniform slurry. The slurry was coated onto a copper foil substrate and then dried overnight in a vacuum oven at 55°C. The cell was assembled in a glove box filled with high-purity argon. Pure lithium sheets were used as the counter and reference electrodes, Celgard 2400 membrane was used as the separator, and 1.0 M LiPF₆ dissolved in a 1:1:1 (volume) mixture of EC (ethylene carbonate), DMC (dimethyl carbonate), and EMC (ethyl methyl carbonate) was used as the electrolyte.

[0073] Figure 4a shows representative cyclic voltammograms (CVs) for the first five cycles over a voltage range of 0.01 to 3.0 V at a scan rate of 2 mV / s. Electrochemical kinetic analysis revealed that the first discharge cycle exhibited two subtle peaks at 0.83 V and 1.19 V, while the first charge cycle exhibited two similar, but less pronounced, peaks at 0.76 V and 1.41 V, respectively. These peaks became more pronounced with subsequent cycles. During the second charge-discharge cycle, two distinct peaks at 0.83 V and 1.41 V were observed, attributed to the reversible reaction between the surface carbon layer and lithium ions (Equation 1). The peaks at 1.19 V and 0.76 V are associated with the reversible alloying reaction between Sn and lithium ions (Equation 2). These peaks gradually stabilized with increasing cycle number, demonstrating the good stability and excellent electrochemical reversibility of the Sn@C / CNT structure.

[0074]

[0075] Figure 4b and Figure 4c show the Sn@C and Sn@C / CNT-1% at a current density of 100 mA g -1 The charge-discharge curves for the 1st, 10th, 50th, 100th, and 150th cycles under the same conditions are shown in Figure 4b. In Figure 4b, the voltage platform observed in the range of 0–1.3 V during the first discharge is related to the formation of the SEI film and the insertion of lithium ions into the negative electrode material, achieving 573.1 and 848.5 mA h g, respectively. -1 The initial charge-discharge capacity is 1156.1 mA h g. -1 , indicating that Sn@C / CNT-1% has a higher discharge capacity than Sn@C. This enhancement is mainly attributed to the addition of CNTs, which increases the active sites of the material, improves the conductivity, and accelerates the transfer rate of lithium ions. The charge-discharge capacity curve from the 10th to the 150th cycle shows stability, indicating that Sn encapsulated in the carbon material effectively improves the electrochemical stability of the battery. After 150 charge-discharge cycles, Sn@C maintained a charge capacity of 534.45 mA h g -1 The reversible capacity of Sn@C / CNT-1% was 721.6 mA h g -1The reversible capacity of Sn@C / CNT-1% was 62.4% (capacity retention rate). Compared with Sn@C, Sn@C / CNT-1% showed higher initial and reversible capacity. The presence of CNTs slowed down the volume expansion of Sn to a certain extent, thereby maintaining the structural stability of the material and improving the electrochemical reversibility of the battery.

[0076] The cycling performance of the electrode is in the voltage range of 0.01−3.0 V and 100 mA g -1 As shown in Figure 4d, in the first cycle, the charge and discharge specific capacities of Sn@C / CNT-1% were 803.44 and 1156.16 mA h g -1 , while the capacities of Sn@C are 573.16 and 848.58 mA h g -1 . The observed large capacity irreversibility may be attributed to the consumption of electrolyte solution during the formation of SEI film. Figure 4e shows that the first coulombic efficiency (ICE) of Sn@C / CNT-1% is about 70.1%, while the coulombic efficiency of Sn@C is about 67.5%. However, after the second cycle, the coulombic efficiency rapidly increased to 99%. This result is consistent with many studies showing that the first coulombic efficiency is affected by the large amount of lithium ions consumed during the formation of SEI film on the electrode surface. This indicates that a stable SEI film is formed on the surface of the negative electrode material, which contributes to stable cycling performance. Compared with Sn@C, Sn@C / CNT-1% not only exhibits higher initial capacity and first coulombic efficiency, but also shows significantly improved reversible capacity after 150 cycles, reflecting superior electrochemical stability. This enhancement is attributed to the addition of CNTs, which increases the active sites of the material, improves conductivity, accelerates lithium ion transport, and partially slows down the volume expansion of Sn.

[0077] Figure 4 f shows the performance of Sn@C / CNT-1% and Sn@C at different current densities. For Sn@C / CNT-1%, the performance of Sn@C / CNT-1% at different current densities (100, 200, 400, 600, 800 and 1000 mA g -1 ) are approximately 705.54, 543.66, 443.25, 392.24, 366.70, and 362.72 mA h g -1 When the current density returns to 100 mAg -1 When the charge and discharge capacity of the battery is restored to 606.53 mA h g -1For Sn@C, the reversible capacities at the same current density are approximately 436.89, 326.65, 250.52, 212.66, 199.10, and 192.23 mA h g -1 . Restore to 100mA g -1 When the charge-discharge specific capacity of Sn@C is restored to 322.53 mA h g -1 . Figure 4 g shows the Nyquist plot of Sn@C / CNT before and after 150 cycles, obtained by electrochemical impedance spectroscopy (EIS) with a frequency range of 100 kHz to 0.01 Hz and an amplitude of 10 mV. Fitted using the equivalent circuit model Figure 13 Electrochemical impedance spectroscopy (EIS) data for the cell show two main impedance components: Rs (ohmic resistance) and Rct (charge transfer resistance). Table 2 shows that after one cycle, the resistances of Rs and Rct are 171.3 Ω and 938.4 Ω, respectively. After 150 cycles, Rs and Rct decrease significantly to 19.49 Ω and 138.1 Ω. This indicates that the cell exhibits good ionic conductivity and forms a stable solid electrolyte interface (SEI) layer during cycling. The stability of the impedance components contributes to the excellent cycling performance of the Sn@C / CNT cell.

[0078] Table 2 Sn@C / CNT as lithium-ion battery anode at 500 mA g - Nyquist plot fitting results after 200 cycles

[0079]

[0080] This example also studies the effect of adding different proportions of carbon nanotubes (CNTs) on the battery cycle stability. Materials with different CNT proportions were prepared and their morphology and structure were observed and analyzed using XRD and SEM. Figure 9 As shown in (ad), SEM images of materials with different CNT ratios (1%, 2%, 3%, and 4%) can be observed. As the CNT ratio increases, carbon nanotubes gradually aggregate into larger block structures. Figure 10 The XRD peaks of different CNT ratios correspond to the standard Sn card, confirming that Sn is still the main component of the material. We also prepared button batteries and tested them at a current density of 100 mAg −1 The cycling performance of the electrode was tested under the conditions of 0.01-3 V. Figure 12As shown in a, the initial Coulombic efficiencies of different CNT ratios (1%, 2%, 3%, 4%, and 0%) are 70.1%, 34.6%, 41.2%, 79.9%, and 67.0%, respectively. After multiple cycles, the Coulombic efficiency stabilizes at approximately 99%. After 150 cycles, the reversible capacities of different CNT ratios (1%, 2%, 3%, 4%, and 0%) are 721.68, 420.37, 335.80, 380.23, and 463.34 mA h g, respectively. −1 The results showed that a 1% CNT addition ratio was optimal, as it not only increased the initial Coulombic efficiency but also improved the cycling stability of the anode material.

[0081] This example also studies the effect of graphene oxide (GO) on the material. By preparing materials with different GO ratios and observing their morphology and structure using SEM, we gain insights into the effect of GO addition. Figure 11 As shown in Figure 2, SEM images of materials with different GO ratios (1%, 2%, 3%, and 4%) can be seen. As the GO ratio increases, GO covers the surface of the material, forming a "sandwich" structure. We prepared a button cell and tested it at a current density of 100 mA g −1 The cycling performance of the electrode was tested under the conditions of 0.01-3 V. Figure 12 b shows that the initial Coulombic efficiencies of different GO ratios (1%, 2%, 3%, 4%) are 51.1%, 52.1%, 58.8% and 65.8%, respectively. After multiple cycles, the Coulombic efficiency stabilizes at about 99%. After 150-200 cycles, the reversible capacities of different GO ratios (1%, 2%, 3%, 4%) are 473.74, 611.23, 536.98 and 283.67 mA h g-1, respectively. The results show that the material with 2% GO added exhibits the best cycling performance. In summary, adding GO to Sn@C / GO materials can improve the Coulombic efficiency and reversible specific capacity. However, compared with Sn@C / GO, Sn@C / CNT materials perform better in charge and discharge specific capacity and cycle stability. As Figure 12 As shown in Figure 2, the specific capacities of the samples with 1% CNT and 2% GO after 150 cycles were 721.68 mA h g -1 and 611.23 mA hg -1 In addition, the cycling curve of 1% CNT is significantly more stable than that of 2% GO, confirming that adding 1% CNT is the optimal ratio to improve the performance of the material. As shown in Table 1, compared with other materials, this material has the characteristics of simple preparation method and excellent electrochemical performance.

[0082] In order to better understand the role of carbon nanotubes and graphene oxide in improving the electrochemical performance of Sn@C / CNT-1% and Sn@C / GO-2% composites, we used scanning electron microscopy to analyze the morphological changes of the electrodes before and after cycling, e.g. Figure 14 shown. Figure 14 a and Figure 14 b shows the SEM images of the Sn@C / CNT-1% electrode before and after cycling. Figure 14 In a, the carbon nanotubes are clearly visible and evenly distributed within the material, which is beneficial to internal connectivity and improves the electrical conductivity, thereby increasing the utilization of active materials and improving the electrochemical performance. Figure 14 As shown in (b), the boundaries between carbon nanotubes are no longer clear, the active material agglomerates, and there is a significant volume expansion. However, no obvious structural fragmentation is observed, and the integrity of the overall structure is maintained. Figure 14 c and Figure 14 d shows the SEM images of the Sn@C / GO-2% electrode before and after cycling. Figure 14 In c, we can see the graphene oxide structure covering the surface of the bacteria. After the cycle, Figure 14 d shows that the structure of graphene oxide is partially destroyed, forming a smaller layered structure that is evenly distributed on the surface of the material. This also explains the Figure 12 b) Capacity recovery. However, the capacity of the GO-based material is lower than that of the CNT-based material. This is likely due to the uneven initial distribution of GO around the tin particles, which results in reduced conductivity and less efficient utilization of the active material. Consequently, the electrochemical performance of the GO composite at the beginning of cycling is inferior to that of the CNT composite.

[0083] In summary, the present invention employed a simple bio-templated method to synthesize Sn@C / GO nanostructures with Sn@C / CNT nanostructures and a maximum reversible capacity of 721.68 mA hg⁻¹. Half-cell studies of the synthesized Sn@C / CNT- and Sn@C / GO structures demonstrated that superior materials can be obtained by incorporating CNTs or GO into Sn@C. The bacterial-derived carbon shell significantly mitigated the volume expansion of Sn, while the surface carbon nanotubes or graphene oxide enhanced conductivity and ion transport efficiency, thereby accelerating reaction kinetics. This present invention presents a novel and highly feasible approach to designing anode materials with high reversible capacity and excellent stability.

[0084] This work was supported by the Natural Science Foundation of Jiangxi Province (No. 20202BABL204049).

[0085] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing carbon-coated tin nanoparticles, characterized in that: The following steps are involved: S1. Dissolve Bacillus subtilis spores in deionized water, add glucose to activate the culture, and centrifuge to obtain the supernatant; S2. Add SnCl4 to the supernatant of step S1 and incubate to obtain a suspension; S3, adding a complexing agent to the suspension of step S2, ultrasonically treating, and centrifuging to remove the complex to obtain a centrifuge; S4, centrifuging the centrifuge liquid of step S3, collecting the precipitate; dissolving the precipitate in deionized water, ultrasonically oscillating, and obtaining the precipitate containing adsorbed Sn. 4+ a solution of Bacillus subtilis; S5, dissolving the carbon nanotubes or graphene oxide in a solvent, and applying ultrasonic vibration to obtain a carbon nanotube solution or a graphene oxide solution; S6, mixing the solution of step S4 with the carbon nanotube solution or graphene oxide solution of step S5, and subjecting to ultrasonic oscillation to obtain a mixed solution; S7, freeze-drying the mixed solution of step S6 to obtain a powder; S8. The powder obtained in step S7 is placed in a protective gas atmosphere and subjected to high-temperature annealing to obtain carbon-coated tin nanoparticles.

2. The preparation method according to claim 1, characterized in that In step S1, the mass ratio of Bacillus subtilis spores to glucose is 10-12:2-3; the activation culture time is 14-18 hours, the centrifugal speed is 1500-2000 rpm, and the centrifugation time is 1-3 minutes.

3. The preparation method according to claim 1, characterized in that In step S2, the addition ratio of Bacillus subtilis spores to SnCl4 is 10-12 g: 2 mL, and the incubation time is 16 to 24 hours.

4. The preparation method according to claim 1, characterized in that In step S3, the molar ratio of the complexing agent to SnCl4 is 1-4:1-2, the ultrasonic treatment time is 20-40 minutes, the centrifugal speed is 1600-1700 rpm, and the centrifugal time is 1-3 minutes.

5. The preparation method according to claim 1, characterized in that In step S4, the centrifugal speed is 4000-5000 rpm, the centrifugal time is 5-7 minutes, the ultrasonic oscillation frequency is 35-45 KHz, and the ultrasonic oscillation time is 5-7 hours.

6. The preparation method according to claim 1, characterized in that In step S5, the amount of carbon nanotubes or graphite oxide added is 1-4% of the mass of the precipitate, the frequency of ultrasonic oscillation is 35-45 kHz, and the time of ultrasonic oscillation is 5-7 hours; In step S6, the frequency of ultrasonic oscillation is 35-45 KHz, and the time of ultrasonic oscillation is 1-3 hours.

7. The preparation method according to claim 1, characterized in that In step S7, the freezing time is 3-5 hours, and the drying time is 20-28 hours.

8. The preparation method according to claim 1, characterized in that In step S7, the high temperature annealing temperature is 780-820°C, the heating rate is 8-10°C / min, and the time is 15-30 minutes.

9. Carbon-coated tin nanoparticles prepared by the method according to any one of claims 1 to 8.

10. A lithium-ion battery material, characterized in that: The carbon-coated tin nanoparticles according to claim 9 are included.

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