A capsule structure silicon-based in-situ nanocomposite wire bundle and a preparation method and application thereof

Abstract

This invention discloses a capsule-structured Si / SiO x @C In-situ Nanocomposite Wire Bundles, Their Preparation Method, and Applications. The core steps of this method are: first, a sodium silicate solution is mixed with a zinc ammonia complex solution and subjected to a hydrothermal reaction; then, the resulting product is dispersed in a glucose solution, and the hydrothermal reaction continues; finally, the product is subjected to magnesium thermothermal reduction to obtain the target material. The Si / SiO2 prepared by this invention... x @C composite materials exhibit a unique nanowire bundle morphology, with the nanowires forming a capsule structure. The components within these capsules achieve high dispersion and uniform distribution at the nanoscale due to in-situ reactions. The structural and compositional characteristics of this material have a synergistic effect in improving its electrochemical performance, significantly enhancing reversible capacity, initial coulombic efficiency, cycle stability, and rate performance, achieving a balance and optimization of multiple performance indicators. This material shows broad application prospects in the field of lithium-ion battery anode materials.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery electrode materials, specifically to a capsule-structured Si / SiO2. x @C in-situ nanocomposite wire bundles, their preparation methods, and applications. Background Technology

[0002] In pursuit of high energy density in lithium-ion batteries, silicon-based anode materials have become a research hotspot, primarily due to silicon's theoretical specific capacity of up to 3579 mAh / g. However, silicon-based anode materials face key bottlenecks in application, such as severe volume expansion, insufficient conductivity, and poor cycle stability, which seriously restrict their industrial application.

[0003] To address these issues, academia and industry have launched systematic explorations. Currently, mainstream optimization strategies mainly revolve around three dimensions: selection of active materials, innovation in composite processes, and microstructure design, aiming to achieve performance breakthroughs through multi-dimensional synergistic regulation.

[0004] First, regarding the selection of active materials, SiO x and Si / SiO x Composite systems have attracted much attention in recent years. Compared with pure silicon, SiO₂... x During the initial lithiation process, lithium oxide and lithium silicate are formed in situ. These inactive products act as an in-situ formed buffer framework, effectively absorbing volume expansion stress during cycling and maintaining the integrity of the electrode structure. Furthermore, the intrinsic properties of the Si-O covalent bond endow the material with superior structural stability compared to pure silicon. However, SiO... x Its inherent defects of low intrinsic conductivity and poor initial coulombic efficiency dictate that it must be compensated for through composite with highly conductive carbon materials and nano-scale design.

[0005] Secondly, at the composite process level, traditional composite methods often face the challenges of uneven component distribution and weak interfacial bonding. In-situ synthesis offers a superior solution to this problem. This method directly constructs composite materials through chemical reactions between precursors, achieving uniform dispersion of active materials, conductive media, and buffer phases at the nanoscale, and forming robust interfaces resembling chemical bonds. This refined microstructure facilitates the uniform release of stress during electrochemical reactions, suppressing crack initiation and propagation at their source.

[0006] Finally, at the structural design level, constructing hierarchical structures and nanocapsule encapsulation have proven to be highly promising methods for morphology control. On the one hand, assembling nanoscale units into micron-sized secondary particles not only retains the advantages of rapid reaction kinetics in nanomaterials but also solves the engineering problem of the random aggregation of nanoparticles through stable secondary morphology; at the same time, the reserved pores within the multi-level structure provide necessary buffer space for volume changes. On the other hand, encapsulating active particles in carbon nanocapsules achieves further functional differentiation: the internal nanoscale active material reduces intrinsic expansion stress, the flexible matrix absorbs volume changes, and the outer conductive carbon shell acts as an elastic constraint layer, playing a role similar to an "artificial SEI film," thereby stabilizing the electrode / electrolyte interface.

[0007] In summary, an ideal silicon-based anode material needs to balance high capacity of the active material, strong bonding at the composite interface, and stability of the microstructure. Inspired by the aforementioned multi-dimensional control concept, this invention focuses on the synergistic design of the material system and microstructure to construct a composite system with uniformly dispersed components and a stable structure, specifically providing a capsule-structured Si / SiO2. x @C In-situ Nanocomposite Wire Bundles, Their Preparation Methods and Applications, Through Integration of Si / SiO x The advantages of its components, the interface advantages of in-situ synthesis, and the structural advantages of the capsule wire bundle provide a practical and feasible technical path to solve the application bottleneck of silicon-based anodes and improve their electrochemical performance. Summary of the Invention

[0008] This invention proposes a capsule-structured Si / SiO x @C In-situ Nanocomposite Wire Bundles, Their Preparation Methods, and Applications. To achieve the above objectives, this invention provides the following technical solutions: A capsule structure Si / SiO x The preparation method of @C in-situ nanocomposite wire bundles includes the following steps: (1) Preparation of reaction mixture: Under stirring conditions, concentrated ammonia water is added to zinc acetate solution until the white precipitate just disappears completely to obtain zinc ammonia complex solution; then sodium silicate solution is added to the zinc ammonia complex solution to obtain reaction mixture; (2) Hydrothermal preparation of precursor: The reaction mixture obtained in step (1) is placed in a reaction vessel for the first hydrothermal reaction. After the reaction is completed, the precipitate is centrifuged and dried to obtain the precursor. (3) Hydrothermal carbon coating treatment of precursor: The precursor obtained in step (2) is dispersed in glucose solution and placed in a reaction vessel for a second hydrothermal reaction. After the reaction is completed, the product is centrifuged and dried to obtain carbon-coated precursor. (4) Magnesium reduction to prepare the target product: The carbon-coated precursor obtained in step (3) is mixed evenly with magnesium powder and sodium chloride. Under a protective atmosphere, the mixture is heated to carry out a magnesium reduction reaction. The resulting product is acid washed, separated, and dried to obtain a capsule-structured Si / SiO2. x @C in-situ nanocomposite wire bundle.

[0009] In the above preparation method, the molar ratio of zinc acetate and sodium silicate in step (1) is (2~6):5.

[0010] In the above preparation method, the temperature of the first hydrothermal reaction in step (2) is 180~220 ℃ and the time is 8~16 h.

[0011] In the above preparation method, the concentration of the glucose solution in step (3) is 15~50 mmol / L; the temperature of the second hydrothermal reaction is 160~200 ℃, and the time is 8~16 h.

[0012] In the above preparation method, the mass ratio of the carbon-coated precursor to magnesium powder and sodium chloride in step (4) is 1:(1~2):(5~15); the protective atmosphere is argon or argon-hydrogen mixture; the heating temperature of the magnesium thermal reduction reaction is 650~750 ℃, and the reaction time is 2~4 h.

[0013] This invention successfully constructed a Si / SiO with a unique hierarchical structure using the aforementioned in-situ preparation strategy. x @C nanocomposite material. This material exhibits a nanowire bundle assembly morphology, with its basic structural unit being a nanowire capsule unit. The nanowire capsule unit consists of a core and a shell: the core comprises highly dispersed Si nanoparticles and amorphous SiO₂. x The matrix is ​​a homogeneous composite; the outer shell is a continuous, uniform, and conformal carbon coating layer. Thanks to the material's bundle-like morphology, nanowire capsule unit structure, and internal homogeneity achieved through in-situ reaction, the synergistic effect of these three factors endows the material with excellent electrochemical performance, specifically manifested in: First, one-dimensional nanowires construct a highly efficient conductive network, accelerating the reaction. Their ordered assembly of nanowire bundles retains reaction sites while avoiding the excessive side reactions common in traditional nanoparticles. The divergent structure of the bundles not only buffers volume expansion and prevents electrode pulverization but also ensures thorough wetting by the electrolyte.

[0014] Secondly, the carbon layer is formed by the in-situ carbonization of glucose on the core surface and is conformal to the core, achieving continuous, uniform, and complete coating of the core. This carbon layer can serve as an artificial SEI film, isolating the electrolyte, inhibiting its decomposition, and ensuring that the SEI forms stably only on the carbon layer surface, reducing repeated damage. The carbon layer can rapidly transfer electrons, reduce interfacial impedance, buffer volume expansion, maintain structural integrity, prevent silicon from deactivating and becoming dead silicon, and ensure that the material maintains electrochemical activity during long-term cycling.

[0015] Third, the in-situ generated nano-silicon particles effectively alleviate the volume expansion of lithium intercalation, and their high dispersion characteristics ensure a uniform distribution of lithiation stress, preventing crack formation. The decomposition products of the silicon oxide matrix can absorb expansion stress, forming a dual buffer of "internal absorption and external restriction" with the external carbon shell, inhibiting structural collapse. This matrix can also anchor the nano-silicon, preventing aggregation during cycling, and its amorphous properties alleviate the stress mismatch at the silicon / carbon interface. The combined effect of these factors significantly improves the long-cycle stability of the electrode. Attached Figure Description

[0016] Figure 1 Sample 1 (Si / SiO) x @C), Comparison Sample 1 (Si / SiO) x (a) XRD pattern and (b) EDS pattern of control sample 2 (Si).

[0017] Figure 2 Sample 1 (Si / SiO) x @C) Scanning electron microscope images at different magnifications.

[0018] Figure 3 Sample 1 (Si / SiO) x The transmission electron microscopy analysis results of @C).

[0019] Figure 4 The images are scanning electron microscope (SEM) images of two comparison samples. (a) to (c) are SEM images of comparison sample 1 at different magnifications; (d) is the SEM image of comparison sample 2.

[0020] Figure 5 Sample 1 (Si / SiO) x @C), Comparison Sample 1 (Si / SiO) x The electrochemical performance of Example 1 and Comparative Sample 2 (Si) is compared. Among them, (a) is the charge-discharge curve of Example 1; (b) is the charge-discharge curve of Comparative Sample 1; (c) is the charge-discharge curve of Comparative Sample 2; and (d) is a comparison of the cycle performance of the three samples. Detailed Implementation

[0021] The present invention will be further described in detail below through specific embodiments. Example 1

[0022] This embodiment provides a capsule-structured Si / SiO2 x The preparation method of @C in-situ nanocomposite wire bundles includes the following steps: (1) Preparation of reaction mixture: Under stirring conditions, concentrated ammonia (25 wt%) was added to 60 mL of zinc acetate solution (containing 4 mmol of zinc acetate) until the white precipitate just disappeared completely to obtain zinc ammonia complex solution; then 10 mL of sodium silicate solution (containing 5 mmol of sodium silicate) was added to the zinc ammonia complex solution to obtain reaction mixture; (2) Hydrothermal preparation of the precursor: The reaction mixture obtained in step (1) was transferred to a 100 mL reactor for the first hydrothermal reaction at a temperature of 195 °C for 12 h. After the reaction, the precipitate was centrifuged and dried to obtain the precursor. (3) Hydrothermal carbon coating treatment of precursor: Weigh 1 g of the precursor obtained in step (2), disperse it in 70 mL of glucose solution with a concentration of 30 mmol / L, place it in a 100 mL reaction vessel, heat it to 180 °C, carry out a second hydrothermal reaction for 12 h, and after the reaction is completed, centrifuge and dry the product to obtain carbon-coated precursor; (4) Magnesium reduction to prepare the target product: The carbon-coated precursor obtained in step (3) was mixed with magnesium powder and sodium chloride at a mass ratio of 1:1:10. Under the protection of argon atmosphere, the mixture was heated to 650 °C for magnesium reduction reaction for 3 h. After cooling, the product was acid washed, separated and dried to obtain capsule-structured Si / SiO. x @C in-situ nanocomposite wire bundle.

[0023] To verify the beneficial effects of the wire bundle morphology, nanowire capsule structure, and internal homogeneity achieved through in-situ reaction of the materials in this invention, the following comparative samples were used for performance testing in this embodiment: Comparative Sample 1: A Si / SiO without carbon coating x The preparation process of the nanowire bundle sample includes three steps: reaction mixture preparation, precursor preparation, and magnesothermic reduction. The parameters are the same as those in this embodiment. The only difference between the preparation process of this comparative sample and the sample in this embodiment is that after the precursor preparation is completed, magnesothermic reduction treatment is performed directly without hydrothermal carbon coating treatment. Comparison Sample 2: Commercialized nano-silicon powder.

[0024] Figure 1 The XRD patterns of the sample, control sample 1, and control sample 2 prepared in this embodiment are shown below. Figure 1 (a) and EDS analysis results ( Figure 1(b)). Based on the presence of Si and SiO in the XRD pattern. x Based on the diffraction peak characteristics of C or the elemental composition obtained from EDS analysis, it can be inferred that the sample in this embodiment consists of Si and SiO. x Composed of C, and compared to sample 1 which is composed of Si and SiO x The composition of the control sample 2 is mainly Si.

[0025] The scanning and transmission electron microscopy analysis results of the samples in this embodiment are as follows: Figure 2 , 3 As shown, the material exhibits a nanowire bundle structure with an overall length of approximately 10 μm, composed of ordered nanowires. The nanowires also exhibit a capsule structure, with an outer shell of a uniform, continuous, conformal carbon layer approximately 10 nm thick; the core consists of uniformly distributed Si nanoparticles and SiO₂. x The matrix consists of crystalline Si nanoparticles, approximately 10 nm in size, highly dispersed within amorphous continuous SiO₂. x Within the matrix. These results demonstrate that it is a capsule-structured Si / SiO₂ x @C in-situ nanocomposite wire bundle.

[0026] Comparison of the scanning electron microscope images of sample 1 as follows Figure 4 As shown in (a)~(c), it exhibits a nanowire bundle structure, but without a carbon layer coating, indicating that it is only a Si / SiO2 type. x Nanowire bundle materials.

[0027] The scanning electron microscope image of the comparison sample 2 (nano-silicon powder) is as follows: Figure 4 (d) The figure shows the morphology of conventional nanoparticles, which are about 30 nm in size and exhibit obvious aggregation.

[0028] The capsule structure Si / SiO in this embodiment x@C in-situ nanocomposite wire bundles were mixed with polyvinylidene fluoride (PVDF) and acetylene black in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was added and stirred until homogeneous, forming a slurry. This slurry was then coated onto a copper foil current collector, vacuum dried, and die-cut into discs to serve as the working electrodes. Test batteries were assembled in a glove box protected by high-purity argon gas. A lithium metal disc was used as the counter electrode, and a 1 mol / L LiPF6 solution of ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) (volume ratio 1:1:1) was used as the electrolyte. A Celgard 2400 polypropylene (PP) membrane was used as the separator. Constant current charge-discharge tests were conducted at 25 °C, within a voltage range of 0.02–1.5 V, and at a current density of 0.1 A / g to evaluate the material's initial reversible capacity, initial coulombic efficiency, and cycle stability. Comparative samples 1 and 2 were prepared using the same process for electrode fabrication and battery assembly, and their performance was tested under the same conditions.

[0029] A comparison of the charge-discharge curves and cycle performance of the three samples is as follows: Figure 5 As shown in Table 1, the specific values ​​of the initial reversible capacity, initial coulombic efficiency, and capacity retention after 200 cycles are presented. The sample in this embodiment exhibits significantly higher initial coulombic efficiency and cycle stability than Comparative Sample 1 and Comparative Sample 2, which is sufficient to demonstrate the enhancing effect of the material's bundled morphology, nanocapsule structure, and internal homogeneity achieved through in-situ reaction on electrochemical performance.

[0030] Table 1. Comparison of electrochemical performance of Sample 1 in Example 1 with Comparative Sample 1 and Comparative Sample 2 sample First reversible capacity (mAh / g) First Coulomb Efficiency (%) Capacity retention (%) after 200 cycles Example 1 Sample 1183 78.5 76.9 Comparison Sample 1 1290 69.2 17.5 Comparison Sample 2 1793 62.8 4.7 Example 2

[0031] This embodiment provides a capsule-structured Si / SiO2 x The preparation method of @C in-situ nanocomposite wire bundles includes the following steps: (1) Preparation of reaction mixture: Under stirring conditions, concentrated ammonia (25 wt%) was added to 60 mL of zinc acetate solution (containing 2 mmol of zinc acetate) until the white precipitate just disappeared completely to obtain zinc ammonia complex solution; then 10 mL of sodium silicate solution (containing 5 mmol of sodium silicate) was added to the zinc ammonia complex solution to obtain reaction mixture; (2) Hydrothermal preparation of the precursor: The reaction mixture obtained in step (1) was transferred to a 100 mL reactor for the first hydrothermal reaction at a temperature of 185 °C for 9 h. After the reaction, the precipitate was centrifuged and dried to obtain the precursor. (3) Hydrothermal carbon coating treatment of precursor: Weigh 1 g of the precursor obtained in step (2), disperse it in 70 mL of glucose solution with a concentration of 20 mmol / L, place it in a 100 mL reaction vessel, heat it to 170 °C, carry out a second hydrothermal reaction for 10 h, and after the reaction is completed, centrifuge and dry the product to obtain carbon-coated precursor; (4) Magnesium reduction to prepare the target product: The carbon-coated precursor obtained in step (3) was mixed with magnesium powder and sodium chloride in a mass ratio of 1:1:5. Under nitrogen atmosphere protection, the mixture was heated to 700 °C for magnesium reduction reaction for 2.5 h. After cooling, the product was acid washed, separated and dried to obtain capsule-structured Si / SiO. x @C in-situ nanocomposite wire bundle.

[0032] The capsule structure Si / SiO prepared in this embodiment x @C in-situ nanocomposite wire bundle has an initial capacity of 1100 mAh / g, an initial coulombic efficiency of 73.5%, and a reversible capacity retention of 70.2% after 200 cycles. Example 3

[0033] This embodiment provides a capsule-structured Si / SiO2 x The preparation method of @C in-situ nanocomposite wire bundles includes the following steps: (1) Preparation of reaction mixture: Under stirring conditions, concentrated ammonia (25 wt%) was added to 60 mL of zinc acetate solution (containing 6 mmol of zinc acetate) until the white precipitate just disappeared completely to obtain zinc ammonia complex solution; then 10 mL of sodium silicate solution (containing 5 mmol of sodium silicate) was added to the zinc ammonia complex solution to obtain reaction mixture; (2) Hydrothermal preparation of the precursor: The reaction mixture obtained in step (1) was transferred to a 100 mL reactor for the first hydrothermal reaction at a temperature of 215 °C for 15 h. After the reaction, the precipitate was centrifuged and dried to obtain the precursor. (3) Hydrothermal carbon coating treatment of precursor: Weigh 1 g of the precursor obtained in step (2), disperse it in 70 mL of glucose solution with a concentration of 50 mmol / L, place it in a 100 mL reaction vessel, heat it to 200 °C, carry out a second hydrothermal reaction for 16 h, and after the reaction is completed, centrifuge and dry the product to obtain carbon-coated precursor; (4) Magnesium reduction to prepare the target product: The carbon-coated precursor obtained in step (3) was mixed with magnesium powder and sodium chloride at a mass ratio of 1:2:15. Under the protection of an argon-hydrogen mixture (containing 5 vol% hydrogen), the mixture was heated to 750 °C for magnesium reduction reaction for 4 h. After cooling, the product was acid washed, separated, and dried to obtain Si / SiO. x @C in-situ nanocomposite wire bundle.

[0034] The capsule structure Si / SiO prepared in this embodiment x The @C in-situ nanocomposite wire bundle has an initial capacity of 1526 mAh / g, an initial coulombic efficiency of 71.8%, and a reversible capacity retention of 52.7% after 200 cycles.

Claims

1. A capsule structure Si / SiO x The method for preparing @C in-situ nanocomposite wire bundles is characterized by, Includes the following steps: (1) Preparation of reaction mixture: Under stirring conditions, concentrated ammonia water is added to zinc acetate solution until the white precipitate just disappears completely to obtain zinc ammonia complex solution; then sodium silicate solution is added to the zinc ammonia complex solution to obtain reaction mixture; (2) Hydrothermal preparation of precursor: The reaction mixture obtained in step (1) is placed in a reaction vessel for the first hydrothermal reaction. After the reaction is completed, the precipitate is centrifuged and dried to obtain the precursor. (3) Hydrothermal carbon coating treatment of precursor: The precursor obtained in step (2) is dispersed in glucose solution and placed in a reaction vessel for a second hydrothermal reaction. After the reaction is completed, the product is centrifuged and dried to obtain carbon-coated precursor. (4) Magnesium reduction to prepare the target product: The carbon-coated precursor obtained in step (3) is mixed evenly with magnesium powder and sodium chloride. Under a protective atmosphere, the mixture is heated to carry out a magnesium reduction reaction. The resulting product is acid washed, separated, and dried to obtain a capsule-structured Si / SiO2. x @C in-situ nanocomposite wire bundle.

2. The preparation method according to claim 1, characterized in that, The molar ratio of zinc acetate and sodium silicate in step (1) is (2~6):

5.

3. The preparation method according to claim 1, characterized in that, The temperature of the first hydrothermal reaction in step (2) is 180~220 ℃ and the time is 8~16 h.

4. The preparation method according to claim 1, characterized in that, The concentration of the glucose solution in step (3) is 15~50 mmol / L; the temperature of the second hydrothermal reaction is 160~200 ℃, and the time is 8~16 h.

5. The preparation method according to claim 1, characterized in that, In step (4), the mass ratio of the carbon-coated precursor to magnesium powder and sodium chloride is 1:(1~2):(5~15); the protective atmosphere is argon or an argon-hydrogen mixture; the heating temperature of the magnesium thermal reduction reaction is 650~750℃, and the reaction time is 2~4 h.

6. A capsule-structured Si / SiO2 prepared by the preparation method according to any one of claims 1 to 5 x @C in-situ nanocomposite wire bundle.

7. The capsule-structured Si / SiO2 obtained by the preparation method according to any one of claims 1 to 5 x Application of @C in-situ nanocomposite wire bundles in the preparation of lithium-ion battery anode materials.

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