An ultrafine silicon-carbon composite material based on in-situ electrochemical induction and its preparation method and application

Abstract

The present invention provides an ultrafine silicon-carbon composite material based on in-situ electrochemical induction, and its preparation method and application. The method comprises: (1) cleaning, ball milling, and etching a silicon wafer to obtain a nano-silicon wafer; (2) carbonizing the wafer with a carbon source to form carbon-coated silicon particles; (3) assembling a battery with the composite material as the negative electrode, inducing the silicon to form an ultrafine silicon network with a diameter of 2-20nm by electrochemical in-situ induction, and simultaneously infiltrating the carbon into the pores of the silicon network to form a double continuous interpenetrating structure. The structure can achieve good performance as a negative electrode for lithium-ion batteries, and its embodiment has a 0.2Ag ‑1 The first cycle specific capacity reaches 1635mAhg ‑1 , 95% capacity retention after 100 cycles, and 98.4% capacity retention after 50 cycles of the full battery. This invention avoids the high-cost ultrafine silicon preparation process, is compatible with industrial mass production, and can be used as a negative electrode active material to make high-capacity lithium-ion batteries for use in building energy storage units for marine floating platforms, deep-sea monitoring equipment, or island microgrids.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterials and electrochemical devices, and in particular to an ultrafine silicon-carbon composite material based on in-situ electrochemical induction, a preparation method thereof, and applications thereof. Background Art

[0002] Silicon has a high theoretical capacity (3580mAhg -1 ) is considered as the core candidate for the next generation of lithium-ion battery anode materials, but its commercialization still faces two major bottlenecks: First, the drastic volume change (>300%) during lithium insertion / extraction causes electrode pulverization, active material shedding, and continuous rupture and regeneration of the SEI film, which intensifies the electrolyte side reaction and lithium loss, leading to rapid capacity decay; second, the low intrinsic conductivity (~10 -3 Sm -1 ) limits electron transport, resulting in severe polarization and low capacity utilization at high rates. To alleviate these issues, silicon nanomaterials (such as nanowires and porous structures) can shorten ion diffusion paths and buffer mechanical stress, with the smaller the size, the more significant the effect. However, pure nanosilicon is prone to uncontrollable aggregation and SEI penetration due to dynamic stress during cycling, forming electrochemically inert "dead silicon." Therefore, the composite of nanosilicon and carbon (such as graphene and carbon nanotube coating) has become an effective strategy to improve conductivity and suppress volume expansion.

[0003] Currently, nano-silicon / carbon composites have a variety of structures. However, the interfacial bonding of traditional carbon composites is mostly physical mixing or simple coating. The synergistic effect between silicon and carbon during cycling is insufficient, and the carbon layer is easily ruptured by silicon expansion. Due to the weak interfacial bonding between silicon and carbon, it is eroded by the SEI, making it unable to dynamically adapt to volume changes. Researchers have also developed various methods to prepare silicon / carbon composites, such as ball milling, thermal reduction, dealloying, and chemical etching. However, these preparation techniques all directly produce nano-silicon structures, and the sizes generally produced are above 100 nm, making it difficult to produce ultrafine nano-silicon (e.g., <30 nm). Chemical vapor deposition (CVD) is a popular method for directly producing ultrafine nano-silicon through the decomposition of silane. It is efficient and the size of the prepared materials can be controlled, but its high cost has limited its development.

[0004] In summary, existing silicon-carbon composite materials have difficulty balancing high capacity and cycle stability due to limitations in preparation technology and structural design. They mainly have the following defects:

[0005] 1. Ultrafine structures (e.g. <30nm) are difficult to prepare, and high energy consumption and high cost processes significantly increase costs.

[0006] 2. The lack of stable silicon / carbon composites, simple coating or physical mixing, weak interface bonding between silicon and carbon, isolated distribution, and the interface between silicon and carbon is easily corroded by SEI, resulting in the breakage of the electron conduction path and performance degradation.

[0007] Therefore, it is necessary to develop a relatively simple silicon / carbon composite strategy to achieve the preparation of stable ultrafine silicon / carbon composite structures, so that they can achieve good electrochemical performance as the negative electrode of lithium-ion batteries. Summary of the Invention

[0008] In view of this, the present invention proposes an ultrafine silicon-carbon composite material based on in-situ electrochemical induction, and its preparation method and application, which self-assembles an ultrafine silicon / carbon interpenetrating network during the cycle through in-situ electrochemical induction. The present invention utilizes the spontaneous refinement of silicon and the dynamic penetration of carbon induced in situ during the electrochemical cycle to directly form an ultrafine nanoscale interpenetrating network, constituting a network connecting branches of 2-20nm. There is no need to prepare an ultrafine structure before the electrochemical cycle, and no high-cost ultrafine nano-process is required. This stable silicon / carbon three-dimensional interpenetrating structure forms a bicontinuous structure of ultrafine silicon and carbon, which achieves good cycle stability as a lithium-ion battery. This strategy converts the electrochemically driven silicon / carbon structural evolution into a structural optimization driving force, achieves a stable ultrafine structure with a low-cost process, and breaks through the bottleneck of silicon-based negative electrode industrialization.

[0009] The technical solution of the present invention is achieved as follows: a method for preparing an ultrafine silicon-carbon composite material based on in-situ electrochemical induction, comprising the following steps:

[0010] (1) Silicon pretreatment: The silicon wafer was ultrasonically cleaned in 0.2-0.5 wt% dilute hydrochloric acid solution, deionized water, and anhydrous ethanol for 1-1.2 hours, respectively, and then ball-milled and etched with 2-4% wt% hydrofluoric acid for 1-3 hours. The silicon wafer was then vacuum filtered and dried to obtain silicon nanosheets.

[0011] (2) Carbon composite: The silicon nanosheets obtained in step (1) were mixed with a carbon source at a mass volume ratio of 3-5 g:100 mL, and carbonized at 700-900 °C for 1-3 hours under an inert atmosphere to form carbon-coated silicon particles (pSi@C);

[0012] (3) Electrochemical induction: Carbon-coated silicon particles (pSi@C) are used as the negative electrode to assemble the battery. The voltage range is 0.01-1.5V and the charge is 0.2-1.0Ag. -1 The battery was charged and discharged for three cycles at a current density of 100 nm. The carbon matrix penetrated into the silicon pores through topological rearrangement, forming an in-situ silicon-carbon interpenetrating bicontinuous structure, which is an ultrafine silicon-carbon composite material. In-situ electrochemical induction is the direct induction into an ultrafine network structure during the previous cycle of the battery, rather than preparing the nanostructure in the electrolytic cell and then assembling it into the battery.

[0013] Furthermore, the silicon wafer in step (1) is a waste photovoltaic silicon wafer.

[0014] Furthermore, in step (1), the ball milling speed is 300-500 rpm, and the ball milling is performed for 5-7 hours.

[0015] Furthermore, the silicon nanosheets in step (1) have a thickness of about 100 nm and a width of micrometer level.

[0016] Furthermore, the carbon source in step (2) is an aqueous solution of sucrose or maltodextrin at a concentration of 0.03-0.05 g / mL, which is spray-dried and then carbonized.

[0017] Furthermore, the inert atmosphere in step (2) is argon or nitrogen.

[0018] Furthermore, the electrochemically induced current density in step (3) is 0.2Ag -1 , 0.5Ag -1 or 1.0Ag -1 .

[0019] Furthermore, the preparation method produces an ultrafine silicon-carbon composite material, the structure of which comprises:

[0020] Silicon phase: An ultrafine silicon network composed of nano-ligaments, where the diameter of the nano-ligaments is 2-20nm;

[0021] Carbon phase: The carbon source penetrates into the pores of the silicon network through topological rearrangement, forming carbon-filled nanochannels;

[0022] The silicon phase and carbon interpenetrate with each other to form a double continuous nano-network of silicon-encapsulated carbon and carbon-embedded silicon.

[0023] Furthermore, the ultrafine silicon-carbon composite material is used as a negative electrode active material in a lithium-ion battery system.

[0024] Furthermore, the lithium-ion battery system is used as an energy storage unit for an ocean floating platform, deep-sea monitoring equipment, or an island microgrid.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The present invention achieves low-cost and high-efficiency preparation of ultrafine silicon-carbon interpenetrating network structures through in-situ electrochemically induced self-assembly strategy. Its core advantages are reflected in the following aspects:

[0027] (2) Ultrafine structures do not require direct preparation, which is expected to significantly reduce costs. Traditional methods rely on high-energy mechanical ball milling or dangerous silane processes to prepare ultrafine silicon (<30nm). However, the present invention spontaneously drives silicon refinement through electrochemical cycling (ligament diameter after cycling is 2-20nm), eliminating the need for direct preparation of ultrafine nanostructures.

[0028] (3) In situ electrochemically induced interpenetrating network structure. Silicon and carbon circulate within a closed carbon structure to form a three-dimensional bicontinuous interpenetrating network. This structure requires a specific silicon-carbon composite structure, with carbon encapsulating the outside and carbon filling the gaps inside to encapsulate silicon particles. Simple carbon-encapsulated silicon and silicon-carbon mixtures cannot form this structure through electrochemical induction.

[0029] (3) The structure produced by this method can achieve excellent cycling stability. After the electrochemical induction process, it can maintain a high coulombic efficiency (99.9%), and the full battery matching LiFePO4 can also achieve good performance. However, materials that cannot form an ultrafine network structure through the induction process show poor cycling performance. This proves that this structure has good performance as a negative electrode for lithium-ion batteries.

[0030] This method is industrially compatible. Spray drying and carbonization processes are compatible with existing lithium battery production lines, enabling mass production. High-energy ball milling and silane processing are not required.

[0031] In summary, the present invention designs a specific silicon-carbon composite structure and induces an ultrafine silicon / carbon network interpenetrating structure through in-situ electrochemical induction, thereby achieving a high-capacity, long-life silicon-based negative electrode with a low-cost process, which is expected to provide an innovative solution for breakthroughs in the energy density and cycle life of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The morphology of the final samples prepared in Example 1, Example 2, Comparative Example 1, and Comparative Example 2;

[0033] Figure 2 The dark field image (HAADF), bright field image (ABF), and energy dispersive spectrometer (EDS) before electrochemical induction obtained in Example 1 are shown;

[0034] Figure 3 The HAADF / ABF diagram and EDS spectrum diagram after electrochemical induction in Example 1;

[0035] Figure 4 This is a high-resolution HAADF / ABF image after electrochemical induction in Example 1;

[0036] Figure 5 3D reconstructed slice images based on HAADF before and after electrochemical induction in Example 1;

[0037] Figure 6 3D reconstruction images before and after electrochemical induction and contrast-based Si / C volume segmentation of Example 1;

[0038] Figure 7 This is the HAADF / ABF diagram after electrochemical induction in Example 2;

[0039] Figure 8 This is the HAADF / ABF diagram after electrochemical induction in Example 3;

[0040] Figure 9 This is the HAADF / ABF diagram after electrochemical induction in Example 4;

[0041] Figure 10 This is the HAADF / ABF diagram after electrochemical induction of Comparative Example 1;

[0042] Figure 11 This is the HAADF / ABF diagram after electrochemical induction of Comparative Example 2;

[0043] Figure 12 The lithium half-cells of Examples 1-4 and Comparative Examples 1-2 after electrochemical induction at 0.2Ag -1 Cycling performance under

[0044] Figure 13 Specific capacity-voltage curve during the electrochemical induction process in Example 1;

[0045] Figure 14 This is the cycling performance of the sample in Example 1 for the full battery of lithium iron phosphate at 0.2C. DETAILED DESCRIPTION

[0046] In order to better understand the technical content of the present invention, specific examples are provided below to further illustrate the present invention.

[0047] Unless otherwise specified, the experimental methods used in the examples of the present invention are all conventional methods.

[0048] Unless otherwise specified, the materials, reagents, etc. used in the examples of the present invention can be obtained from commercial sources.

[0049] Example 1

[0050] The preparation method of ultrafine silicon-carbon composite material based on in-situ electrochemical induction comprises the following steps:

[0051] (1) Silicon wafer pretreatment: Waste photovoltaic silicon wafers were ultrasonically cleaned with 0.3 wt% HCl, ethanol, and deionized water for 1 hour. The silicon wafers were ball milled at 400 rpm for 6 hours and then etched with 3 wt% hydrofluoric acid for 2 hours. The mixture was separated by vacuum filtration and dried.

[0052] (2) Carbon composite: 4 g of treated silicon was dispersed in 100 ml of 0.04 g / mL sucrose aqueous solution and carbonized at 800 °C for 2 h in a N2 atmosphere to form carbon-coated silicon particles.

[0053] (3) Electrochemical induction: pSi@C was used as the negative electrode to assemble the battery.-1 The device was charged and discharged for three cycles in the voltage range of 0.01-1.5V, and silicon and carbon were recombined through electrochemical induction to form an ultrafine silicon-carbon interpenetrating structure.

[0054] Example 2

[0055] The sucrose aqueous solution in step 2 was replaced with a 0.04 g / mL maltodextrin aqueous solution.

[0056] The remaining steps are the same as in Example 1.

[0057] Example 3

[0058] The electrochemical induction process in step 3 was carried out at 0.5Ag -1 Charge and discharge cycle 3 times.

[0059] The remaining steps are the same as in Example 1.

[0060] Example 4

[0061] The electrochemical induction process in step 3 is carried out at 1.0Ag -1 Charge and discharge cycle 3 times.

[0062] The remaining steps are the same as in Example 1.

[0063] Comparative Example 1

[0064] The difference from Example 1 is that in step 2, the carbon source is replaced with pitch-derived carbon.

[0065] The specific steps are as follows:

[0066] 4 g of treated silicon and 4 g of asphalt were mixed, pressurized at 20 MPa in a mold for 5 minutes, pressed into sheets, and carbonized at 800°C for 2 hours in a N2 atmosphere to form asphalt-derived carbon-coated silicon particles.

[0067] The remaining steps are the same as in Example 1.

[0068] Comparative Example 2

[0069] The difference from Example 1 is that in the silicon wafer pretreatment process in step 1, the morphology and size of the silicon are inconsistent and are at the submicron level. The specific steps are as follows:

[0070] The waste photovoltaic silicon wafers were ultrasonically cleaned with 0.3 wt% HCl, ethanol and deionized water for 1 hour in sequence; the silicon was ball milled at a speed of 200 rpm for 6 hours and taken out for use.

[0071] The remaining steps are the same as in Example 1.

[0072] Ultrafine structure characterization:

[0073] Figure 1From left to right are the sample morphologies of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 before electrochemical induction. The carbon sources used in Example 1, Example 2, and Comparative Example 1 are sucrose-derived carbon, maltodextrin-derived carbon, and pitch-derived carbon, respectively. The silicon sizes of Comparative Example 2 and Example 1 are different. Judging from the size of the exposed silicon, some silicon particles in Comparative Example 2 can reach the micron level, while the silicon morphology in Example 1 is silicon nanosheets with a relatively small size and a thickness of about 100 nm ( Figure 2 ).also, Figure 2 It also shows that the two-dimensional silicon nanosheets in Example 1 are uniformly dispersed in the carbon and wrapped by the carbon before electrochemical induction. Figure 3 This shows that after electrochemical induction in Example 1, the silicon structure is obviously transformed from a thin sheet structure to a finer network structure. Figure 4 The fine network structure of Example 1 is more clearly shown, and the smallest connecting branches in the silicon network can reach 2nm. At the same time, according to the contrast between the bright and dark field images, it can be seen that carbon is still wrapped and interspersed in the silicon network structure. Figure 5 Comparative Example 1 shows the refinement of the silicon network before and after electrochemical induction. Figure 6 This is the 3D reconstructed model of Example 1 based on HAADF images from multiple angles. Low-contrast carbon is stained green, while high-contrast silicon is stained orange (top two images). The silicon and carbon volumes are segmented based on contrast and shape, colored blue and gray (bottom two images). It can be seen that while silicon forms a fine network, its volume fluctuations during charge and discharge squeeze the carbon, causing the carbon to form fine networks interpenetrating within the silicon network, creating a silicon / carbon interpenetrating structure.

[0074] The structure of maltodextrin-derived carbon-wrapped silicon flakes can still generate an ultrafine silicon / carbon interpenetrating network structure after electrochemical induction ( Figure 7 ). Use a larger current of 0.5A -1 or 1.0Ag -1 After electrochemical induction, an ultrafine silicon / carbon interpenetrating network structure can also be formed ( Figure 8 , Figure 9 However, the structure of pitch-derived carbon wrapped silicon flakes is not the same, and after electrochemical induction, it still shows a large number of silicon flake structures ( Figure 10 If the silicon particles are large, even at the submicron or micron level, it will not work. After electrochemical induction, a large number of large-sized silicon particle structures will appear ( Figure 11 ). This shows that whether an ultrafine Si / C interpenetrating network can be formed is related to the carbon structure and Si particle size before electrochemical induction.

[0075] Electrochemical performance test:

[0076] Figure 12The performance of lithium half-cells of the examples and comparative examples is shown. It can be found that the material that can form an ultrafine silicon / carbon interpenetrating network structure after electrochemical induction can achieve good stability, while the material that cannot form the ultrafine network structure has a faster decay during the cycle. -1 The specific capacity reaches 1635mAhg -1 , the capacity retention rate after 100 cycles is 95%, and the performance of the remaining materials with ultrafine network structure is similar to that of Example 1. Figure 13 The specific capacity-voltage curves of the first and last cycles of the electrochemical induction process of Example 1 are shown, and its coulombic efficiency remains at the initial 81%. Considering the side reactions of the silicon negative electrode, the coulombic efficiency retention rate during this induction process is good. Figure 14 It shows that the material in Example 1 matches the full battery of commercial LiFePO4 electrode sheet (N / P=1.2) and the capacity increases from 142.0 mAh g to 142.0 mAh g after 50 cycles. -1 Decay to 139.7mAhg -1 , the capacity retention rate is as high as 98.4%.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing ultrafine silicon-carbon composite materials based on in-situ electrochemical induction, characterized in that: The following steps are involved: (1) Silicon wafer pretreatment: The silicon wafer was ultrasonically cleaned in 0.2-0.5wt% dilute hydrochloric acid solution, deionized water, and anhydrous ethanol for 1-1.2 hours respectively, ball-milled and etched with 2-4%wt% hydrofluoric acid for 1-3 hours, vacuum filtered and dried to obtain silicon nanosheets; (2) Carbon composite: The silicon nanosheets obtained in step (1) were mixed with a carbon source at a mass volume ratio of 3-5g:100mL, and carbonized at 700-900℃ for 1-3 hours under an inert atmosphere to form carbon-coated silicon particles; (3) Electrochemical induction: The carbon-coated silicon particles were used as the negative electrode to assemble the battery, and the battery was charged with 0.2-1.0Ag in the voltage range of 0.01-1.5V. -1 The battery was charged and discharged for three cycles at a current density of 100 nm to form an in-situ silicon-carbon interpenetrating double continuous structure, which is an ultrafine silicon-carbon composite material.

2. The method for preparing an ultrafine silicon-carbon composite material based on in-situ electrochemical induction according to claim 1, characterized in that: The silicon wafers in step (1) are waste photovoltaic silicon wafers.

3. The method for preparing an ultrafine silicon-carbon composite material based on in-situ electrochemical induction according to claim 1, characterized in that: In step (1), the ball milling speed is 300-500 rpm, and the ball milling is performed for 5-7 hours.

4. The method for preparing an ultrafine silicon-carbon composite material based on in-situ electrochemical induction according to claim 1, characterized in that: The thickness of the silicon nanosheet in step (1) is ≤100 nm.

5. The method for preparing an ultrafine silicon-carbon composite material based on in-situ electrochemical induction according to claim 1, characterized in that: The carbon source in step (2) is an aqueous solution of sucrose or maltodextrin with a concentration of 0.03-0.05 g / mL, which is spray-dried and then carbonized.

6. The method for preparing an ultrafine silicon-carbon composite material based on in-situ electrochemical induction according to claim 1, characterized in that: The inert atmosphere in step (2) is argon or nitrogen.

7. The method for preparing an ultrafine silicon-carbon composite material based on in-situ electrochemical induction according to claim 1, characterized in that: The electrochemically induced current density in step (3) is 0.2Ag -1 , 0.5Ag -1 or 1.0Ag -1 .

8. An ultrafine silicon-carbon composite material obtained by the preparation method according to any one of claims 1 to 7, characterized in that: Its structure includes: Silicon phase: An ultrafine silicon network composed of nano-ligaments, where the diameter of the nano-ligaments is 2-20nm; Carbon phase: infiltrates into the pores of the silicon network through topological rearrangement, forming carbon-filled nanochannels; The silicon phase and carbon interpenetrate with each other to form a double continuous nano-network of silicon-encapsulated carbon and carbon-embedded silicon.

9. The use of the ultrafine silicon-carbon composite material according to claim 8, characterized in that: The ultrafine silicon-carbon composite material is used as a negative electrode active material in a lithium-ion battery system.

10. The use according to claim 9, characterized in that The lithium-ion battery system is used as an energy storage unit for an ocean floating platform, deep-sea monitoring equipment, or an island microgrid.

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