A carbon-interpenetrated ultrafine silicon network composite material and its preparation method and application

Abstract

The present invention discloses a preparation method and application of a carbon interlaced ultrafine silicon network composite structure. The method uses a low specific surface area carbon skeleton as a carrier, and after high-temperature air oxidation pretreatment, nano-silicon particles are loaded by vapor deposition or mixing method, and the battery is assembled for in-situ electrochemical induction. During the induction process, the silicon particles undergo "lithiation fusion-delithiation bonding" to form a continuous network, and the carbon phase is interlaced therein to limit silicon agglomeration, thereby obtaining a two-phase interlaced structure with a silicon network skeleton size of 5-40nm. The embodiment thereof is used as a negative electrode of a lithium-ion battery at 0.2Ag ‑1 The specific capacity reaches 1507mAhg ‑1 The capacity retention rate after 100 cycles is 94.8%, while the capacity retention rate of a full LiFePO4 battery after 50 cycles is 98.1%. This invention eliminates the high cost of porous carbon carriers, solves the problems of nano-silicon agglomeration and side reactions, and is compatible with industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterials and electrochemical devices, and in particular to a method for preparing a low-cost in-situ electrochemically induced carbon-intercalated ultrafine silicon composite structure and its application as a negative electrode material for lithium-ion batteries. Background Art

[0002] Lithium-ion batteries used in energy storage units for building ocean floating platforms, deep-sea monitoring equipment, or island microgrids usually use silicon as the negative electrode material. -1 The ultra-high theoretical capacity of lithium-ion batteries is considered to be the core material of the next generation of lithium-ion batteries, but industrialization still faces multiple obstacles. First, the drastic volume change (>300%) during lithium insertion / extraction causes electrode pulverization and active material shedding, resulting in rapid capacity decay; second, the low intrinsic conductivity (~10 -3 Sm -1 ) limits electron transport, resulting in severe polarization and low capacity utilization under high-power discharge and fast-charge conditions. Nanoscaling silicon (e.g., nanowires, porous structures) and combining it with carbon materials has been shown to achieve good performance.

[0003] Among the methods for preparing silicon-carbon composite materials, preparing silicon-carbon composite materials on carbon materials (graphite, carbon fiber, etc.) by chemical vapor deposition of silane is considered to be an effective method, which can achieve the preparation of smaller sizes (2nm-100nm), and the size can be precisely controlled by changing the conditions. At present, the preparation of porous carbon to deposit silicon particles in the pores of carbon is considered to be an effective method. These carbon materials often need to have a high specific surface area and a large number of mesopores. For example, high specific surface area porous carbon (>500m2) can be prepared by KOH activation, template method, or CO2 oxidation. 2 g -1 ), but this type of process has problems such as highly corrosive reagent loss equipment, template removal, and high energy consumption. More importantly, the high specific surface area carrier causes excessive decomposition of the electrolyte, making the initial efficiency usually less than 80%, and the silicon deposition easily blocks the pores and reduces the capacity utilization. On the other hand, ultrafine silicon particles (such as 20-60nm) themselves have inherent defects: their specific surface area increases sharply to 100m 2 g -1 The surface is easily oxidized, and the continuous exposure of newly formed silicon during cycling triggers violent side reactions, significantly reducing Coulombic efficiency. Furthermore, excessive amounts of nano-silicon on the carbon surface can cause uncontrolled aggregation under dynamic stress, forming "dead silicon" encased in a thick SEI, leading to rapid capacity decay.

[0004] In summary, the composite of high specific surface area porous carbon and ultrafine silicon nanoparticles has the following main defects:

[0005] 1. Porous carbon is difficult to prepare. Silicon nanoparticles easily clog pores and are difficult to prepare in large quantities in the pores. High energy consumption and complex processes increase costs.

[0006] 2. High specific surface area carbon and high specific surface area silicon particles tend to lead to low coulombic efficiency.

[0007] 3. Excessive presence of nano-silicon on the silicon surface causes uncontrollable agglomeration under dynamic stress, which is easily corroded by SEI, forming "dead silicon" and causing performance degradation.

[0008] In order to overcome the above limitations, it is urgent to develop an innovative strategy that can avoid the complex preparation of porous carbon and inhibit the agglomeration and side reactions of nano-silicon. Summary of the Invention

[0009] In response to the three major challenges in the background technology, the present invention proposes a new method for electrochemically induced ultrafine silicon network polymerization. Its core innovation is to abandon the preparation of porous carbon supports and instead use a low specific surface area carbon skeleton (<50m 2 g -1 ) such as directly loading ultrafine silicon particles onto broken graphene sheets or carbon black aggregates, and then converting the physically contacted silicon particles into a covalently bonded network structure through a specific electrochemical process. The key mechanism of this method involves a two-stage evolution: During the low-voltage platform lithiation process, lithium-rich Li is formed on the surface of the silicon particles. x The Si phase, under conditions of expansion stress, compression, and lithiation, promotes fusion at the interfaces of adjacent particles. The subsequent delithiation stage triggers diffusion and rearrangement of silicon atoms, forming bonds at the junctions. Simultaneously, the presence of carbon spatially restricts silicon fusion and intersperses the silicon network, separating it into connecting branches 5-40nm in size, effectively inhibiting long-range aggregation. This structural material, with carbon interspersed in an ultrafine silicon network, achieves excellent electrochemical performance as a lithium-ion battery negative electrode, making it an ideal energy storage battery for applications such as building floating ocean platforms, deep-sea monitoring equipment, or island microgrids.

[0010] The technical solution of the present invention is achieved as follows:

[0011] A method for preparing a carbon-interpenetrated ultrafine silicon network composite material comprises the following steps:

[0012] (1) Carbon skeleton pretreatment: reduce the specific surface area to <30m 2 g -1 The carbon material is heat-treated in air at 300-400°C for 2-3 hours to oxidize the carbon skeleton;

[0013] (2) Silicon composite: Silicon particles are loaded on the carbon skeleton to obtain a composite;

[0014] (3) Electrochemical induction: Assemble the battery with the composite as the negative electrode and conduct the electrochemical induction with 0.2-1.0Ag in the voltage range of 0.01-1.5V. -1 The current density is cycled 3-4 times to induce the formation of a carbon-interpenetrating ultrafine silicon network composite material.

[0015] Furthermore, the carbon material is carbon black aggregate or carbon fiber.

[0016] Furthermore, silicon particles are loaded on the carbon skeleton by a deposition method or a mixing method.

[0017] Furthermore, the particle size of the silicon particles is 20-30 nm; and the loading amount of the silicon particles is 40 wt%-45 wt%.

[0018] Furthermore, when silicon particles are loaded on the carbon skeleton by vapor deposition, the silicon concentration volume fraction is controlled to be 10%-12%, and the deposition time is 40-45 minutes.

[0019] Furthermore, when silicon particles are loaded on the carbon skeleton by a mixing method, high-energy ball milling is performed at a rotation speed of 300-400 rpm / min for 4-5 hours, and the particles are dispersed in an aqueous solution with a solid content of 10-12 wt% and spray-dried.

[0020] Furthermore, the electrochemically induced current density is 0.2Ag -1 or 1.0Ag -1 .

[0021] Furthermore, the size of the silicon connecting branches of the carbon-interpenetrating ultrafine silicon network composite material is 5-40 nm.

[0022] Furthermore, the present invention prepares or purchases various carbon skeletons such as carbon black aggregates and carbon fibers. Carbon fibers are prepared by electrospinning. Carbon black aggregates are purchased directly.

[0023] Furthermore, in step (1), the carbon material is subjected to a high-temperature treatment in air to moderately oxidize it in order to create defects on the carbon surface. During the electrochemical induction process, the lithiated silicon and carbon can achieve ion-dipole interaction, thereby achieving close adhesion between the silicon and carbon. If other treatments have similar functions, they are also within the scope of protection of this patent.

[0024] Furthermore, in step (2), the carbon sources that can produce an ultrafine silicon network are carbon fibers and carbon black aggregates. However, multilayer graphene cannot. This means that the formation of an ultrafine silicon network is related to the carbon structure before electrochemical induction. For carbon black aggregates, whether silicon particles are deposited on the surface or mixed, they can be electrochemically induced into a porous silicon network structure.

[0025] Furthermore, the electrochemical induction scheme in step (3) is to-1 , 0.5Ag -1 In the next cycle, after three cycles of electrochemical induction, an ultrafine network structure interspersed with carbon matrix was formed.

[0026] Furthermore, the electrochemical induction scheme in step (3) is in situ electrochemical induction, which is to directly induce the ultrafine network structure during the previous cycle of the battery, rather than preparing the nanostructure in other electrolytic cells and then assembling it into the battery like other schemes.

[0027] Furthermore, during the induction process, silicon particles undergo "lithiation fusion-delithiation bonding" to form a continuous network, in which the carbon phase is interspersed to limit silicon agglomeration, obtaining a two-phase interlaced structure with a silicon connecting branch size of 5-40nm.

[0028] The carbon intercalated ultrafine silicon network composite material prepared by the preparation method of the present invention comprises a continuous silicon network with carbon intercalated, silicon particles connected by non-interfacial bonding and silicon connecting branches with a size of 5-40nm.

[0029] Application of the carbon interpenetrating ultrafine silicon network composite material prepared by the preparation method of the present invention in the preparation of negative electrode materials for lithium ion batteries.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] This invention achieves low-cost and efficient preparation of carbon-interpenetrated ultrafine silicon network structures through an in-situ electrochemically induced self-assembly strategy. Its core advantages are reflected in the following aspects:

[0032] 1. In situ electrochemically induced carbon interpenetration into an ultrafine silicon network structure. This ultrafine silicon network structure eliminates the need for direct fabrication, potentially significantly reducing costs. This eliminates the need for porous carbon preparation, reducing costs and increasing efficiency. This invention uses electrochemical cycling to spontaneously drive the formation of a network of nanosilicon nanostructures (ligament diameter 5-40 nm after cycling), with carbon interpenetrating within. This interpenetration prevents aggregation and electrical isolation of the silicon network.

[0033] 2. Surface oxidation of carbon enhances adhesion to silicon, inhibiting the aggregation of nano-silicon. After electrochemical induction, carbon nano-silicon and carbon form a three-dimensional bicontinuous interpenetrating topology. Silicon particles adhere to defective carbon and undergo "lithiation fusion and delithiation bonding," transforming discrete particles into a network structure.

[0034] 3. The structure produced by this method achieves excellent cycling stability. After the electrochemical induction process, the carbon-intercalated silicon network maintains a high coulombic efficiency (average 99.9%) and achieves good performance in full-cell LiFePO4 batteries. Materials that fail to form an ultrafine network through the induction process exhibit poor cycling performance. This demonstrates the excellent performance of this structure as a lithium-ion battery anode.

[0035] 4. This method is industrially compatible. Processes such as vapor deposition and in-situ electrochemical induction are compatible with existing lithium battery production lines, making it easy to achieve mass production.

[0036] In summary, the present invention designs a specific silicon-carbon composite structure and uses in-situ electrochemical induction to form a carbon-interpenetrated ultrafine silicon network structure material, 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

[0037] Figure 1 These are SEM images of carbon black aggregates, carbon fibers, and multilayer graphene.

[0038] Figure 2 is a SEM image of vapor deposited silicon.

[0039] Figure 3 This is the HAADF / ABF diagram of Example 1 before electrochemical induction.

[0040] Figure 4 This is a high-resolution HAADF / ABF image of Example 1 before electrochemical induction.

[0041] Figure 5 This is a high-resolution HAADF / ABF image after the first discharge during the electrochemical induction process of Example 1.

[0042] Figure 6 This is the HAADF / ABF diagram after electrochemical induction in Example 1.

[0043] Figure 7 This is the high-resolution HAADF / ABF image after electrochemical induction and the atomic image of the particle bonding site in Example 1.

[0044] Figure 8 It is the HAADF diagram after electrochemical induction and the EDS energy spectrum diagram of element distribution in Example 1.

[0045] Figure 9 This is the HAADF / ABF diagram after electrochemical induction in Example 2.

[0046] Figure 10 This is the HAADF / ABF diagram after electrochemical induction in Example 3.

[0047] Figure 11 This is the HAADF / ABF diagram after electrochemical induction in Example 4.

[0048] Figure 12 This is the HAADF / ABF diagram after electrochemical induction of Comparative Example 1.

[0049] Figure 13 This is the HAADF / ABF diagram after electrochemical induction of Comparative Example 2.

[0050] Figure 14 The materials of Examples 1-4 and Comparative Examples 1-2 are subjected to electrochemical induction on lithium half-cells at 0.2Ag. -1 Cycling performance under .

[0051] Figure 15 Specific capacity-voltage curves of the first discharge before electrochemical induction and the first charge before performance testing in Example 1.

[0052] Figure 16 This is the cycling performance of the sample in Example 1 for the full lithium iron phosphate battery at 0.2C. DETAILED DESCRIPTION

[0053] In order to better understand the technical content of the present invention, specific examples are provided below to further illustrate the present invention.

[0054] Unless otherwise specified, the experimental methods used in the examples of the present invention are all conventional methods.

[0055] Unless otherwise specified, the materials, reagents, etc. used in the examples of the present invention can be obtained from commercial sources.

[0056] Example 1

[0057] A method for preparing a carbon-interpenetrated ultrafine silicon network composite material comprises the following steps:

[0058] (1) Carbon skeleton pretreatment: the specific surface area is 18m 2 g -1 The carbon black aggregates were heat treated at 400℃ in air for 2 hours to oxidize and obtain carbon skeleton;

[0059] (2) Silicon composite: The carbon black aggregate was placed in a furnace, the silane concentration was controlled to 10% by volume, and the deposition time was 40 min to obtain a silicon particle composite with a silicon loading of 40 wt% and a particle size of 20-30 nm.

[0060] (3) Electrochemical induction: The battery was assembled with silicon particle composite as negative electrode, and the voltage range was 0.01-1.5V with 0.2Ag -1The current density was cycled three times to induce the formation of a carbon-interpenetrating ultrafine silicon network composite material.

[0061] Example 2

[0062] The difference from Example 1 is that the carbon black aggregates in step (2) are not placed in a furnace. Instead, the vapor-deposited silicon particles (40 wt%) and the carbon black aggregates (60 wt%) are mixed, high-energy ball milled at a speed of 400 rpm / min for 4 hours, dispersed in an aqueous solution with a solid content of 10%, and spray-dried. The remaining steps are the same as in Example 1.

[0063] Example 3

[0064] The difference from Example 1 is that the current density in step (3) is changed to 1.0Ag -1 , the remaining steps are the same as in Example 1.

[0065] Example 4

[0066] The difference from Example 1 is that the carbon black aggregate in step (1) is replaced with carbon fiber. The specific preparation steps are as follows:

[0067] Polyvinyl alcohol (PVA) was electrospun by electrospinning, and then sintered at 900 degrees in N2 for 2 hours to obtain fibers. The remaining steps were the same as in Example 1.

[0068] Comparative Example 1

[0069] The difference from Example 1 is that the carbon black aggregate in step (1) is replaced with multilayer graphene, and the remaining steps are the same as Example 1.

[0070] Comparative Example 2

[0071] The difference from Example 1 is that the carbon black aggregates in step (1) do not undergo a high-temperature oxidation treatment process, and the remaining steps are the same as Example 1.

[0072] The ultrafine structure characterization of the carbon interpenetrating ultrafine silicon network composite materials prepared in Examples 1-4 and Comparative Examples 1-2 is shown below:

[0073] Figure 1 From left to right are the SEM images of carbon black aggregates, carbon fibers, and multilayer graphene used in the examples of the present invention and the comparative examples, showing the morphology of the samples before the preparation process. And from Table 1, it can be seen that these carbon skeletons have a low specific surface area (<30m 2 g -1 ).

[0074] Table 1: Specific surface area of ​​different carbon materials

[0075]

[0076] Figure 2 These are silicon particles deposited by vapor phase reaction, and the particle size is 20-30nm. Figure 3 The following are brightfield (ABF) and darkfield (HAADF) transmission images of the deposition of nano-silicon on carbon black aggregates in Example 1. Because silicon has a higher atomic number than carbon in HAADF images, it has a higher Z contrast and appears brighter. Therefore, the HAADF / ABF comparison can be used to determine the location and state of silicon and carbon. Figure 3 It shows that the nano-silicon deposited on the carbon black aggregates is in a discrete state and is relatively evenly dispersed on the carbon black aggregates. Figure 4 The enlarged images of the three areas in the white dashed box in the ABF (the three on the far right) further show that the crystalline silicon is discretely distributed on the carbon black aggregates. Figure 5 The electrochemically induced lithiated silicon particles (Li x Si), these Li x Si aggregates together and sticks to each other, indicating the phenomenon of “lithiation fusion”. Figure 6 It shows the silicon particles in the delithiation state after electrochemical induction, and the silicon particles are partially connected to form a network structure. Figure 7 for Figure 6 The magnified atomic image between particles, the yellow dotted line is the junction of two particles, and the white dotted box is the magnified area ( Figure 7 The rightmost figure shows that silicon becomes amorphous after delithiation, and the particles are bonded with no obvious interfaces. Figure 8 This indicates that the ultrafine silicon network structure after electrochemical induction in Example 1 is interspersed with carbon, and the size of the silicon connecting branches is 4-50 nm. Figure 9 This shows that even if the vapor-deposited silicon particles and carbon black aggregates are uniformly mixed instead of being deposited directly, an ultrafine silicon network structure can be achieved after electrochemical induction. Example 3 uses a larger current of 1.0Ag -1 Electrochemical induction can also form an ultrafine silicon network structure ( Figure 10 In Example 4, the carbon black aggregates were replaced with carbon fibers, and an ultrafine silicon network structure was still generated after electrochemical induction ( Figure 11 However, in Comparative Example 1, where the carbon black aggregates are replaced with multilayer graphite sheets, no network structure can be generated, and the silicon particles aggregate together to form large particles ( Figure 12 ), it cannot inhibit silicon agglomeration like other carbon skeletons. This shows that whether or not an ultrafine silicon network can be formed is related to the structure of carbon. The more branched and dense the carbon structure, the easier it is to form an ultrafine silicon network structure with carbon interspersed. In addition, in Comparative Example 2, the carbon black aggregates were not oxidized, and the silicon particles also aggregated together ( Figure 13), indicating that the formation of an ultrafine silicon network is related to the carbon surface. The presence of numerous defects on the carbon surface allows silicon to adhere to the carbon and induce connections, making it easier to form an ultrafine silicon network structure interspersed with carbon.

[0077] The electrochemical performance of the carbon-interpenetrated ultrafine silicon network composite materials prepared in Examples 1-4 and Comparative Examples 1-2 was tested, and the results are shown below:

[0078] Figure 14 The performance of lithium half-cells of all examples and comparative examples is shown. It can be found that materials that can form a carbon-interpenetrated ultrafine silicon network structure after electrochemical induction can achieve good stability, while materials that cannot form this ultrafine network structure have a faster decay during the cycle. -1 The specific capacity reaches 1507mAhg -1 , the capacity retention rate after 100 cycles is 94.8%, and the performance of other materials with ultrafine network structure is similar to that of Example 1. Figure 15 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 77%. Considering the side reactions of the silicon negative electrode, the coulombic efficiency retention rate during this induction process is good. Figure 16 It shows that the full battery (N / P=1.2) of the material in Example 1 matched with the commercial LiFePO4 electrode sheet has a capacity of 137.9 mAh g after 50 cycles. -1 Decay to 135.3mAhg -1 , the capacity retention rate is as high as 98.1%.

[0079] Example 5

[0080] A method for preparing a carbon-interpenetrated ultrafine silicon network composite material comprises the following steps:

[0081] (1) Carbon skeleton pretreatment: the specific surface area is 18m 2 g -1 The carbon black aggregates were heat treated at 300℃ in air for 3 hours to oxidize and obtain carbon skeleton;

[0082] (2) Silicon composite: The carbon black aggregate was placed in a furnace, the silane concentration was controlled to be 12% by volume, and the deposition time was 45 min to obtain a silicon particle composite with a silicon loading of 45 wt% and a particle size of 20-30 nm;

[0083] (3) Electrochemical induction: The battery was assembled with silicon particle composite as negative electrode, and the voltage range was 0.01-1.5V with 0.2Ag -1 The current density was cycled 4 times to induce the formation of a carbon-interpenetrating ultrafine silicon network composite material.

[0084] Example 6

[0085] A method for preparing a carbon-interpenetrated ultrafine silicon network composite material comprises the following steps:

[0086] (1) Carbon skeleton pretreatment: the specific surface area is 18m 2 g -1 The carbon black aggregates were heat treated at 400℃ in air for 3 hours to oxidize and obtain carbon skeleton;

[0087] (2) Silicon composite: Silicon particles (45 wt%) and carbon black aggregates (55 wt%) were mixed, ball-milled at 300 rpm / min for 5 h, dispersed in aqueous solution with a solid content of 12 wt%, and spray-dried to obtain a silicon particle composite with a silicon loading of 45 wt% and a particle size of 20-30 nm.

[0088] (3) Electrochemical induction: The battery was assembled with silicon particle composite as negative electrode, and the voltage range was 0.01-1.5V with 0.2Ag -1 The current density was cycled 4 times to induce the formation of a carbon-interpenetrating ultrafine silicon network composite material.

[0089] 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 a carbon-interpenetrated ultrafine silicon network composite material, characterized in that: The following steps are involved: (1) Carbon skeleton pretreatment: the specific surface area is 18m 2 g -1 The carbon material is heat-treated in air at 300-400°C for 2-3 hours to oxidize the carbon skeleton; (2) Silicon composite: Silicon particles are loaded on the carbon skeleton to obtain a composite; (3) Electrochemical induction: Assemble the battery with the composite as the negative electrode and conduct the electrochemical induction with 0.2-1.0Ag in the voltage range of 0.01-1.5V. -1 The current density is cycled 3-4 times to induce the formation of a carbon-interpenetrating ultrafine silicon network composite material.

2. The method for preparing the carbon-interpenetrated ultrafine silicon network composite material according to claim 1, characterized in that: The carbon material is carbon black aggregate or carbon fiber.

3. The method for preparing the carbon-interpenetrated ultrafine silicon network composite material according to claim 1, characterized in that: Silicon particles are loaded on the carbon skeleton using a deposition method or a mixing method.

4. The method for preparing the carbon-interpenetrated ultrafine silicon network composite material according to claim 1, characterized in that: The particle size of the silicon particles is 20-30 nm; the loading amount of the silicon particles is 40 wt%-45 wt%.

5. The method for preparing the carbon-interpenetrated ultrafine silicon network composite material according to claim 3, characterized in that: When silicon particles are loaded on the carbon skeleton by vapor deposition, the silicon concentration volume fraction is controlled to be 10%-12%, and the deposition time is 40-45 minutes.

6. The method for preparing the carbon-interpenetrated ultrafine silicon network composite material according to claim 1, characterized in that: When silicon particles are loaded on the carbon skeleton by the mixing method, high-energy ball milling is performed at a rotation speed of 300-400 rpm for 4-5 hours, and the particles are dispersed in an aqueous solution with a solid content of 10-12 wt% and spray-dried.

7. The method for preparing the carbon-interpenetrated ultrafine silicon network composite material according to claim 1, characterized in that: The electrochemically induced current density was 0.2Ag -1 or 1.0Ag -1 .

8. The method for preparing the carbon-interpenetrated ultrafine silicon network composite material according to claim 1, characterized in that: The silicon network skeleton size of the carbon interpenetrating ultrafine silicon network composite material is 5-40 nm.

9. The carbon-interpenetrated ultrafine silicon network composite material obtained by the preparation method according to any one of claims 1 to 8, characterized in that: The structure includes: a continuous silicon network with carbon interpenetrating, silicon particles connected by non-interfacial bonding and a carbon interpenetrating ultrafine silicon network composite material with silicon connecting branches of 5-40nm in size.

10. Use of the carbon-intercalated ultrafine silicon network composite material obtained by the preparation method according to any one of claims 1 to 8 or the carbon-intercalated ultrafine silicon network composite material according to claim 9 in preparing negative electrode materials for lithium-ion batteries.

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