Nanometer confinement silicon-carbon negative electrode material and preparation method thereof

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a nanometer confinement silicon-carbon negative electrode material and a preparation method thereof.The preparation method comprises the following steps that S1, under the vacuum condition, bicarbonate powder is placed in a rapid Joule heat device to be subjected to heat treatment, and porous carbonate is obtained; s2, sieving the porous carbonate, and depositing nano silicon through chemical vapor deposition to obtain a carbonate / silicon composite material; s3, uniformly mixing the carbonate / silicon composite material with a reducing agent, placing the mixture in a rapid Joule heat device for an anhydrous and anaerobic reaction, and performing cooling, grinding, acid pickling, filtering, drying and screening on a reaction product to obtain primary silicon-carbon composite material powder; and S4, uniformly mixing the primary silicon-carbon composite material powder with asphalt, heating and curing under the protection of inert gas, and carbonizing to obtain the silicon-carbon negative electrode material. The preparation method is low in energy consumption, and the prepared silicon-carbon negative electrode material is good in coating effect and good in cycling stability.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a nano-confined silicon-carbon anode material and its preparation method. Background Technology

[0002] Developing next-generation high-performance energy storage systems is crucial for promoting the large-scale application of clean energy. With the continuous advancement of lithium-ion battery technology, the pursuit of anode materials with higher energy density and lower cost has become a research focus. Traditional graphite anodes, due to their limited theoretical capacity (372 mAh / g), are insufficient to meet the demands of future high-energy storage. Silicon-based materials, with their extremely high theoretical specific capacity (up to 4200 mAh / g) and low delithiation potential, are considered highly promising candidates for next-generation anodes. However, silicon exhibits significant volume expansion (>300%) during charge and discharge, leading to active material pulverization, continuous growth of the solid electrolyte interphase (SEI) film, and a sharp decline in cycle stability, severely restricting its practical application. Furthermore, the low first-cycle coulombic efficiency is also a major obstacle to the commercialization of silicon anodes. Constructing silicon-carbon composite materials, combining the structural buffering properties of the carbon matrix and the high-capacity characteristics of silicon, has become an effective strategy to mitigate volume changes and improve electrochemical performance. Therefore, developing novel silicon-carbon composite anodes with high initial efficiency, good structural stability, and low cost is not only crucial for improving the energy density of lithium-ion batteries, but also of significant research value for promoting the practical application of energy storage technologies.

[0003] To address the aforementioned issues, Chinese Patent CN109148883A discloses a method for preparing silicon / carbon nanocomposite materials through in-situ synthesis of metal hydrides and its application. Under a protective atmosphere, carbonate, nano-silica, ferrocene, and metal hydride are mixed and ball-milled at a mass ratio of 1:(2.5–20):(3–5):(3–30). Aluminum chloride is then added at a mass ratio of (5–15):1 to silica to obtain a precursor. The precursor is then calcined under a protective atmosphere, cooled, acid-washed, and dried to obtain the silicon / carbon nanocomposite material. This method is low-cost and produces a stable material structure. However, this patent uses a simple mechanical mixing method to mix nano-silica and the carbon precursor, resulting in uneven distribution of silicon and carbon layers after the reaction. Furthermore, silicon is easily exposed outside the carbon layer, leading to poor carbon coating. This problem not only reduces the initial coulombic efficiency of the silicon-carbon anode but also affects its cycle performance. In addition, the reaction system involves too many types of reactants, the reaction mechanism is complex, and the side reactions increase, which leads to an increase in by-products and affects the purity of the final product.

[0004] Therefore, how to provide a silicon-carbon material with low energy consumption, good coating effect, and excellent cycle performance is a key challenge currently facing our work. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that existing silicon-carbon materials have high energy consumption, poor coating effect and poor cycle stability. In order to overcome the above defects of the prior art, the present invention provides a nano-confined silicon-carbon anode material and its preparation method.

[0006] The technical solution of this invention is: a method for preparing a nano-confined silicon-carbon anode material, comprising the following steps: S1. Under vacuum conditions, bicarbonate powder is placed in a rapid Joule heating device for heat treatment to obtain porous carbonate. S2. The porous carbonate is sieved and then nano-silicon is deposited by chemical vapor deposition to obtain a carbonate / silicon composite material. S3. The carbonate / silicon composite material is mixed evenly with the reducing agent and placed in a rapid Joule heating device for anhydrous and oxygen-free reaction. The reaction product is cooled, ground, acid washed, filtered, dried and sieved to obtain primary silicon-carbon composite material powder. S4. The primary silicon-carbon composite material powder is mixed evenly with asphalt, and then heated, cured, and carbonized under inert gas protection to obtain silicon-carbon anode material.

[0007] This invention provides a preparation scheme based on a combination of porous carbonate templates and rapid Joule heating technology, culminating in a dense coating using pitch. Compared with traditional methods, this scheme offers the following significant advantages: a progressively designed process with outstanding structural advantages. First, rapid Joule heating decomposes bicarbonate, forming a porous carbonate template in situ. Then, nano-silicon is introduced via chemical vapor deposition, and Joule heating technology is used again to enable an ultrafast reaction between the carbonate and a reducing agent, constructing a three-dimensional conductive network framework of confined silicon particles in one step. Pitch is then introduced as a secondary carbon source, and through optimized low-temperature curing stabilization and high-temperature carbonization processes, a dense and complete amorphous carbon coating layer is formed on the surface of the primary composite material. This outer carbon shell works synergistically with the internal conductive network to minimize silicon volume expansion and reduce side reactions with the electrolyte. The resulting material significantly improves cycle stability (alleviating pulverization), rate performance (promoting ion / electron transport), and first-pass coulombic efficiency (up to 90%), providing a new research approach for the low-cost, large-scale manufacturing of high-performance silicon-carbon anodes. This preparation method uses a rapid Joule heating device, which has a short reaction time and low energy consumption. Conventional precursor carbon conversion requires long-term carbonization at high temperatures (600-1200℃) for 6-24 hours. This technology can complete the carbon conversion in just a few seconds.

[0008] In one possible implementation, the bicarbonate in step S1 is selected from at least one of sodium bicarbonate, potassium bicarbonate, magnesium bicarbonate, and calcium bicarbonate.

[0009] In one possible implementation, the parameters of the rapid Joule heating device in step S1 are: current 0-500A, output power 0-10000W, and time 0.01-3s. By rapidly decomposing bicarbonate through Joule heating, the ultra-fast reaction rate effectively avoids carbonate recrystallization and pore collapse caused by prolonged high temperatures in traditional heat treatment, thus successfully locking in the high-porosity structure formed by the escape of H2O and CO2. This structure provides a large specific surface area and abundant active sites for subsequent silicon deposition. More importantly, it provides a pre-designed and sufficient buffer space for the volume expansion of silicon during lithium intercalation.

[0010] In one possible implementation, the gas flow rate for chemical vapor deposition in step S2 is 5-100 sccm, the reaction time is 10-300 min, and the deposition temperature is 300-600℃. Using a porous carbonate framework as a template, uniform deposition of nano-silicon in three-dimensional space can be achieved through CVD. By adjusting the CVD parameters, the silicon loading and distribution can be precisely controlled, fundamentally avoiding the silicon agglomeration problem commonly found in physical mixing methods.

[0011] In one possible implementation, the mass ratio of the carbonate / silicon composite material to the reducing agent in step S3 is 10:1 to 1:10, and the reducing agent is selected from at least one of sodium hydride, lithium hydride, potassium hydride, lithium aluminum hydride, lithium borohydride, and sodium borohydride.

[0012] In one possible implementation, the parameters of the rapid Joule heating device in step S3 are: current of 200-3000A, output power of 5000-25000W, and reaction time of 0.1-3s. The extremely short reaction time of rapid Joule heating reduction (completing in seconds) avoids the silicon crystal size from increasing, keeping the silicon particles at a nanoscale and constructing a three-dimensional conductive network framework confined to the silicon particles. This significantly improves the overall electronic conductivity of the composite material, compensating for the poor conductivity of intrinsic silicon, thereby ensuring the material's rate performance at high current densities. The nano-silicon is confined within the carbon pores of the carbon framework, with buffer spaces reserved within the pores, and a silicon carbide bonding layer is generated in situ at the interface with the nano-silicon. This structure effectively alleviates the huge volume expansion of silicon (>300%) during lithiation, significantly enhancing the mechanical stability of the material and thus improving cycle life.

[0013] In one possible implementation, the pickling in step S3 is carried out by stirring with hydrochloric acid for 6-24 hours; the drying temperature is 80-120℃.

[0014] In one possible implementation, in step S4, the primary silicon-carbon composite powder is mixed with asphalt at a mass ratio of 1:(5% to 50%).

[0015] In one possible implementation, in step S4, curing is carried out at a constant temperature of 200-400℃ for 1-6 hours, and carbonization is carried out at a constant temperature of 700-1200℃ for 2-12 hours. A secondary asphalt coating process is introduced, forming a complete and dense amorphous carbon shell on the material surface through low-temperature stabilization and high-temperature carbonization. This carbon shell acts as a physical barrier, effectively isolating silicon from contact with the electrolyte, significantly suppressing side reactions and improving coulombic efficiency. Furthermore, it works in conjunction with the internal carbon skeleton to form a dual buffer mechanism of "skeleton support - outer constraint," further enhancing the adaptability to silicon volume expansion, thereby jointly ensuring the long-term structural stability and interface safety of the material.

[0016] Another aspect of the present invention is to provide a nano-confined silicon-carbon anode material, which is prepared by the above-described preparation method.

[0017] The beneficial effects of this invention are as follows: 1. Confined Construction and Interface Strengthening of Conductive Networks: Rapid Joule heating is used to perform second-level carbonization and reduction of the precursor, achieving one-step construction of a three-dimensional conductive carbon network, confinement of nano-silicon, and silicon carbide strengthening of the silicon / carbon interface. This process, while suppressing silicon particle growth, forms a synergistic structure of "conductive network-buffer space-silicon carbide interface layer," fundamentally solving the core problems of poor intrinsic conductivity and large volume expansion of silicon, directly ensuring the material's rate performance and mechanical stability.

[0018] 2. Secondary Dense Coating and Interface Stabilization: Based on the internal conductive framework, asphalt is introduced for secondary coating, forming a complete and dense amorphous carbon shell. This outer carbon shell and the inner carbon framework constitute a dual protection mechanism of "framework support - outer constraint," further suppressing electrolyte side reactions and synergistically buffering volume effects, which is key to improving the material's coulombic efficiency and long cycle life.

[0019] 3. One-step construction and structure locking of the porous framework: Rapid Joule heating was used to instantly decompose bicarbonate, utilizing its ultrafast heating characteristics to avoid recrystallization and pore collapse caused by traditional heat treatment. This successfully prepared and locked a high-porosity three-dimensional carbonate framework in situ. This structure not only provides a high specific surface area for subsequent silicon deposition but also pre-designs sufficient buffer space for the volume expansion of silicon, which forms the basis for all subsequent structural designs.

[0020] 4. Uniform and confined deposition of nano-silicon: Silicon deposition was carried out in a porous carbonate template prepared by an innovative method using CVD technology, which achieved uniform distribution and confinement of nano-silicon in three-dimensional space. This fundamentally avoids the problem of silicon agglomeration in physical mixing methods and lays the foundation for the formation of a uniform and stable composite structure.

[0021] 5. Mild and efficient precursor mixing: The vortex oscillation mixing method ensures that the reducing agent and porous precursor are mixed evenly, while effectively protecting their fragile microstructure from damage, thus providing a guarantee for achieving uniform and controllable subsequent reactions. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the silicon-carbon anode material of the present invention; Figure 2 This is a scanning electron microscope image of the primary silicon-carbon composite powder in Example 1; Figure 3 This is a scanning electron microscope image of the silicon-carbon anode material in Example 1; Figure 4 This is a transmission electron microscope (TEM) image of the silicon-carbon anode material in Example 1. Detailed Implementation

[0023] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter range described in the present invention. Reasonable variations derived therefrom are still within the protection scope of the claims of the present invention.

[0024] It should be noted that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0025] Unless otherwise defined, all terms, symbols, and other scientific terms used herein are intended to have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In some instances, terms having a conventional meaning are defined herein for clarification or ease of reference, and such definitions should not be construed as indicating a significant difference from conventional understanding in the art. The technical methods described or referenced herein are generally well understood by those skilled in the art and employed by conventional methods. Unless otherwise stated, the use of commercially available kits, reagents, and instruments shall be performed according to the manufacturer's instructions and parameters.

[0026] This invention provides a nano-confined silicon-carbon anode material and its preparation method. The method combines a porous carbonate template with rapid Joule heating technology, and ultimately achieves dense coating using pitch. Details are as follows: Step 1: Preparation of porous carbonates: Bicarbonates (such as sodium bicarbonate, potassium bicarbonate, magnesium bicarbonate, or calcium bicarbonate) are ground and sieved (using a 200-mesh sieve) into a uniform powder. The powder is then placed in a graphite crucible and subjected to rapid Joule heating in a vacuum environment. This rapid heating decomposes the bicarbonates into carbonates, and the released water and carbon dioxide molecules leave pores within the carbonates. The rapid heating prevents the disappearance of these pores caused by recrystallization of the produced carbonates. The settings for rapid Joule heating are: current 0-500A, output power 0-10000W, and time 0.1-3s.

[0027] Step 2: Chemical vapor deposition of nano-silicon: The obtained carbonate was sieved again (350 mesh screen) and then placed in a tube furnace. Nano-silicon was deposited on the surface and inside of the carbonate through a simple chemical vapor deposition (CVD) process to obtain a carbonate / silicon composite material. The gas flow rate in CVD was 5-100 sccm, the reaction time was 10min-300min, and the deposition temperature was 300-600℃.

[0028] Step 3: Fabrication of the three-dimensional conductive network framework of confined silicon particles: The deposited carbonate / silicon composite material was mixed with a reducing agent at a ratio of 10:1 to 1:10. The reducing agent included hydrides and aluminum hydrides: sodium hydride, lithium hydride, potassium hydride, lithium aluminum hydride; and borohydrides: lithium borohydride, sodium borohydride. The carbonate / silicon composite material and reducing agent were placed in centrifuge tubes and mixed using a vortex mixer. This mixing method does not damage the precursor structure, and the mixing time was 60-120 minutes. The mixed solid product was then subjected to a rapid Joule reaction in an anhydrous and oxygen-free environment (reaction current 200-3000A, output power 5000W-25000W, reaction time 0.1-5s). During the reaction, the carbonate particles carbonized in situ, forming a three-dimensional conductive network, and the silicon was bound in a nanoscale form, significantly improving the poor conductivity of silicon anode materials.

[0029] Step 4: Acid washing, purification, and drying: After the reaction is complete and the temperature is cooled, the product is ground and then acid-washed with hydrochloric acid at a concentration of 0.5-1.5 mol / L for 6-24 hours. It is then filtered and washed multiple times with deionized water until neutral. Finally, it is dried in an oven at 80-120℃ for 12-24 hours. After drying, the product is ground and sieved into uniform primary silicon-carbon composite powder.

[0030] Step 5: Asphalt Coating: The primary silicon-carbon composite material powder and asphalt powder with a softening point of 80℃~350℃ were mixed in a ball mill at a mass ratio of 1:(5%~50%). After uniform mixing under nitrogen protection, the mixture was transferred to a tube furnace. Under an inert atmosphere (such as nitrogen, flow rate 200 sccm), the temperature was first raised to 200℃~400℃ at a rate of 2℃ / min and held at a constant temperature for 1-6 hours for low-temperature stabilization treatment, allowing the asphalt to melt, crosslink, and uniformly wet the material surface. Subsequently, the temperature was further raised to 700℃~1200℃ at a rate of 5℃ / min and held at a constant temperature for 2-12 hours for high-temperature carbonization treatment, ultimately forming a dense amorphous carbon coating layer on the surface of the silicon-carbon composite material. After the reaction was completed, the product was cooled to room temperature in a nitrogen atmosphere with the furnace, and after slight grinding and sieving, the final silicon-carbon anode material was obtained.

[0031] The present invention will be further described below with reference to specific embodiments.

[0032] Example 1 Step 1: Place sodium bicarbonate powder (passed through a 200-mesh sieve) in a graphite crucible, and apply a 400A current (approximately 8000W power) for 0.5 seconds under vacuum to obtain a porous sodium carbonate template.

[0033] Step 2: After passing the template through a 350-mesh sieve, place it in a CVD tube furnace. Introduce silane carrier gas at a flow rate of 20 sccm and react at 450°C for 60 minutes.

[0034] Step 3: Vortex mix the deposited product with sodium borohydride (mass ratio 1:0.5) for 90 minutes. Then, perform rapid Joule thermal reduction in an anhydrous and oxygen-free environment with a current of 800A (power of approximately 12000W) for 1.0 second.

[0035] Step 4: The reduced product was acid-washed with 1.0 mol / L hydrochloric acid for 120 hours, followed by washing and drying to obtain the primary silicon-carbon composite material. The scanning electron microscope image of the primary silicon-carbon composite material obtained in this step is shown below. Figure 2 As shown, the three-dimensional network skeleton can be seen to be formed.

[0036] Step 5: The primary material and mesophase pitch (mass ratio 100:15) are mixed under nitrogen protection. Then, in a tube furnace, the mixture is first stabilized at 300℃ for 2 hours by increasing the temperature at 2℃ / min, and then carbonized at 1000℃ for 6 hours by increasing the temperature at 5℃ / min, yielding the final silicon-carbon anode material. The scanning electron microscope image of the obtained silicon-carbon anode material is shown below. Figure 3 As shown, the product particle size is excellent. Transmission electron microscopy analysis of one particle reveals... Figure 4As shown in the TEM image, silicon particles are deposited on an amorphous carbon framework, with a SiC layer surrounding the silicon particles, and a carbon layer surrounding the amorphous carbon. A schematic diagram of this nano-confined silicon-carbon anode material can be found in [reference needed]. Figure 1 As shown.

[0037] The nano-confined silicon-carbon anode material has a silicon content of 28 wt.%, an initial charge capacity of 1350 mAh / g, an initial coulombic efficiency of 90.0%, a capacity retention of 89% after 100 cycles at a 1C current density, and a volume expansion rate of 26%.

[0038] Example 2 The difference between this embodiment and Embodiment 1 is that in step two, the CVD deposition silane flow rate is 40 sccm, the time is 120 min, and the temperature is 500℃. In step five, the mass ratio of asphalt to primary silicon-carbon composite material is 100:20.

[0039] The obtained nano-confined silicon-carbon anode material has a silicon content of 35 wt.%, an initial charge capacity of 1580 mAh / g, an initial coulombic efficiency of 87.5%, a capacity retention rate of 86% after 100 cycles at a current density of 1C, and a volume expansion rate of 33%.

[0040] Example 3 The difference between this embodiment and Embodiment 1 is that in step two, the CVD deposition of silane is performed at a flow rate of 15 sccm for 90 min at a temperature of 400℃. In step three, the reducing agent is lithium aluminum hydride (the mass ratio of the deposited product to the reducing agent is 1:0.6), and the rapid Joule thermal reaction time is 0.8 seconds.

[0041] The obtained nano-confined silicon-carbon anode material has a silicon content of 22 wt.%, an initial charge capacity of 1180 mAh / g, an initial coulombic efficiency of 91.5%, a capacity retention of 93% after 100 cycles at a current density of 1C, and a volume expansion rate of 20%.

[0042] Example 4 The difference between this embodiment and Embodiment 2 is that: in step 3, the reducing agent is lithium aluminum hydride (the mass ratio of the deposited product to the reducing agent is 1:0.6), the current of the second Joule thermal reaction is 1200A (power is about 18000W), and the time is 1.5 seconds.

[0043] The obtained nano-confined silicon-carbon anode material has a silicon content of 35 wt.%, an initial charge capacity of 1580 mAh / g, an initial coulombic efficiency of 89.0%, a capacity retention rate of 88% after 100 cycles at a current density of 1C, and a volume expansion rate of 30%.

[0044] Example 5 The difference between this embodiment and Embodiment 2 is that in step five, the mass ratio of asphalt to primary silicon-carbon composite material is 100:25, and the carbonization temperature is increased to 1100℃. In step three, the rapid Joule heating reaction time is 1.0 second.

[0045] The obtained nano-confined silicon-carbon anode material has a silicon content of 32 wt.%, an initial charge capacity of 1490 mAh / g, an initial coulombic efficiency of 90.5%, a capacity retention rate of 91% after 100 cycles at a current density of 1C, and a volume expansion rate of 23%.

[0046] Example 6 The difference between this embodiment and Embodiment 1 is as follows: Step 1, the Joule heat treatment current is 500A (power approximately 10000W), and the time is 0.8 seconds. Step 2 is the same as in Embodiment 2. Step 3 is the same as in Embodiment 4, but the reaction time is 1.8 seconds. Step 5 is the same as in Embodiment 5.

[0047] The obtained nano-confined silicon-carbon anode material has a silicon content of 38 wt.%, an initial charge capacity of 1680 mAh / g, an initial coulombic efficiency of 87.0%, a capacity retention of 87% after 100 cycles at a current density of 1C, and a volume expansion rate of 32%.

[0048] Example 7 The difference between this embodiment and Embodiment 2 is that the CVD deposition time in step two is extended to 180 min, and the temperature is adjusted to 480℃. Step three is the same as in Embodiment 4, with a reaction time of 2.0 seconds. In step five, the carbonization condition is a constant temperature of 900℃ for 8 hours.

[0049] The obtained nano-confined silicon-carbon anode material has a silicon content of 41 wt.%, an initial charge capacity of 1750 mAh / g, an initial coulombic efficiency of 85.5%, a capacity retention of 84% after 100 cycles at a current density of 1C, and a volume expansion rate of 36%.

[0050] Example 8 The difference between this embodiment and Embodiment 3 is that the concentration of hydrochloric acid used for pickling in step four is 0.8 mol / L, and the pickling time is 100 hours. Step five is the same as in Embodiment 5. The reaction time in step three is 0.8 seconds.

[0051] The obtained nano-confined silicon-carbon anode material has a silicon content of 22 wt.%, an initial charge capacity of 1180 mAh / g, an initial coulombic efficiency of 92.0%, a capacity retention of 94% after 100 cycles at a current density of 1C, and a volume expansion rate of 19%.

[0052] Example 9 The difference between this embodiment and Embodiment 6 is that the mass ratio of asphalt to primary material in step five is 100:30. The reaction time in step three is 1.0 second.

[0053] The obtained nano-confined silicon-carbon anode material has a silicon content of 31 wt.%, an initial charge capacity of 1450 mAh / g, an initial coulombic efficiency of 91.5%, a capacity retention of 95% after 100 cycles at a 1C current density, and a volume expansion rate of 18%.

[0054] Example 10 The difference between this embodiment and Embodiment 2 is that in step two, the CVD deposition silane flow rate is 35 sccm and the time is 100 min. Step three is the same as in Embodiment 4, but the reaction time is 1.5 seconds. Step five is the same as in Embodiment 9.

[0055] The obtained nano-confined silicon-carbon anode material has a silicon content of 33 wt.%, an initial charge capacity of 1520 mAh / g, an initial coulombic efficiency of 91.0%, a capacity retention of 93% after 100 cycles at a current density of 1C, and a volume expansion rate of 21%.

[0056] Example 11 The difference between this embodiment and Embodiment 1 is as follows: In Step 1, the Joule heating current is 350A (approximately 7000W), and the time is 0.3 seconds. In Step 2, the silane flow rate is 25 sccm, the temperature is 430℃, and the time is 150 min. In Step 3, sodium borohydride is used, with a current of 1000A (approximately 15000W) and a time of 1.2 seconds. In Step 5, the mass ratio of asphalt to primary materials is 100:22, and the carbonization condition is a constant temperature of 950℃ for 7 hours.

[0057] The obtained nano-confined silicon-carbon anode material has a silicon content of 29 wt.%, an initial charge capacity of 1380 mAh / g, an initial coulombic efficiency of 90.5%, a capacity retention of 92% after 100 cycles at a current density of 1C, and a volume expansion rate of 24%.

[0058] Example 12 The difference between this embodiment and embodiment 7 is that step five is the same as in embodiment 5. The reaction time in step three is 2.0 seconds.

[0059] The obtained nano-confined silicon-carbon anode material has a silicon content of 39 wt.%, an initial charge capacity of 1700 mAh / g, an initial coulombic efficiency of 86.5%, a capacity retention of 86% after 100 cycles at a 1C current density, and a volume expansion rate of 34%.

[0060] Example 13 The difference between this embodiment and Example 1 is as follows: Step 1 uses the conditions of Example 6 (current 500A, time 0.8s). Step 2 uses the conditions of Example 2 (flow rate 40sccm, 120min, 500℃). Step 3 uses the conditions of Example 4 (reducing agent lithium aluminum hydride, current 1200A, time 1.5s). Step 4 uses the conditions of Example 8 (hydrochloric acid 0.8mol / L, pickling for 100h). Step 5 uses the conditions of Example 9 (asphalt ratio 100:30).

[0061] The obtained nano-confined silicon-carbon anode material has a silicon content of 35 wt.%, an initial charge capacity of 1580 mAh / g, an initial coulombic efficiency of 90.0%, a capacity retention of 96% after 100 cycles at a current density of 1C, and a volume expansion rate of 16%.

[0062] Comparative Example 1 This comparative example is a test to compare insufficient silicon deposition based on Example 1. The difference from Example 1 is that the CVD deposition conditions in step two were extremely mild, with a silane flow rate of 5 sccm, a time of 30 min, and a temperature of 350°C, resulting in severely insufficient silicon deposition. The rapid Joule heating reaction time in step three was 0.5 seconds.

[0063] The obtained silicon-carbon anode material has a silicon content of 8 wt.%, an initial charge capacity of 650 mAh / g, an initial coulombic efficiency of 85.5%, a capacity retention of 95% after 100 cycles at a 1C current density, and a volume expansion rate of 15%. Due to the low silicon content, the material capacity is significantly lower than that of all other embodiments, failing to fully utilize the high capacity advantage of silicon-carbon composite materials.

[0064] Comparative Example 2 This comparative example is a comparative experiment conducted based on Example 2, demonstrating the formation of dense carbon without a gas template effect. The difference from Example 2 is that in step three, magnesium powder (Mg) was used as the reducing agent (the mass ratio of carbonate / silicon to magnesium powder was 1:0.7), the rapid Joule heating current was 500A (approximately 10000W), and the reaction time was 1.0 second. This reaction is a solid-phase reduction, producing no gaseous products and failing to form a porous carbon framework; the final result is a mixture of silicon particles and dense carbon.

[0065] The obtained silicon-carbon anode material has a silicon content of 35 wt.%, an initial charge capacity of 1500 mAh / g, an initial coulombic efficiency of 68.0%, a capacity retention of 45% after 100 cycles at a 1C current density, and a volume expansion rate of 68%. Due to the lack of a porous conductive network, the material has extremely low initial efficiency and very poor cycle performance and structural stability.

[0066] Comparative Example 3 The difference between this comparative example and Example 2 is that the asphalt coating amount in step five is extremely low, the mass ratio of asphalt to primary material is 100:3, and the carbonization conditions are insufficient (700℃, 2 hours), resulting in an incomplete carbon coating layer.

[0067] The obtained silicon-carbon anode material has a silicon content of 44 wt.%, an initial charge capacity of 1750 mAh / g, an initial coulombic efficiency of 78.0%, a capacity retention of 45% after 100 cycles at a 1C current density, and a volume expansion rate of 65%. Due to insufficient carbon coating, the volume expansion of silicon particles cannot be effectively limited, and the material's cycle performance deteriorates sharply.

[0068] The performance test results of the silicon-carbon anode materials for lithium-ion batteries obtained in each embodiment and comparative example are shown in Table 1 below.

[0069] Table 1 Performance test results of silicon-carbon anode materials for lithium-ion batteries obtained in each embodiment and comparative example Based on Table 1, the following conclusions can be drawn: First, the preparation of the porous carbonate template and the chemical vapor deposition (CVD) process jointly determine the loading and distribution of active silicon. By adjusting the CVD process parameters, the silicon content in the final composite material can be effectively controlled. Specifically, when the silane carrier gas flow rate is increased from 20 sccm to 40 sccm, the deposition time from 60 minutes to 120 minutes, and the deposition temperature from 450°C to 500°C (see the comparison between Examples 1 and 2), the silicon content increases from 28 wt.% to 35 wt%, and its initial charge capacity correspondingly increases significantly from 1350 mAh / g to 1580 mAh / g. However, excessive silicon deposition leads to deterioration of electrochemical performance. As shown in Example 7, when the silicon content reaches 41 wt.%, the drastic volume expansion effect causes a decrease in the material's structural stability, manifested in a reduction in capacity retention after 100 cycles to 84% and an increase in volume expansion rate to 36%. This indicates that in the system of this invention, there exists a silicon loading window that achieves an optimal balance between capacity characteristics and cycle stability.

[0070] Secondly, the process parameters of the second rapid Joule thermal reduction process are crucial for constructing a high-quality three-dimensional conductive carbon network. Using a strong reducing agent and optimized reaction energy can significantly improve the electrochemical interface stability of the material. Comparing Examples 2 and 4, it can be seen that under the same silicon content (35 wt.%), using lithium aluminum hydride as the reducing agent and increasing the reaction current to 1200 A and the reaction time to 1.5 seconds (Example 4) allows for a more complete reduction reaction, forming a more robust conductive framework. This results in an increase in the initial coulombic efficiency from 87.5% to 89.0% and the capacity retention after 100 cycles from 86% to 88%. These results indicate that optimized reduction conditions help enhance the conductivity of the carbon network and effectively buffer the volume changes of silicon during cycling.

[0071] Third, post-treatment with asphalt coating is a key step in significantly improving the interfacial stability and cycle life of the material. Appropriately increasing the asphalt coating amount and optimizing the carbonization process can effectively enhance the overall electrochemical performance of the material. As shown in the comparison of Examples 2, 9, and 13, with similar silicon content (31-35 wt.%), increasing the asphalt coating ratio from 20% to 30% significantly increases the initial coulombic efficiency from 87.5% to 91.5%, the capacity retention after 100 cycles from 86% to 95%-96%, and the volume expansion rate from 33% to 16%-18%. This is mainly attributed to the fact that a thicker, more complete carbon coating layer can effectively suppress the volume expansion of silicon particles and significantly reduce side reactions between the electrode material and the electrolyte.

[0072] Of particular note is Example 13, as a comprehensive optimization example. By integrating the optimal conditions of each process step (Step 1: 500A current treatment for 0.8 seconds; Step 2: 40 sccm silane flow rate, deposition at 500°C for 120 minutes; Step 3: lithium aluminum hydride reducing agent, treatment at 1200A current for 1.5 seconds; Step 5: 30% bitumen coating), it successfully achieved optimal cycling performance (96% capacity retention after 100 cycles) and the lowest volume expansion rate (16%) while maintaining high reversible capacity (1580 mAh / g) and high initial coulombic efficiency (90.0%). This result fully demonstrates the importance and effectiveness of the synergistic optimization of process parameters described in this invention.

[0073] In summary, this invention successfully constructed a composite anode material with a multi-level synergistic structure of "high-capacity uniform silicon loading - robust three-dimensional conductive network - dense carbon coating layer" by precisely controlling the process parameters of each key step in porous template preparation, chemical vapor deposition of silicon, rapid Joule thermal reduction, and pitch coating. This material system cleverly balances high specific capacity, high initial coulombic efficiency, and excellent long cycle life, effectively solving the core technical challenges faced by silicon-carbon anode materials in commercial applications. Furthermore, the preparation process involved in this invention is characterized by high efficiency, speed, and low energy consumption, demonstrating significant technical advantages and broad prospects for industrial application.

[0074] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing a nano-confined silicon-carbon anode material, characterized in that, Includes the following steps: S1. Under vacuum conditions, bicarbonate powder is placed in a rapid Joule heating device for heat treatment to obtain porous carbonate. S2. The porous carbonate is sieved and then nano-silicon is deposited by chemical vapor deposition to obtain a carbonate / silicon composite material. S3. The carbonate / silicon composite material is mixed evenly with the reducing agent and placed in a rapid Joule heating device for anhydrous and oxygen-free reaction. The reaction product is cooled, ground, acid washed, filtered, dried and sieved to obtain primary silicon-carbon composite material powder. S4. The primary silicon-carbon composite material powder is mixed evenly with asphalt, and then heated, cured, and carbonized under inert gas protection to obtain silicon-carbon anode material.

2. The preparation method according to claim 1, characterized in that, In step S1, the bicarbonate is selected from at least one of sodium bicarbonate, potassium bicarbonate, magnesium bicarbonate, and calcium bicarbonate.

3. The preparation method according to claim 1, characterized in that, The parameters for the rapid Joule heating device in step S1 are: current 0-500A, output power 0-10000W, and time 0.01-3s.

4. The preparation method according to claim 1, characterized in that, In step S2, the gas flow rate for chemical vapor deposition is 5-100 sccm, the reaction time is 10-300 min, and the deposition temperature is 300-600℃.

5. The preparation method according to claim 1, characterized in that, In step S3, the mass ratio of carbonate / silicon composite material to reducing agent is 10:1 to 1:10, and the reducing agent is selected from at least one of sodium hydride, lithium hydride, potassium hydride, lithium aluminum hydride, lithium borohydride, and sodium borohydride.

6. The preparation method according to claim 1, characterized in that, The parameters for the rapid Joule heating device in step S3 are: current of 200-3000A, output power of 5000-25000W, and reaction time of 0.1-3s.

7. The preparation method according to claim 1, characterized in that, In step S3, pickling is performed using hydrochloric acid with stirring for 6-24 hours; the drying temperature is 80-120℃.

8. The preparation method according to claim 1, characterized in that, In step S4, the primary silicon-carbon composite powder and asphalt are mixed at a mass ratio of 1:(5% to 50%).

9. The preparation method according to claim 1, characterized in that, In step S4, curing is carried out at a constant temperature of 200-400℃ for 1-6 hours, and carbonization is carried out at a constant temperature of 700-1200℃ for 2-12 hours.

10. A nano-confined silicon-carbon anode material, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

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