A hydrothermal construction porous carbon composite framework suitable for a CVD silicon carbon negative electrode, a silicon carbon negative electrode material and a preparation method thereof

Abstract

The application discloses a kind of suitable for CVD silicon-carbon negative electrode hydrothermal construction porous carbon composite framework material and preparation method and application, belong to lithium ion battery negative material technical field.The method includes: (1) melamine, resorcinol, formaldehyde and surfactant are dispersed in solvent, carbon nanotube and graphene dispersion liquid are added, and stirring is formed uniform precursor mixed solution;(2) hydrothermal reaction is carried out at 120~200 ℃ for 6~24h, and resin is in-situ polymerized on the surface of carbon nanotube / graphene;(3) after carbonization, activation, three-dimensional interconnected conductive hierarchical porous carbon framework is obtained;(4) porous carbon framework is placed in CVD equipment, and silane gas is introduced at 400~600 ℃ for 1~8h, and silicon-carbon negative electrode material is obtained.The application constructs carbon nanotube / graphene enhanced three-dimensional conductive framework by hydrothermal in-situ polymerization, and combined with hierarchical pore structure design, can significantly improve silicon deposition uniformity, buffer silicon volume expansion and enhance structural stability, and the obtained silicon-carbon negative electrode material is excellent in cycle stability, rate performance and first coulomb efficiency, suitable for batch preparation, with good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode material technology, specifically relating to a hydrothermal porous carbon composite framework material for chemical vapor deposition (CVD) silicon-carbon anodes, its preparation method and application, and particularly to a multi-level porous silicon deposition carrier material formed by hydrothermal polymerization, carbonization and activation of a resin polymerization system as the main body and carbon nanotubes / graphene as the conductive framework, and its application in high-performance silicon-carbon anodes. Background Technology

[0002] With the rapid development of high-energy-density lithium-ion batteries, the theoretical specific capacity of traditional graphite anodes is relatively low (372 mAh·g). -1 The current technology is insufficient to meet the urgent needs of new energy vehicles and large-scale energy storage for high-energy-density, long-life batteries. Silicon materials, due to their high specific energy (approximately 4200 mAh·g), are more suitable. -1 Theoretical specific capacity, lower lithium intercalation potential (0.4 V vs. Li / Li) + And with its abundant reserves in the Earth's crust, it is widely recognized as one of the most promising next-generation lithium-ion battery anode materials.

[0003] However, silicon undergoes a massive volume expansion exceeding 300% during charge and discharge, which can easily lead to the pulverization of active particles, damage to the electrode structure, and continuous rupture and reconstruction of the solid electrolyte interphase (SEI) film, resulting in rapid capacity decay and a sharp decline in cycle stability. Therefore, current research on silicon-carbon anodes focuses on mitigating the volume effect of silicon by constructing a reasonable silicon / carbon composite structure, while simultaneously improving the electronic conductivity of the material.

[0004] Existing commercial and research silicon-carbon anode materials mostly use ordinary activated carbon, hard carbon, or simple template carbon as silicon deposition supports, but they generally suffer from the following technical bottlenecks: a single pore structure, mainly micropores, making it difficult to simultaneously achieve high silicon loading and sufficient volume expansion buffer space; discontinuous conductive networks, resulting in long electron transport paths and high impedance, leading to limited rate performance; insufficient mechanical strength of the carbon skeleton, making it prone to structural collapse during cycling, causing active material detachment; poor silicon deposition uniformity, with silane gas readily nucleating on the material surface, forming large particle agglomerates; and a lack of effective active sites on the carbon material surface, resulting in weak bonding between CVD-deposited silicon and the carbon skeleton, making it prone to peeling during cycling.

[0005] In addition, some existing porous carbon preparation methods introduce conductive components such as carbon nanotubes or graphene through simple physical mixing, which makes it difficult to achieve a three-dimensional integrated growth structure. The conductive components are prone to self-aggregation, which cannot give full play to their synergistic enhancement effect and limits the further improvement of the material's overall electrochemical performance.

[0006] Therefore, developing a silicon deposition carrier material that combines high specific surface area, hierarchical porous structure, continuous three-dimensional conductive network, and excellent structural stability is of great significance for breaking through the performance bottleneck of existing CVD silicon-carbon anodes and promoting their industrial application. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention proposes a hydrothermal porous carbon composite framework material suitable for CVD silicon-carbon anodes and its preparation method. This invention induces the uniform coating of a resin precursor onto the surface of carbon nanotubes / graphene through hydrothermal in-situ polymerization. Subsequent carbonization and activation processes construct a three-dimensional interconnected hierarchical porous carbon framework, which is then used for CVD deposition of nano-silicon. This effectively improves the uniformity of silicon dispersion, enhances the material's conductivity, and buffers the volume expansion of silicon.

[0008] Compared with existing technologies, the porous carbon framework constructed by this invention has higher structural stability and conductivity continuity, and also possesses a multi-level porous structure with micropore-mesopore synergy, which can significantly improve the cycle stability, rate performance and first coulombic efficiency of silicon-carbon anodes.

[0009] It should be understood that the foregoing general description and the following detailed description are merely illustrative and not intended to limit the invention. This invention document provides an overview of various implementations or examples of the techniques described herein, and is not a complete disclosure of the full scope or all features of the disclosed techniques. Various embodiments are given generally by way of example rather than limitation, and are used together with the specification and claims to illustrate the disclosed embodiments.

[0010] According to one aspect of the present invention, an object of the present invention is to provide a hydrothermal porous carbon composite framework material suitable for CVD silicon-carbon anodes, characterized in that: the porous carbon composite framework material is mainly composed of carbonized resin-derived carbon, with carbon nanotubes and graphene uniformly dispersed inside; the resin-derived carbon, carbon nanotubes and graphene together construct a three-dimensional interconnected conductive hierarchical porous network; and nano-silicon particles are uniformly deposited on the surface of the material and inside the pores.

[0011] Preferably, the porous carbon composite framework material has a specific surface area of ​​800~2000 m² / g and a total pore volume of 0.8~2.5 cm³ / g; wherein the volume of mesopores (2~50 nm) accounts for 40%~70% of the total pore volume.

[0012] Preferably, the mass ratio of carbon nanotubes to graphene is 1:5 to 5:1, and the total mass of the two accounts for 1% to 15% of the total mass of the porous carbon composite framework material.

[0013] In this case, the mass of the nano-silicon particles accounts for 20% to 60% of the total mass of the final silicon-carbon composite anode material, and the average particle size of the silicon particles is 5 to 50 nm.

[0014] According to another aspect of the present invention, another object of the present invention is to provide a method for preparing the above-mentioned porous carbon composite framework material, comprising the following steps: Melamine, surfactant, formaldehyde, and deionized water are mixed to form solution A; resorcinol, formaldehyde, and ethanol are mixed to form solution B; carbon nanotubes and graphene are dispersed to form solution C; solutions A, B, and C are mixed and stirred to form a homogeneous precursor mixture. The precursor mixture was placed in a closed reactor and subjected to a hydrothermal reaction at 120-200°C for 6-24 h to induce in-situ sol-gel polymerization of the resin on the surface of carbon nanotubes / graphene. After washing and drying, the hydrothermal products are carbonized at 700~1000℃ for 2~6 h under an inert atmosphere; The carbonization product was mixed with an activator and activated at 700-900℃ for 1-4 h. After washing and drying, a porous carbon composite framework was obtained. The skeleton is placed in a CVD apparatus, silane gas is introduced, and deposition is carried out at 400~600℃ for 1~8 h to obtain silicon-carbon anode material.

[0015] In step (1), the surfactant includes F127; the solvent includes a mixture of deionized water and ethanol.

[0016] In step (2), the hydrothermal reaction temperature is preferably 150~190℃ and the reaction time is preferably 8~16h.

[0017] In step (3), the inert atmosphere is argon or nitrogen; the carbonization heating rate is 1~10℃·min⁻¹.

[0018] In step (4), the activator includes one or more of KOH, NaOH, ZnCl2, water vapor or CO2; the mass ratio of the activator to the carbon material is 1:1 to 5:1.

[0019] In step (5), the silicon source includes one of silane, silane or dichlorosilane; an inert gas is used as the carrier gas during the deposition process.

[0020] Compared with the prior art, the present invention has the following significant advantages: Constructing a continuous three-dimensional conductive network: The interweaving of carbon nanotubes and graphene forms interconnected conductive pathways, effectively reducing electron transport impedance and significantly improving the rate performance of the material. Improving silicon deposition uniformity: The resin-coated structure formed through hydrothermal in-situ polymerization provides abundant nucleation sites, ensuring uniform distribution of CVD silicon on the inner walls of the pores and the surface of the framework, avoiding local agglomeration. Efficiently buffering silicon volume expansion: The hierarchical porous structure with micropore-mesopore synergy provides ample buffer space for silicon lithium intercalation expansion, reducing structural stress during cycling. Enhancing framework structural stability: Carbon nanotubes / graphene, as reinforcing phases embedded in the resin-derived carbon matrix, significantly improve the mechanical strength of the carbon framework and suppress structural collapse during cycling. Optimizing SEI film formation: Defects and oxygen-containing functional groups on the porous carbon surface facilitate the formation of a uniform and stable SEI film, reducing electrolyte side reactions and improving cycling stability and first coulombic efficiency. Combining high capacity and long cycling performance: This structural design can simultaneously improve silicon utilization and cycling stability, achieving a synergistic improvement in high specific capacity and long lifetime, making it suitable for industrial-scale mass production.

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 The image shows a scanning electron microscope (SEM) image of the porous carbon material obtained in Example 1.

[0023] Figure 2 The image shows the Raman spectrum of the silicon-carbon composite material obtained in Example 1.

[0024] Figure 3 The graph shows the cycle performance of the silicon-carbon anode obtained in Example 1. Detailed Implementation Plan

[0025] The present invention will now be described in detail. Before proceeding with the description, it should be understood that the terminology used in this specification and the appended claims should not be construed as limited to its general or dictionary meaning, but rather should be interpreted according to the meaning and concept corresponding to the technical aspects of the invention, based on the principle that the inventors are allowed to appropriately define the terms for the best interpretation. Therefore, the description presented herein is merely a preferred example for illustrative purposes and is not intended to limit the scope of the invention. It should be understood that other equivalents or modifications can be obtained from it without departing from the spirit and scope of the invention.

[0026] In this document, the terms “comprising,” “including,” “having,” “containing,” or any other similar terms are open-ended conjunctions intended to cover non-exclusive inclusions. For example, a composition or article containing a plurality of elements is not limited to those listed herein, but may also include other elements not explicitly listed but typically inherent to the composition or article. Furthermore, unless explicitly stated to the contrary, the term “or” is inclusive, not exclusive. For example, the condition “A or B” is satisfied in any of the following cases: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); A and B are both true (or exist). Moreover, in this document, the terms “comprising,” “including,” “having,” and “containing” should be interpreted as specifically disclosed and simultaneously cover closed or semi-closed conjunctions such as “composed of” and “substantially composed of.”

[0027] In this document, all features or conditions defined in the form of numerical ranges or percentage ranges are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible secondary ranges and individual values ​​within those ranges, particularly integer values. For example, a range description of "1 to 8" should be considered as specifically disclosing all secondary ranges such as 1 to 7, 2 to 8, 2 to 6, 3 to 6, 4 to 8, 3 to 8, etc., particularly secondary ranges defined by all integer values, and should be considered as specifically disclosing individual values ​​within those ranges such as 1, 2, 3, 4, 5, 6, 7, 8, etc. Unless otherwise specified, the foregoing interpretation applies to all content throughout this invention, regardless of its scope.

[0028] If a quantity or other numerical value or parameter is expressed as a range, a preferred range, or a series of upper and lower limits, it should be understood that this document has specifically disclosed all ranges consisting of any upper or preferred value of that range and the lower or preferred value of that range, regardless of whether such ranges are separately disclosed. Furthermore, when a range of numerical values ​​is mentioned herein, unless otherwise stated, the range shall include its endpoints and all integers and fractions within the range.

[0029] In this document, numerical values ​​are to be understood as having a precision with significant digits, provided that the purpose of the invention can be achieved. For example, the number 40.0 should be understood to cover the range from 39.50 to 40.49.

[0030] The following embodiments are merely examples illustrating implementations of the present invention and do not constitute any limitation on the present invention. Those skilled in the art will understand that modifications made without departing from the spirit and concept of the present invention fall within the protection scope of the present invention. Unless otherwise specified, the reagents and instruments used in the following embodiments are commercially available products.

[0031] Example 1: Precursor Preparation. 1.6 g of melamine, 0.4 g of F127, and 2.7 g of formaldehyde were added to 20 mL of deionized water and stirred at 70°C for 1 h to obtain a homogeneous and transparent solution A. 2.6 g of resorcinol and 4.6 g of formaldehyde were added to 20 mL of ethanol and mixed thoroughly to form solution B. A carbon nanotube / graphene composite slurry (carbon nanotube to graphene mass ratio 1:1, total mass 0.2 g) was ultrasonically dispersed for 30 min to obtain solution C. Solutions A, B, and C were mixed and stirred continuously for 30 min to form a homogeneous polymerization precursor mixture.

[0032] The resulting mixture was transferred to a 100 mL stainless steel reactor lined with polytetrafluoroethylene, sealed, and placed in an oven for hydrothermal reaction at 180°C for 12 h, followed by natural cooling to room temperature.

[0033] Carbonization and activation: The hydrothermal product was washed three times alternately with deionized water and ethanol, and then vacuum-dried at 60℃ for 12 h. The dried product was then placed in a tube furnace and carbonized at 800℃ under an argon atmosphere at a heating rate of 5℃·min⁻¹ for 2 h. After cooling to room temperature, the carbonized product was uniformly mixed with KOH activator at a mass ratio of 1:3, and then placed back in a tube furnace and activated at 800℃ under an argon atmosphere at a heating rate of 5℃·min⁻¹ for 1 h. The activated product was washed with 1 mol / L hydrochloric acid solution until neutral, then washed with deionized water until the pH of the filtrate was 7, and finally vacuum-dried at 80℃ for 12 h to obtain a porous carbon composite framework material.

[0034] Silicon deposition by CVD: The obtained porous carbon framework material is placed in a fluidized bed CVD device, purged with nitrogen for 30 min, heated to 500℃ at a heating rate of 5℃·min⁻¹, and deposited with silane gas (volume fraction 10%, nitrogen as carrier gas) for 4 h. Then, nitrogen is introduced to cool down to room temperature to obtain silicon-carbon composite anode material.

[0035] Comparative Example 1 (hydrothermal in-situ polymerization) used the same precursors and proportions as Example 1. The difference was that the hydrothermal reaction step was skipped, and the mixture was directly stirred in a 60°C water bath, followed by carbonization, activation, and CVD silicon deposition under the same conditions as in Example 1.

[0036] The results show that, due to the lack of a three-dimensional cross-linked network formed under hydrothermal conditions, significant phase separation occurs between the resin and the conductive agent, resulting in a loose carbon framework structure and a discontinuous conductive network. After CVD deposition, silicon exhibits significant agglomeration on the material surface, failing to achieve uniform distribution. Cyclic testing results show that the capacity and retention rate of this comparative sample are significantly lower than those of Example 1 after 50 cycles, demonstrating poor structural stability.

[0037] Comparative Example 2 (without CNT / graphene conductive framework): In the precursor preparation stage, no carbon nanotubes and graphene were added. Only resorcinol, melamine and formaldehyde were used for hydrothermal polymerization, carbonization, activation and CVD deposition. The remaining process parameters were exactly the same as those in Example 1.

[0038] The results show that, due to the lack of a continuous conductive framework, the obtained material exhibits a typical amorphous carbon structure with weak electron transport capability. Under high-rate charge-discharge conditions, electrode polarization is significantly enhanced, and the rate performance is significantly worse than that of Example 1; at the same time, the electrode impedance increases rapidly during cycling, indicating insufficient stability of the conductive network. Performance testing and characterization

[0039] Pore ​​structure and morphology characterization (BET, SEM, TEM): Nitrogen adsorption-desorption isotherm (BET) testing showed that the porous carbon framework prepared in Example 1 exhibited a typical Type IV adsorption-desorption isotherm, accompanied by a distinct Type H3 hysteresis loop, indicating the presence of abundant mesoporous structures within the material. Its specific surface area reached 1458.28 m² / g, and the total pore volume reached 0.75 cm³ / g. The pore sizes were mainly concentrated around 1.92 nm and 2.07 nm, with micropores accounting for 70.2% of the total pore volume. SEM results showed that the material formed a uniform three-dimensional coral-like network structure, with carbon nanotubes and graphene interwoven to form a continuous conductive framework, and resin-derived carbon uniformly coating the surface of the conductive components.

[0040] Structural Defects and Phase Analysis (XRD, Raman, XPS): The XRD pattern shows distinct silicon characteristic diffraction peaks at 28.4°, 47.3°, and 56.1°, corresponding to the Si(111), Si(220), and Si(311) crystal planes, respectively. A broad (002) peak of carbon material is retained near 23°, indicating the simultaneous presence of crystalline silicon and amorphous carbon structures in the material. Raman spectroscopy results show D and G peaks at approximately 1350 cm⁻¹ and 1580 cm⁻¹, respectively, with an ID / IG value of 0.7, indicating a high defect density and abundant edge active sites, which is beneficial for the adsorption and cracking of silane gas and silicon nucleation and deposition. XPS analysis shows that the material mainly contains C, O, and Si elements. The Si 2p spectrum shows distinct silicon characteristic peaks in the range of approximately 99–103 eV, proving that silicon was successfully deposited on the porous carbon framework surface.

[0041] Electrochemical performance testing was conducted using CR2032 coin cells prepared from the silicon-carbon composite materials obtained in Example 1 and Comparative Examples 1 and 2. The negative electrode preparation process was as follows: silicon-carbon negative electrode material: conductive agent SP: binder PAA = 8:1:1 (mass ratio), prepared into a slurry, coated onto a copper foil current collector, dried in a 50℃ oven for 30 min, and then dried in a 100℃ vacuum drying oven for 8 h. Half-cell assembly used a lithium foil as the counter electrode. The electrolyte was 1 mol / L LiPF6 dissolved in a mixed solvent of EC / DEC / EMC = 2:3:1, with 5% fluoroethylene carbonate (FEC) added.

[0042] Capacity and initial coulombic efficiency test: The initial charge and discharge test was conducted under 0.1C conditions. The initial discharge specific capacity of the silicon-carbon anode obtained in Example 1 reached 2476.69 mAh / g, and the initial coulombic efficiency reached 82.11%.

[0043] Cyclic performance test: Cyclic test was conducted at a current density of 1C. After 100 cycles, the capacity retention rate of the sample in Example 1 was 83%.

[0044] Rate performance test: The reversible specific capacities of the sample in Example 1 at current densities of 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C were 2446.21, 1907.55, 1477.08, 1195.81, 934.47, and 269.42 mAh / g, respectively. When the current density recovered to 0.1C, the capacity recovery rate reached 90.16%, demonstrating excellent rate performance.

[0045] For full-cell application verification, the silicon-carbon anode obtained in Example 1 was capacity-matched with the high-nickel ternary cathode NCM811, and the N / P ratio was controlled at 1.08 to assemble a pouch full cell. After 150 cycles under a 0.5C charge-discharge regime, the capacity retention rate reached over 80%. This demonstrates that the porous carbon framework can effectively buffer the volume expansion of silicon materials during cycling, meeting the application requirements of power batteries.

[0046] In summary, this invention successfully constructed a three-dimensional hierarchical porous carbon framework reinforced with carbon nanotubes / graphene through hydrothermal in-situ polymerization, effectively solving the problems of uneven silicon deposition, difficulty in suppressing volume expansion, and discontinuous conductive network in existing CVD silicon-carbon anodes. The resulting silicon-carbon anode material exhibits excellent performance in specific capacity, initial coulombic efficiency, cycle stability, and rate performance, demonstrating promising prospects for industrial application.

[0047] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention 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 the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A hydrothermally constructed porous carbon composite framework material suitable for CVD silicon-carbon anodes, characterized in that: The porous carbon composite framework material is mainly composed of carbonized resin-derived carbon, with carbon nanotubes and graphene uniformly dispersed inside; the resin-derived carbon, carbon nanotubes and graphene together construct a three-dimensional interconnected conductive hierarchical porous network; nano-silicon particles are uniformly deposited on the surface and inside the pores of the material.

2. The porous carbon composite framework material according to claim 1, characterized in that, The porous carbon composite framework material has a specific surface area of ​​800~2000 m² / g and a total pore volume of 0.8~2.5 cm³ / g; of which mesopores (2~50 nm) account for 40%~70% of the total pore volume.

3. The porous carbon composite framework material according to claim 1, characterized in that, The mass ratio of carbon nanotubes to graphene is 1:5 to 5:1, and the total mass of the two accounts for 1% to 15% of the total mass of the porous carbon composite framework material.

4. The porous carbon composite framework material according to claim 1 or 2, characterized in that, The mass of the nano-silicon particles accounts for 20% to 60% of the total mass of the final silicon-carbon composite anode material, and the average particle size of the silicon particles is 5 to 50 nm.

5. A method for preparing the porous carbon composite framework material according to any one of claims 1 to 4, characterized in that... Includes the following steps: (1) Melamine, resorcinol, formaldehyde and surfactant are dispersed in a solvent, carbon nanotube and graphene dispersion is added, and stirred to form a uniform precursor mixture. (2) The precursor mixture is placed in a closed reaction vessel and subjected to hydrothermal reaction at 120~200℃ for 6~24 h to induce in-situ sol-gel polymerization of resin on the surface of carbon nanotubes / graphene. (3) After washing and drying the hydrothermal products, carbonize them at 700~1000℃ for 2~6 h under an inert atmosphere; (4) Mix the carbonization product with the activator, activate at 700~900℃ for 1~4 h, wash and dry to obtain a porous carbon composite framework; (5) Place the skeleton in a CVD equipment, introduce silane gas, and deposit it at 400~600℃ for 1~8 h to obtain silicon-carbon anode material.

6. A high-energy-density lithium-ion battery, characterized in that: It comprises a positive electrode, a separator, an electrolyte, and a negative electrode made of any one of the materials described in claims 1 to 4; the battery form includes a pouch cell or a 21700 cylindrical cell.

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