Method for constructing silicon-carbon composite structure through multi-step vapor deposition

Abstract

The invention discloses a method for constructing a silicon-carbon composite structure through multi-step vapor deposition, and the method comprises the following steps: S1, placing a porous carbon base material in a vapor deposition reactor, controlling the temperature of the reactor at 450-550 DEG C, introducing a carbon source gas and a diluent gas into the reactor, and pretreating the porous carbon base material to construct a thin carbon protection layer with the thickness of 10-15 nm; s2, raising the temperature of the reactor to 500-650 DEG C, introducing a mixed gas of a silicon source gas and a carrier gas into the reactor, carrying out a secondary vapor deposition reaction on the porous carbon substrate, and constructing a silicon layer on the thin carbon protection layer; s3, the temperature of the reactor is controlled to be 750-950 DEG C, carbon source gas and diluent gas are introduced into the reactor, vapor deposition reaction is conducted on the porous carbon base material again, an outer carbon layer with the thickness being 15-20 nm is deposited and constructed on the surface of the silicon layer, and a silicon-carbon composite structure is constructed and formed; the silicon-based composite material has a sandwich or gradient structure, the volume expansion stress of silicon is effectively relieved, and the conductivity and mechanical strength of the material are improved.

Description

Technical Field

[0001] This invention relates to the field of vapor phase deposition for preparing battery anode materials, and more particularly to a method for constructing silicon-carbon composite structures through multi-step vapor phase deposition. Background Technology

[0002] Anode materials are the electrodes in batteries that perform oxidation, storing and releasing lithium / sodium ions, directly affecting battery capacity, cycle life, and other performance characteristics. Based on their working principle, they can be classified into four types: intercalation / deintercalation type (e.g., graphite), conversion type (e.g., metal oxides), alloy type (e.g., silicon-based), and deposition type (e.g., lithium metal). The demand for higher energy density in lithium-ion batteries has driven research into high-capacity anode materials, with silicon being an ideal choice due to its high theoretical specific capacity, but it faces challenges such as volume expansion and poor conductivity. Chemical vapor deposition (CVD) effectively suppresses silicon particle expansion and improves conductivity through the confinement effect of a porous carbon matrix, becoming a cutting-edge preparation technology. However, existing methods have shortcomings in deposition kinetics control and structural stability, leading to limitations in material cycle performance. Summary of the Invention

[0003] The purpose of this invention is to provide a method for constructing silicon-carbon composite structures through multi-step vapor deposition, in order to solve the problems mentioned in the background art, such as the deficiencies in the preparation of existing lithium battery anode materials in terms of deposition kinetics control and structural stability.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a method for constructing silicon-carbon composite structures via multi-step vapor deposition, the method comprising the following steps: S1. Place the porous carbon substrate in a vapor deposition reactor, control the reactor temperature to 450~550℃, and then introduce carbon source gas and dilution gas into the reactor to pretreat the porous carbon substrate and construct a thin carbon protective layer with a thickness of 10~15nm. S2. Raise the reactor temperature to 500~650℃, and then introduce a mixture of silicon source gas and carrier gas into the reactor to perform a secondary vapor phase deposition reaction on the porous carbon substrate, and build a silicon layer on the thin carbon protective layer. S3. Control the reactor temperature to 750~950℃, then introduce carbon source gas and dilution gas into the reactor to perform another vapor phase deposition reaction on the porous carbon substrate, deposit an outer carbon layer with a thickness of 15~20nm on the silicon layer surface, and finally construct a silicon-carbon composite structure. In steps S1 and S3, the carbon source gas is one or more of methane, ethylene, or acetylene, and the dilution gas is one or more of nitrogen, argon, or neon. In step S1, the volume ratio of the carbon source gas to the dilution gas is 1:2 to 1:5, and in step S3, the volume ratio of the carbon source gas to the dilution gas is 1:3 to 1:8.

[0005] Preferably, the pretreatment time for the porous carbon substrate in step S1 is 1-2 hours, the secondary vapor deposition reaction time in step S2 is 2-4 hours, and the re-vapor deposition reaction time in step S3 is 1-3 hours.

[0006] Preferably, the vapor deposition reactions in steps S1 and S3 are carried out under low pressure conditions of 0.01~0.15 MPa.

[0007] Preferably, in step S2, the silicon source gas is one or more of silane, dichlorosilane, or trichlorosilane, and the carrier gas is one or more of argon, helium, hydrogen, or argon, with the silicon source gas accounting for 1 to 10% of the mixed gas.

[0008] Preferably, step S2 includes the following multiple reaction stages, In the first stage, the concentration of silicon source gas is controlled at 1-5%, the reaction pressure at 0.01-0.05 MPa, the gas flow rate at 0.5-1 L / min, the temperature at 500-550℃, and the duration at 0.5-1.5 h. In the second stage, the concentration of silicon source gas is controlled at 5-10%, the reaction pressure at 10-100 Pa, the gas flow rate at 1-2 L / min, the temperature at 550-650℃, and the duration is 1-3 hours. In the third stage, the concentration of silicon source gas is controlled at 1-5%, the reaction pressure is 0.01-0.05 MPa, the gas flow rate is 0.5-1 L / min, the temperature is 500-550℃, and the duration is 0.5-1.5 h.

[0009] Preferably, in step S2, the silicon layer has a "sandwich" or "gradient" structure, wherein the silicon particles are 8-35 nm in size and are uniformly dispersed in the pores and surface of the porous carbon substrate.

[0010] Preferably, during the vapor deposition reaction in steps S1 and S3, the gas flow rate is 1~1.5L / min.

[0011] Preferably, in step S3, the carbon source gas and the doping gas are mixed and introduced, and the doping gas is one or more of diborane or phosphine, with the proportion of the doping gas being 0.1% to 1%.

[0012] Preferably, the porous carbon substrate has a specific surface area of ​​1800~2500m² / g, a multi-level pore structure with micropores, mesopores and macropores, and a porosity of 65~75%.

[0013] A silicon-carbon composite structure having a multi-level buffer layer, including an inner thin carbon protective layer, an intermediate silicon layer and an outer hard carbon layer gradient coating structure, is used as a negative electrode material for lithium-ion batteries.

[0014] The beneficial effects of this invention are: This invention constructs a silicon layer through multiple reaction stages, giving it a "sandwich" or "gradient" structure that is uniformly dispersed in the pores and surface of a porous carbon substrate. This effectively alleviates the volume expansion stress of silicon and improves the material's conductivity and mechanical strength. Furthermore, by constructing a silicon-carbon composite structure with multi-level buffer layers, the specific capacity and cycle stability of lithium-ion batteries are significantly improved. By using the silicon-carbon composite structure as the negative electrode of lithium-ion batteries, it combines high specific capacity and long cycle life, meeting the requirements of fast charging and high power output.

[0015] By constructing a thin carbon protective layer of 10~15nm, the volume expansion of silicon during charging and discharging can be effectively buffered by about 300%, preventing electrode pulverization. By constructing an outer carbon layer of 15~20nm, the silicon layer is further wrapped to form a stable protective shell, which together maintains the integrity of the electrode structure and significantly improves cycle life.

[0016] By selecting porous carbon substrates with a specific surface area of ​​1800~2500m² / g and a porosity of 65~75%, the interfacial bonding force between silicon and carbon matrix is ​​enhanced, effectively suppressing the shedding of silicon particles during charging and discharging, thereby improving the cycle stability of the material. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the steps of constructing a silicon-carbon composite structure by vapor deposition according to the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Please see Figure 1 A method for constructing silicon-carbon composite structures via multi-step vapor deposition, the method comprising the following steps: S1. Place the porous carbon substrate in a vapor deposition reactor, control the reactor temperature to 450~550℃, and then introduce carbon source gas and dilution gas into the reactor to pretreat the porous carbon substrate and construct a thin carbon protective layer with a thickness of 10~15nm. S2. Raise the reactor temperature to 500~650℃, and then introduce a mixture of silicon source gas and carrier gas into the reactor to perform a secondary vapor phase deposition reaction on the porous carbon substrate, and build a silicon layer on the thin carbon protective layer. S3. Control the reactor temperature to 750~950℃, then introduce carbon source gas and dilution gas into the reactor to perform another vapor phase deposition reaction on the porous carbon substrate, deposit an outer carbon layer with a thickness of 15~20nm on the silicon layer surface, and finally construct a silicon-carbon composite structure. In steps S1 and S3, the carbon source gas is one or more of methane, ethylene, or acetylene, and the dilution gas is one or more of nitrogen, argon, or neon. In step S1, the volume ratio of the carbon source gas to the dilution gas is 1:2 to 1:5, and in step S3, the volume ratio of the carbon source gas to the dilution gas is 1:3 to 1:8.

[0020] Specifically, a thin carbon protective layer of 10-15nm can effectively buffer the approximately 300% volume expansion of silicon during charging and discharging, preventing electrode pulverization. An outer carbon layer of 15-20nm further encapsulates the silicon layer, forming a stable protective shell that together maintains the integrity of the electrode structure, significantly improving cycle life. The dense carbon layer also helps to form a thin and stable SEI film, reducing electrolyte decomposition and irreversible lithium loss, improving the battery's initial coulombic efficiency and long-term cycle stability. Through a "sandwich" or "gradient" structural design, the high capacity of silicon and the stability of carbon are combined.

[0021] Specifically, the pretreatment time for the porous carbon substrate in step S1 is 1-2 hours, the secondary vapor deposition reaction time in step S2 is 2-4 hours, and the re-vapor deposition reaction time in step S3 is 1-3 hours. By controlling the 1-2 hours of pretreatment of the porous carbon substrate, the 2-4 hours of multi-stage vapor deposition to build the silicon layer, and the 1-3 hours of vapor deposition to build the outer carbon layer, it is ensured that the carbon layer uniformly covers the surface of the porous carbon substrate, avoiding insufficient protection due to an excessively thin layer structure, or increased internal stress due to an excessively thick layer structure.

[0022] Specifically, the vapor deposition reactions in steps S1 and S3 are carried out under low pressure conditions of 0.01~0.15 MPa. Under low pressure, the gas diffusion behavior is more controllable, which can better cover complex surfaces (such as deep pores and fine pores of porous carbon substrates) and achieve uniform deposition. At the same time, it can also reduce the amount of carrier gas used, increase the partial pressure of the reaction gas, improve deposition efficiency and reduce costs while ensuring quality.

[0023] Specifically, in step S2, the silicon source gas is one or more of silane, dichlorosilane, or trichlorosilane, and the carrier gas is one or more of argon, helium, hydrogen, or argon. The proportion of silicon source gas in the mixed gas is 1-10%.

[0024] Specifically, step S2 includes the following multiple reaction stages: In the first stage, the concentration of silicon source gas is controlled at 1-5%, the reaction pressure at 0.01-0.05 MPa, the gas flow rate at 0.5-1 L / min, the temperature at 500-550℃, and the duration at 0.5-1.5 h. In the second stage, the concentration of silicon source gas is controlled at 5-10%, the reaction pressure at 10-100 Pa, the gas flow rate at 1-2 L / min, the temperature at 550-650℃, and the duration is 1-3 hours. In the third stage, the concentration of silicon source gas is controlled at 1-5%, the reaction pressure at 0.01-0.05 MPa, the gas flow rate at 0.5-1 L / min, the temperature at 500-550℃, and the duration at 0.5-1.5 h. By controlling the gas-phase reaction parameters in the first and third stages, the silicon source gas is kept at a low concentration (e.g., 1-5%), which reduces the generation of byproducts such as silicon carbide (SiC) and avoids an increase in interfacial impedance. By controlling the gas-phase reaction parameters in the second stage, the silicon source gas is kept at a medium-high concentration (5-10%), which ensures a dense silicon layer coverage, prevents local thinning or agglomeration, and achieves a cycle life of more than 1000 cycles. The silicon layer construction is carried out by adjusting the silicon source gas concentration in stages to build a "sandwich" structure, which reduces the cell expansion rate by 30% and achieves synergistic optimization of high capacity (>1800mAh / g) and long cycle life of lithium batteries.

[0025] Specifically, in step S2, the silicon layer has a "sandwich" or "gradient" structure, wherein the silicon particles are 8~35nm in size and are uniformly dispersed in the pores and surface of the porous carbon substrate. The 8~35nm silicon particle size ensures high specific capacity, while the nano-size effect also alleviates the volume expansion problem, thus significantly improving the energy density of the lithium battery.

[0026] Specifically, during the vapor deposition reaction in steps S1 and S3, the gas flow rate is 1~1.5L / min to balance the supply of carbon source gas and dilution gas with the deposition reaction efficiency of porous carbon substrate, avoiding insufficient deposition due to too low a flow rate or incomplete reaction due to too high a flow rate.

[0027] Specifically, in step S3, the carbon source gas and the doping gas are mixed and introduced. The doping gas is one or more of diborane or phosphine, and the proportion of the doping gas is 0.1% to 1%. By doping a small amount of diborane and / or phosphine, the electronic conductivity of the deposited outer carbon layer is significantly improved and the contact resistance is reduced.

[0028] Specifically, the porous carbon substrate has a specific surface area of ​​1800~2500m² / g, a multi-level pore structure with micropores, mesopores and macropores, and a porosity of 65~75%. By selecting a porous carbon substrate with a specific surface area of ​​1800~2500m² / g and a porosity of 65~75%, the interfacial bonding force between silicon and carbon matrix is ​​enhanced, effectively suppressing the shedding of silicon particles during charging and discharging, thereby improving the cycle stability of the material.

[0029] A silicon-carbon composite structure having a multi-level buffer layer, including an inner thin carbon protective layer, an intermediate silicon layer and an outer hard carbon layer gradient coating structure, is used as a negative electrode material for lithium-ion batteries.

[0030] Example 1: S1. A porous carbon substrate is placed in a vapor deposition reactor. The reactor temperature is controlled at 480°C. Under a low pressure of 0.01 MPa, carbon source gas and dilution gas are introduced into the reactor with a volume ratio of 1:2.5. The gas flow rate is controlled at 1 L / min. The porous carbon substrate is pretreated for 1 hour to form a thin carbon protective layer with a thickness of 10 nm. S2. Then, a mixture of silicon source gas and carrier gas is introduced into the reactor in multiple stages. In the first stage, the concentration of silicon source gas is controlled at 1.5%, the reaction pressure is 0.01 MPa, the gas flow rate is 0.5 L / min, the temperature is 500℃, and the duration is 0.8 h. In the second stage, the concentration of silicon source gas was controlled at 5%, the reaction pressure at 30 Pa, the gas flow rate at 1 L / min, the temperature at 550℃, and the duration was 2 hours. In the third stage, the concentration of silicon source gas was controlled at 1.5%, the reaction pressure at 0.01 MPa, the gas flow rate at 0.5 L / min, the temperature at 500 °C, and the duration at 0.8 h. Finally, a silicon layer with a "sandwich" or "gradient" structure was constructed on the thin carbon protective layer. S3. Control the reactor temperature to 780℃. Under low pressure of 0.01Mpa, introduce carbon source gas and dilution gas into the reactor with a volume ratio of 1:4. The carbon source gas contains diborane, and the proportion of diborane in the carbon source gas mixture is 0.3%. Control the gas flow rate to 1 L / min. Perform a second vapor-phase deposition reaction on the porous carbon substrate for 1 hour to deposit an outer carbon layer with a thickness of 15nm on the silicon layer surface, and finally construct a silicon-carbon composite structure. Example 2: S1. The porous carbon substrate is placed in a vapor deposition reactor, the reactor temperature is controlled at 500°C, and under a low pressure of 0.1 MPa, carbon source gas and dilution gas are introduced into the reactor with a volume ratio of 1:4. The gas flow rate is controlled at 1 L / min. The porous carbon substrate is pretreated for 1.5 h to construct a thin carbon protective layer with a thickness of 12 nm. S2. Then, a mixture of silicon source gas and carrier gas is introduced into the reactor in multiple stages. In the first stage, the concentration of silicon source gas is controlled at 3%, the reaction pressure is 0.03 MPa, the gas flow rate is 0.5 L / min, the temperature is 530℃, and the duration is 1 hour. In the second stage, the concentration of silicon source gas was controlled at 8%, the reaction pressure at 50 Pa, the gas flow rate at 1.5 L / min, the temperature at 600℃, and the duration was 2 hours. In the third stage, the concentration of silicon source gas was controlled at 3%, the reaction pressure at 0.03 MPa, the gas flow rate at 0.5 L / min, the temperature at 550 °C, and the duration at 0.8 h. Finally, a silicon layer with a "sandwich" or "gradient" structure was constructed on the thin carbon protective layer. S3. Control the reactor temperature to 850℃, and under a low pressure of 0.1 MPa, introduce carbon source gas and dilution gas into the reactor with a volume ratio of 1:6. The carbon source gas contains phosphine, and the proportion of phosphine in the carbon source gas mixture is 0.5%. Control the gas flow rate to 1 L / min, and perform a second vapor-phase deposition reaction on the porous carbon substrate for 2 hours to deposit an outer carbon layer with a thickness of 18 nm on the silicon layer surface, and finally construct a silicon-carbon composite structure. Example 3: S1. The porous carbon substrate is placed in a vapor deposition reactor, the reactor temperature is controlled at 550°C, and under a low pressure of 0.15 MPa, carbon source gas and dilution gas are introduced into the reactor with a volume ratio of 1:5. The gas flow rate is controlled at 1.5 L / min. The porous carbon substrate is pretreated for 1.5 h to construct a thin carbon protective layer with a thickness of 15 nm. S2. Then, a mixture of silicon source gas and carrier gas is introduced into the reactor in multiple stages. In the first stage, the concentration of silicon source gas is controlled at 5%, the reaction pressure is 0.05 MPa, the gas flow rate is 1 L / min, the temperature is 550℃, and the duration is 1 h. In the second stage, the concentration of silicon source gas was controlled at 10%, the reaction pressure at 50 Pa, the gas flow rate at 2 L / min, the temperature at 650 °C, and the duration was 2 h. In the third stage, the concentration of silicon source gas was controlled at 5%, the reaction pressure at 0.05 MPa, the gas flow rate at 1 L / min, the temperature at 550 °C, and the duration at 1 h. Finally, a silicon layer with a "sandwich" or "gradient" structure was constructed on the thin carbon protective layer. S3. Control the reactor temperature at 900℃ and under a low pressure of 0.15 MPa, introduce carbon source gas and dilution gas into the reactor with a volume ratio of 1:8. The carbon source gas contains diborane, and the proportion of diborane in the carbon source gas mixture is 0.8%. Control the gas flow rate at 1.5 L / min and perform a second vapor-phase deposition reaction on the porous carbon substrate for 3 hours to deposit an outer carbon layer with a thickness of 20 nm on the silicon layer surface, thus finally forming a silicon-carbon composite structure. Comparative Example 1 uses graphene as the negative electrode material for lithium batteries.

[0031] Comparative Example 2 uses a tin-based alloy as the negative electrode material for lithium batteries.

[0032] Performance comparison of Examples 1, 2, and 3 and Comparative Examples 1 and 2 as battery anode materials (as shown in Table 1): Table 1

[0033] As shown in Table 1, the silicon-carbon composite structure constructed by the present invention has better performance than graphene and tin-based alloys as a negative electrode material for lithium batteries. Furthermore, as the thickness of the multi-level buffer layer, including the inner thin carbon protective layer, the middle silicon layer and the outer hard carbon layer, increases, its performance becomes even better. For example, the silicon-carbon composite structure prepared in Example 3 has better performance than that in Examples 1 and 2.

[0034] 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 or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for constructing silicon-carbon composite structures via multi-step vapor deposition, characterized in that, The method includes the following steps: S1. Place the porous carbon substrate in a vapor deposition reactor, control the reactor temperature to 450~550℃, and then introduce carbon source gas and dilution gas into the reactor to pretreat the porous carbon substrate and construct a thin carbon protective layer with a thickness of 10~15nm. S2. Raise the reactor temperature to 500~650℃, and then introduce a mixture of silicon source gas and carrier gas into the reactor to perform a secondary vapor phase deposition reaction on the porous carbon substrate, and build a silicon layer on the thin carbon protective layer. S3. Control the reactor temperature to 750~950℃, then introduce carbon source gas and dilution gas into the reactor to perform another vapor phase deposition reaction on the porous carbon substrate, deposit an outer carbon layer with a thickness of 15~20nm on the silicon layer surface, and finally construct a silicon-carbon composite structure. In steps S1 and S3, the carbon source gas is one or more of methane, ethylene, or acetylene, and the dilution gas is one or more of nitrogen, argon, or neon. In step S1, the volume ratio of the carbon source gas to the dilution gas is 1:2 to 1:5, and in step S3, the volume ratio of the carbon source gas to the dilution gas is 1:3 to 1:

8.

2. The method for constructing silicon-carbon composite structures via multi-step vapor deposition according to claim 1, characterized in that, The pretreatment time for the porous carbon substrate in step S1 is 1-2 hours, the secondary vapor deposition reaction time in step S2 is 2-4 hours, and the re-vapor deposition reaction time in step S3 is 1-3 hours.

3. The method for constructing silicon-carbon composite structures via multi-step vapor deposition according to claim 1, characterized in that, The vapor deposition reactions in steps S1 and S3 are carried out under low pressure conditions of 0.01~0.15 MPa.

4. The method for constructing silicon-carbon composite structures via multi-step vapor deposition according to claim 1, characterized in that, In step S2, the silicon source gas is one or more of silane, dichlorosilane, or trichlorosilane, and the carrier gas is one or more of argon, helium, or hydrogen. The proportion of silicon source gas in the mixed gas is 1-10%.

5. The method for constructing silicon-carbon composite structures via multi-step vapor deposition according to claim 1, characterized in that, Step S2 includes the following multiple reaction stages. In the first stage, the concentration of silicon source gas is controlled at 1-5%, the reaction pressure at 0.01-0.05 MPa, the gas flow rate at 0.5-1 L / min, the temperature at 500-550℃, and the duration at 0.5-1.5 h. In the second stage, the concentration of silicon source gas is controlled at 5-10%, the reaction pressure at 10-100 Pa, the gas flow rate at 1-2 L / min, the temperature at 550-650℃, and the duration is 1-3 hours. In the third stage, the concentration of silicon source gas is controlled at 1-5%, the reaction pressure is 0.01-0.05 MPa, the gas flow rate is 0.5-1 L / min, the temperature is 500-550℃, and the duration is 0.5-1.5h.

6. The method for constructing silicon-carbon composite structures via multi-step vapor deposition according to claim 1, characterized in that, In step S2, the silicon layer has a "sandwich" or "gradient" structure, wherein the silicon particles are 8-35 nm in size and are uniformly dispersed in the pores and surface of the porous carbon substrate.

7. The method for constructing silicon-carbon composite structures via multi-step vapor deposition according to claim 1, characterized in that, During the vapor deposition reaction in steps S1 and S3, the gas flow rate is 1~1.5L / min.

8. The method for constructing silicon-carbon composite structures via multi-step vapor deposition according to claim 1, characterized in that, In step S3, the carbon source gas and the dopant gas are mixed and introduced. The dopant gas is one or more of diborane or phosphine, and the proportion of the dopant gas is 0.1% to 1%.

9. The method for constructing silicon-carbon composite structures via multi-step vapor deposition according to claim 1, characterized in that, The porous carbon substrate has a specific surface area of ​​1800~2500m² / g, a multi-level pore structure with micropores, mesopores and macropores, and a porosity of 65~75%.

10. A silicon-carbon composite structure, characterized in that, The silicon-carbon composite structure is prepared by the multi-step vapor deposition method described in any one of claims 1 to 9. The silicon-carbon composite structure has a multi-level buffer layer, including a gradient coating structure of an inner thin carbon protective layer, an intermediate silicon layer and an outer hard carbon layer, and is used as a negative electrode material for lithium-ion batteries.

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