CN107768640B - Crystalline/amorphous silicon-carbon nanowire and preparation method and application thereof - Google Patents

Crystalline/amorphous silicon-carbon nanowire and preparation method and application thereof Download PDF

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CN107768640B
CN107768640B CN201710978965.1A CN201710978965A CN107768640B CN 107768640 B CN107768640 B CN 107768640B CN 201710978965 A CN201710978965 A CN 201710978965A CN 107768640 B CN107768640 B CN 107768640B
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amorphous silicon
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袁方利
侯果林
程本立
金化成
杜宇
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Institute of Process Engineering of CAS
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Abstract

The invention discloses a crystallization/amorphous silicon-carbon nanowire and a preparation method and application thereof, belonging to the field of lithium ion batteries. The crystalline silicon core, the amorphous silicon layer and the carbon outer layer jointly form a three-level structure composite material system: the crystalline silicon nucleus mainly plays a supporting role; amorphous silicon dominates the lithium storage function; carbon is at the outermost layer and plays a role in forming a stable SEI film and improving the coulombic efficiency. The invention is characterized in that the crystal/amorphous silicon nano-wire is prepared by one step method by utilizing the characteristics of high temperature and rapid cooling of the thermal plasma, and meanwhile, the high-purity quality of the product is ensured by the electrodeless heating characteristic of the thermal plasma. The method has the advantages of simple process, environment-friendly process, low cost, continuity and controllability, and capability of realizing macro preparation. The crystalline/amorphous silicon-carbon nanowire prepared by the invention is used as the lithium ion battery cathode, has small volume change and stable structure in the lithium intercalation/deintercalation process, and effectively improves the energy density and the cycling stability of the lithium ion battery cathode material.

Description

Crystalline/amorphous silicon-carbon nanowire and preparation method and application thereof
Technical Field
The invention relates to a lithium ion battery cathode material, a preparation method and application, and belongs to the field of lithium ion batteries. In particular to a crystalline/amorphous silicon-carbon nanowire gradient buffer composite material which can be used as a lithium ion battery cathode and has high specific capacity and high coulombic efficiency, a preparation method and application thereof.
Background
Energy of lithium ion battery for rapid development of portable electronic products and new energy power automobilesDensity puts higher demands on it. The traditional graphite cathode has lower theoretical specific capacity (372mA h g)-1) It has been difficult to meet the energy density requirements of lithium batteries. The silicon negative electrode material has higher theoretical lithium storage specific capacity (4200 mAhg)-1) And a lower intercalation potential (-0.2V), are considered to be one of the most promising high performance lithium battery negative electrode materials. However, the volume change of the silicon material is as high as 300% in the charging and discharging processes, the active material is cracked and falls off due to the huge volume effect, a stable Solid Electrolyte Interface (SEI) film is difficult to form on the surface, the coulombic efficiency is reduced, the cycle performance of the electrode material is rapidly attenuated, and the application of the electrode material in the lithium ion battery is severely limited.
Aiming at the problem of volume expansion of a silicon-based negative electrode material in the charging and discharging process, the volume expansion of the silicon-based negative electrode material is mainly inhibited by preparing silicon nano materials and silicon-carbon composite materials with different structures at present, and the key point for preparing the silicon-carbon composite material lies in the construction of the silicon nano structure. The one-dimensional nanowire can reduce the volume expansion of silicon in the radial direction and can provide Li in the axial direction+The rapid transmission channel is beneficial to improving the stability and electrochemical performance of the electrode structure, and is considered to be an effective way for solving the problem of the silicon-based lithium ion battery. Literature reports find that crystalline silicon nanowires have faster Li+Migration rate and good mechanical support, which is favorable for the promotion of rate capability [ J Phys Chem C,2015,119, 3447-3455; nano Energy,2013,2,943-]. However, the volume expansion of the crystalline silicon nanowire is anisotropic and uneven in the charge and discharge processes, so that the structural stability of silicon is poor, and the stability of long-term circulation is difficult to maintain. The amorphous silicon nanowire has isotropic volume expansion in the charging and discharging processes, is not easy to cause material fracture and pulverization, and has relatively small volume expansion and higher flexibility [ J Phys Chem C,2011,115, 2514-; nano Lett.,2013,13,709-]. Therefore, the preparation of the crystalline/amorphous core-shell structure silicon nanowire has great advantage in improving the cycling stability of the silicon cathode by combining the characteristics of the crystalline silicon and the amorphous silicon nanowire.
At present, the methods for preparing silicon nanowires mainly include chemical vapor deposition, laser ablation, electron beam evaporation, magnetron sputtering, and metal-assisted chemical etching. However, the silicon nanowires obtained by the preparation methods are mainly single-structure silicon nanowires, namely crystalline silicon nanowires or amorphous silicon nanowires. In addition, the preparation methods mainly use silane or silicon tetrachloride as a silicon source, and generally have the problems of high raw material cost, complex preparation process, high equipment requirement, harsh process conditions, serious pollution, difficult large-scale production and the like. In addition, metal particles are usually used as catalysts in the preparation process, so that pollution is brought to materials, and the specific capacity of the composite material is reduced. Therefore, a preparation method which is simple and environment-friendly in process and can synthesize a large amount of silicon nanowires is urgently needed.
Disclosure of Invention
In view of the above problems in the prior art, an object of the present invention is to provide a crystalline/amorphous silicon-carbon nanowire gradient buffer composite material, which can reduce the volume expansion of silicon and improve the energy density and the cycling stability of a silicon-based negative electrode material of a lithium ion battery. The invention also aims to provide a method for preparing the composite material, in particular to a method for preparing crystalline/amorphous core-shell silicon nanowires by using thermal plasma, which has the advantages of simple process, environment-friendly process, low cost, continuity and controllability, and capability of realizing macro preparation and promoting the practical application of silicon-based cathode materials.
In order to achieve the purpose, the invention adopts the following technical scheme:
providing a crystalline/amorphous silicon-carbon nanowire which sequentially comprises a crystalline silicon core, an amorphous silicon layer and a carbon outer layer from inside to outside, wherein the crystalline silicon and the amorphous silicon form the silicon nanowire, and a carbon layer is coated on the outer surface of the silicon nanowire to jointly form a three-level structure composite material system; the crystalline silicon nucleus mainly plays a supporting role, the amorphous silicon mainly plays a role in storing lithium, and the carbon plays a role in forming a stable SEI film to improve the coulombic efficiency at the outermost layer.
The mass ratio of the crystalline/amorphous silicon to the composite material is between 5 and 95 percent. The diameter of the silicon nanowire is 10 nm-100 nm, and the thickness of the carbon layer is 5 nm-50 nm.
Provided is a method for preparing a crystalline/amorphous silicon-carbon nanowire, including preparing a crystalline/amorphous silicon nanowire by a thermal plasma; and depositing a carbon layer on the surface of the crystalline/amorphous silicon nanowire.
The preparation of amorphous/crystalline silicon nanowires by means of a thermal plasma specifically comprises the following steps:
(1) the thermal plasma generating device generates stable thermal plasma;
(2) delivering silicon powder to the thermal plasma region by using argon or hydrogen as a carrier gas: the particle diameter of the silicon powder is 1-300 μm, the feeding rate is 1-100 g/min, and the carrier gas flow is 0-5m3The silicon powder is gasified and condensed in the thermal plasma area to form a crystalline silicon core;
(3) the crystalline silicon inner core leaves the hot plasma area and enters the plasma shape regulator under the drive of the air flow: amorphous silicon is deposited on the surface of the amorphous silicon film and grows to form amorphous/crystalline silicon nanowires;
(4) the amorphous/crystalline silicon nanowires enter the product collection system under gas transport.
And (4) the shape regulator in the step (3) is a graphite inner sleeve-stainless steel outer shell double-layer closed sleeve, and the graphite inner sleeve can strengthen the high-temperature region of the plasma, regulate and control the temperature gradient and prolong the deposition time of amorphous silicon in the low-temperature region.
The carbon layer deposited on the surface of the crystalline/amorphous silicon nanowire is performed by carbon-containing gas chemical vapor deposition or carbon-containing organic matter heat treatment.
The carbon-containing gas is any one or more of methane, ethane, acetylene, ethylene, propane, propylene and propyne;
the carbon-containing organic matter is any one or more of glucose, sucrose, fructose, maltose, galactose, lactose, phenolic resin, epoxy resin, naphthalene resin, cellulose resin, resorcinol resin, coal-derived asphalt, petroleum-derived asphalt and coke.
The heat treatment temperature is 500-1500 ℃, and the time is 2-24 h.
The most prominent characteristic of the invention is that the thermal plasma is adopted to prepare the crystal/amorphous silicon nano-wire. The thermal plasma has the characteristics of high temperature and quick cooling, and the graphite inner sleeve-stainless steel outer shell double-layer closed sleeve can strengthen the high-temperature area of the plasma, effectively regulate and control the temperature gradient and prolong the silicon nucleus deposition time in the low-temperature area. From literature reports, high temperature and high vapor pressure favor the formation of crystalline silicon, while low temperature and low pressure favor the deposition of amorphous silicon [ j. mater. chem.a,2013,1, 9566; nano lett, 2009,9,491 ]. In the process of preparing the crystalline/amorphous silicon nanowire by using the thermal plasma, reaction raw materials enter a plasma high-temperature high-pressure area under the drive of carrier gas, and the raw materials are rapidly decomposed, gasified and rapidly condensed to form a crystalline inner core; when the material is transported to a low-temperature and low-pressure area, an amorphous shell is obtained by deposition on the surface of the material. Therefore, the thermal plasma can realize one-step regulation and control to prepare the crystalline/amorphous core-shell structure silicon nanowire.
The inventor of the invention can regulate and control the vapor pressure and the retention time in the plasma by changing the feeding speed of the silicon source and the carrier gas flow through a series of exploration to obtain the silicon nanowires with different diameters, lengths and amorphous silicon thicknesses, and obtains a proper feeding speed of 1-100 g/min, preferably 5-30 g/min through a plurality of times of experimental exploration; obtaining a suitable carrier gas velocity of 0-5m3H, preferably 1.0 to 3m3H is used as the reference value. In addition, the preparation of the nano material by the thermal plasma is continuous and controllable, and macroscopic preparation can be realized, which has important significance for promoting the practical application of the silicon-based negative electrode material.
The crystalline/amorphous silicon-carbon nanowire three-level structure composite material obtained by the invention has the characteristic of gradient buffer volume effect. The crystalline silicon nucleus in the composite material mainly plays a supporting role; amorphous silicon with small volume change has a dominant lithium storage effect; carbon is arranged on the outermost layer, so that the volume expansion of internal silicon is buffered, a stable SEI film is formed, the coulombic efficiency is improved, and the conductivity of the composite material is improved. Meanwhile, the abundant pore structures among the silicon-carbon nanowires can further buffer the volume expansion of silicon in the lithium intercalation process. The three-level gradient buffer structure of the silicon-carbon nanowire composite material ensures that the electrode material has smaller volume expansion (the diameter is expanded by only 7 percent after circulation) in the circulation process, and can form a stable SEI film. Therefore, compared with the traditional silicon anode material, the material obtained by the invention has more excellent cycle stabilityAnd rate capability. The first coulombic efficiency (ICE) of the crystallized/amorphous silicon-carbon nanowire is 89.6 percent, and the first specific capacity is as high as 2433mA h g -16 times of the theoretical capacity of graphite; meanwhile, the material shows excellent rate performance, and the current density is 4200mA g-1(1.0C), the composite material still shows higher capacity and cycling stability, and after 200 cycles, the specific capacity is 1286mA h g-1(ii) a At high current densities of 2.0C and 3.0C, the specific capacities were still 854 and 625mA h g, respectively-1Far superior to the theoretical capacity of graphite.
The method has the characteristics of simple process, environment-friendly process, low cost, continuity and controllability, can realize macroscopic quantity preparation, solves the problems of high production cost, complex process, serious pollution, difficult large-scale production and the like of the silicon nanowire material, and can promote the practical application of the silicon-based cathode material.
Drawings
Fig. 1a is a schematic view of a crystalline/amorphous silicon-carbon nanowire composite according to the present invention. Wherein: crystalline silicon core, amorphous silicon layer and carbon outer layer. FIG. 1b is a schematic diagram of the lithium intercalation process of the amorphous silicon-carbon nanowire according to the present invention.
FIG. 2 is a schematic view of a plasma apparatus used in the preparation of crystalline/amorphous silicon nanowires according to the present invention. Wherein: central gas, side gas, plasma generator, controller for shape and appearance, ninthly collecting cylinder and emptying system for the R.
Figure 3 is a scanning electron micrograph of crystalline/amorphous silicon nanowires prepared according to one embodiment of the present invention.
Figure 4 is a transmission electron micrograph of a crystalline/amorphous silicon nanowire prepared according to one embodiment of the present invention.
Figure 5 is a transmission electron micrograph of crystalline/amorphous silicon-carbon nanowires prepared according to one embodiment of the present invention.
Figure 6 is a graph illustrating the cycling performance for the preparation of crystalline/amorphous silicon-carbon nanowires according to one embodiment of the present invention.
Figure 7 is a graph of rate capability for fabricating crystalline/amorphous silicon-carbon nanowires according to one embodiment of the present invention.
Detailed Description
In order to better explain the present invention and to facilitate a full understanding of the technical solutions of the present invention, the technical solutions of the present invention are described in detail below by specific embodiments with reference to the accompanying drawings. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
Preparation of crystalline/amorphous silicon nanowires:
a10 kW thermal plasma device is adopted to prepare the crystalline/amorphous silicon-carbon nanowires, and the device mainly comprises a 10kW plasma generation system, a feeding system, a graphite inner sleeve-stainless steel shell double-layer regulator, a gas distribution system, a product collection system, a tail gas discharge system and the like. The raw material silicon powder is commercially available micron silicon powder with the particle size of 5 microns. Introducing central gas (argon) into the plasma device, after the plasma arc is formed and stably operates for 3 minutes, adding silicon powder through a feeder, wherein the feeding speed is 5g/min, the carrier gas is argon, and the carrier gas speed is 0.5m3H is used as the reference value. And (3) extinguishing the arc after stopping feeding, and collecting to obtain the crystalline/amorphous silicon nanowire with the diameter of 30-50nm and the length of 500 nm.
Preparation of crystalline/amorphous silicon-carbon nanowires:
dissolving 10g of glucose in deionized water, adding 50g of the prepared silicon nanowire under the stirring condition, and stirring and ultrasonically treating to obtain uniformly dispersed suspension; and (3) carrying out spray drying on the turbid liquid to obtain a precursor of the silicon-carbon nanowire, wherein the spray drying conditions are as follows: the inlet temperature was 230 ℃, the outlet temperature was 110 ℃ and the cyclone amount was 100%. And placing the obtained precursor composite material of the silicon-carbon nanowire in a tube furnace, preserving the heat for 3h at 800 ℃ in argon atmosphere, and naturally cooling to room temperature to obtain the crystalline/amorphous silicon-carbon nanowire, wherein the silicon content is 93%, the carbon content is 7%, and the thickness of the carbon layer is 10 nm.
And (3) performance detection:
the crystalline/amorphous silicon-carbon nanowires prepared in the examples are used as negative electrode materials to assemble batteries, and the electrochemical performance of the batteries is tested, and the specific steps are as follows:
(1) pulping: weighing the negative electrode material, the conductive agent and the binder according to the ratio of 8:1:1, adding a solvent to adjust the viscosity of the slurry, and stirring for 3-5 hours.
(2) Coating: the slurry was coated on a copper foil current collector with a doctor blade mold.
(3) And (3) drying: drying at 120 deg.C for 12h in a vacuum drying oven.
(4) Cutting: and cutting the round battery negative plate into round battery negative plates with the diameter of 15mm, weighing and placing the round battery negative plates in a drying oven.
(5) Assembling: a CR2025 button cell was assembled in a glove box using a lithium plate as a counter electrode.
LiPF with electrolyte of 1M6DMC (1:1, vol) mixed solution, and the diaphragm is Celgard 2300 polypropylene microporous membrane.
And standing the sealed battery for 24 hours, and performing charge and discharge tests and cycle performance tests on the battery by adopting a Land (blue) battery performance test system. The test results are shown in Table 1.
FIG. 3 is an SEM image of the crystalline/amorphous silicon nanowires prepared in example 1, and it can be seen that the nanowires have a length of 0.1-1 μm and a diameter of 30-50 nm.
FIG. 4 is a TEM image of the crystalline/amorphous silicon nanowire prepared in this example 1, which shows that the diameter of the crystalline silicon core of the nanowire is 5-10 nm, and the thickness of the amorphous silicon layer is 5-20 nm.
FIG. 5 is a TEM image of the crystalline/amorphous silicon-carbon nanowire prepared in example 1, which shows that the diameter of the crystalline silicon core of the nanowire is 5-10 nm, the thickness of the amorphous silicon layer is 5-20 nm, and the thickness of the carbon outer layer is 5-10 nm.
Fig. 6 shows the electrochemical cycling performance test result of a battery assembled by using the crystalline/amorphous silicon-carbon nanowire gradient composite material prepared in this example 1 as the negative electrode material of the battery, wherein the current density is 1.0C, the cycling performance is stable, and after 200 cycles, the specific capacity is 1286mA h g-1。
FIG. 7 is a view of this embodimentExample 1 electrochemical rate performance test results of batteries assembled by using the crystalline/amorphous silicon-carbon nanowire gradient composite material as a negative electrode material of the batteries, wherein the test current densities are 0.2C, 0.5C, 1.0C, 2.0C and 3.0C respectively, and the specific capacities are 2433mA h g h-1、1884mA h g-1、1320mA h g-1、854mA h g-1And 625mA h g-1。
Example 2
Preparation of crystalline/amorphous silicon nanowires:
a10 kW thermal plasma device is adopted to prepare the crystalline/amorphous silicon-carbon nanowires, and the device mainly comprises a 10kW plasma generation system, a feeding system, a graphite inner sleeve-stainless steel shell double-layer regulator, a gas distribution system, a product collection system, a tail gas discharge system and the like. The raw material silicon powder is commercial micron silicon powder with the particle size of 10 mu m. Introducing center gas (argon) into the plasma device, after the plasma arc is formed and stably operates for 3 minutes, adding silicon powder through a feeder, wherein the feeding speed is 10g/min, the carrier gas is argon, and the carrier gas speed is 1.0m3H is used as the reference value. And (3) extinguishing the arc after stopping feeding, and collecting the crystal/amorphous silicon nanowires with the diameter of 10-30 nm and the length of 300 nm.
Preparation of crystalline/amorphous silicon-carbon nanowires:
dissolving 20g of glucose in deionized water, adding 50g of the prepared silicon nanowire under the stirring condition, and stirring and ultrasonically treating to obtain uniformly dispersed suspension; and (3) carrying out spray drying on the turbid liquid to obtain a precursor of the silicon-carbon nanowire, wherein the spray drying conditions are as follows: the inlet temperature was 230 ℃, the outlet temperature was 110 ℃ and the cyclone amount was 100%. And placing the obtained precursor composite material of the silicon-carbon nanowire in a tube furnace, preserving the heat for 10 hours at 500 ℃ in argon atmosphere, and naturally cooling to room temperature to obtain the crystalline/amorphous silicon-carbon nanowire, wherein the silicon content is 76%, the carbon content is 24%, and the carbon layer thickness is 15 nm.
And (3) performance detection:
the crystalline/amorphous silicon-carbon nanowires prepared in this example were used as the negative electrode material of a battery to assemble a battery, and electrochemical performance tests were performed, the results of which are shown in table 1.
Example 3
Preparation of crystalline/amorphous silicon nanowires:
a10 kW thermal plasma device is adopted to prepare the crystalline/amorphous silicon-carbon nanowires, and the device mainly comprises a 10kW plasma generation system, a feeding system, a graphite inner sleeve-stainless steel shell double-layer regulator, a gas distribution system, a product collection system, a tail gas discharge system and the like. The raw material silicon powder is commercially available micron silicon powder with the particle size of 30 microns. Introducing central gas (argon) into the plasma device, after the plasma arc is formed and stably operates for 3 minutes, adding silicon powder through a feeder, wherein the feeding speed is 6g/min, the carrier gas is argon, and the carrier gas speed is 0.8m3H is used as the reference value. And (3) extinguishing the arc after stopping feeding, and collecting the crystal/amorphous silicon nanowires with the diameter of 50-70 nm and the length of 200 nm.
Preparation of crystalline/amorphous silicon-carbon nanowires:
dissolving 100g of sucrose in deionized water, adding 50g of the prepared silicon nanowire under the stirring condition, and stirring and ultrasonically treating to obtain uniformly dispersed suspension; and (3) carrying out spray drying on the turbid liquid to obtain a precursor of the silicon-carbon nanowire, wherein the spray drying conditions are as follows: the inlet temperature was 230 ℃, the outlet temperature was 110 ℃ and the cyclone amount was 100%. And placing the obtained precursor composite material of the silicon-carbon nanowire in a tube furnace, preserving the heat for 2h at 1200 ℃ in argon atmosphere, and naturally cooling to room temperature to obtain the crystalline/amorphous silicon-carbon nanowire, wherein the silicon content is 55%, the carbon content is 45%, and the thickness of the carbon layer is 25 nm.
And (3) performance detection:
the crystalline/amorphous silicon-carbon nanowires prepared in this example were used as the negative electrode material of a battery to assemble a battery, and electrochemical performance tests were performed, the results of which are shown in table 1.
Example 4
Preparation of crystalline/amorphous silicon nanowires:
a30 kW thermal plasma device is adopted to prepare the crystalline/amorphous silicon-carbon nanowires, and the device mainly comprises a 30kW plasma generation system, a feeding system, a graphite inner sleeve-stainless steel shell double-layer regulator, a gas distribution system, a product collection system, a tail gas discharge system and the like. The raw material silicon powder is commercially availableMicron silicon powder with the particle size of 50 microns. Introducing center gas (argon) into the plasma device, after the plasma arc is formed and stably operates for 3 minutes, adding silicon powder through a feeder, wherein the feeding speed is 10g/min, the carrier gas is hydrogen, and the carrier gas speed is 2m3H is used as the reference value. And (3) extinguishing the arc after stopping feeding, and collecting the crystal/amorphous silicon nanowires with the diameter of 40-60 nm and the length of 400 nm.
Preparation of crystalline/amorphous silicon-carbon nanowires:
dissolving 10g of sucrose in deionized water, adding 50g of the prepared silicon nanowire under the stirring condition, and stirring and ultrasonically treating to obtain uniformly dispersed suspension; and (3) carrying out spray drying on the turbid liquid to obtain a precursor of the silicon-carbon nanowire, wherein the spray drying conditions are as follows: the inlet temperature was 230 ℃, the outlet temperature was 110 ℃ and the cyclone amount was 100%. And placing the obtained precursor composite material of the silicon-carbon nanowire in a tube furnace, preserving the heat for 1h at 1400 ℃ in argon atmosphere, and naturally cooling to room temperature to obtain the crystalline/amorphous silicon-carbon nanowire, wherein the silicon content is 95%, the carbon content is 5%, and the carbon layer thickness is 5 nm.
And (3) performance detection:
the crystalline/amorphous silicon-carbon nanowires prepared in this example were used as the negative electrode material of a battery to assemble a battery, and electrochemical performance tests were performed, the results of which are shown in table 1.
Example 5
Preparation of crystalline/amorphous silicon nanowires:
a30 kW thermal plasma device is adopted to prepare the crystalline/amorphous silicon-carbon nanowires, and the device mainly comprises a 30kW plasma generation system, a feeding system, a graphite inner sleeve-stainless steel shell double-layer regulator, a gas distribution system, a product collection system, a tail gas discharge system and the like. The raw material silicon powder is commercially available micron silicon powder with the particle size of 30 microns. Introducing central gas (argon) into the plasma device, after the plasma arc is formed and stably operates for 3 minutes, adding silicon powder through a feeder, wherein the feeding speed is 5g/min, the carrier gas is argon, and the carrier gas speed is 3m3H is used as the reference value. And (3) extinguishing the arc after stopping feeding, and collecting the crystal/amorphous silicon nanowires with the diameter of 70-100 nm and the length of 500 nm.
Preparation of crystalline/amorphous silicon-carbon nanowires:
dissolving 100g of phenolic resin in ethanol, adding 50g of the prepared silicon nanowire under the stirring condition, and stirring for 30 minutes to obtain a silicon-phenolic resin suspension; heating, concentrating and filtering the suspension to obtain a silicon-phenolic resin composite material; and (3) curing the silicon-phenolic resin composite material in an oven at the curing temperature of 300 ℃ for 3 hours. And placing the obtained precursor composite material of the silicon-carbon nanowire in a tube furnace, preserving the heat for 3h at 1000 ℃ in argon atmosphere, and naturally cooling to room temperature to obtain the crystalline/amorphous silicon-carbon nanowire, wherein the silicon content is 36%, the carbon content is 64%, and the thickness of the carbon layer is 40 nm.
And (3) performance detection:
the crystalline/amorphous silicon-carbon nanowires prepared in this example were used as the negative electrode material of a battery to assemble a battery, and electrochemical performance tests were performed, the results of which are shown in table 1.
Example 6
Preparation of crystalline/amorphous silicon nanowires:
a30 kW thermal plasma device is adopted to prepare the crystalline/amorphous silicon-carbon nanowires, and the device mainly comprises a 30kW plasma generation system, a feeding system, a graphite inner sleeve-stainless steel shell double-layer regulator, a gas distribution system, a product collection system, a tail gas discharge system and the like. The raw material silicon powder is commercially available micron silicon powder with the particle size of 100 mu m. Introducing central gas (argon) into the plasma device, after the plasma arc is formed and stably operates for 3 minutes, adding silicon powder through a feeder, wherein the feeding speed is 20g/min, the carrier gas is argon, and the carrier gas speed is 4.0m3H is used as the reference value. And (3) extinguishing the arc after stopping feeding, and collecting the crystal/amorphous silicon nanowires with the diameter of 70-100 nm and the length of 400 nm.
Preparation of crystalline/amorphous silicon-carbon nanowires:
dissolving 50g of epoxy resin in ethanol, adding 50g of the prepared silicon nanowire under the stirring condition, and stirring for 30 minutes to obtain a silicon-epoxy resin suspension; heating, concentrating and filtering the suspension to obtain a silicon-epoxy resin composite material; and (3) curing the silicon-epoxy resin composite material in an oven at the curing temperature of 150 ℃ for 2 hours. And placing the obtained precursor composite material of the silicon-carbon nanowire in a tube furnace, preserving the heat for 5 hours at 1000 ℃ in argon atmosphere, and naturally cooling to room temperature to obtain the crystalline/amorphous silicon-carbon nanowire, wherein the silicon content is 57%, the carbon content is 43%, and the carbon layer thickness is 20 nm.
And (3) performance detection:
the crystalline/amorphous silicon-carbon nanowires prepared in this example were used as the negative electrode material of a battery to assemble a battery, and electrochemical performance tests were performed, the results of which are shown in table 1.
Examples of the invention Current density mA/g First specific capacity mAh/g Coulombic efficiency
Example 1 420 2433 89.6
Example 2 420 1879 89.8
Example 3 420 1552 90.1
Example 4 420 2586 88.5
Example 5 420 853 90.5
Example 6 420 2065 89.5
It should be understood by those skilled in the art that the foregoing is only an embodiment of the present invention, and the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily made by those skilled in the art within the technical scope of the present invention will be within the scope and disclosure of the present invention.

Claims (11)

1. The crystalline/amorphous silicon-carbon nanowire is characterized by comprising a crystalline silicon core, an amorphous silicon layer and a carbon outer layer from inside to outside in sequence, wherein the crystalline silicon and the amorphous silicon form the silicon nanowire, and the carbon layer is coated on the outer surface of the silicon nanowire to jointly form a three-level structure composite material system;
the crystalline/amorphous silicon-carbon nanowire is prepared by the following method, and the method comprises the following steps: preparing crystalline/amorphous silicon nanowires by thermal plasma; and depositing a carbon layer on the surface of the crystalline/amorphous silicon nanowire;
the preparation of the crystalline/amorphous silicon nanowire by the thermal plasma specifically comprises the following steps:
(1) the thermal plasma generating device generates stable thermal plasma;
(2) conveying silicon powder to heat by using argon or hydrogen as carrier gasPlasma region: the particle diameter of the silicon powder is 1-300 μm, the feeding rate is 1-100 g/min, and the carrier gas flow is 0-5m3The silicon powder is gasified and condensed in the thermal plasma area to form a crystalline silicon core;
(3) the crystalline silicon inner core leaves the hot plasma area and enters the plasma shape regulator under the drive of the air flow: amorphous silicon is deposited on the surface of the amorphous silicon film and grows to form a crystalline/amorphous silicon nanowire, and the morphology controller is a graphite inner sleeve-stainless steel outer shell double-layer closed sleeve;
(4) the crystalline/amorphous silicon nanowires enter the product collection system under gas delivery.
2. The crystalline/amorphous silicon-carbon nanowires of claim 1, wherein the crystalline/amorphous silicon is present in the composite material in a mass ratio of between 5% and 95%.
3. The crystalline/amorphous silicon-carbon nanowires of claim 1, wherein the silicon nanowires have a diameter of 10nm to 100nm and the carbon layer has a thickness of 5nm to 50 nm.
4. A method of fabricating crystalline/amorphous silicon-carbon nanowires according to any one of claims 1 to 3, comprising fabricating crystalline/amorphous silicon nanowires by thermal plasma; and depositing a carbon layer on the surface of the crystalline/amorphous silicon nanowire;
the preparation of the crystalline/amorphous silicon nanowire by the thermal plasma specifically comprises the following steps:
(1) the thermal plasma generating device generates stable thermal plasma;
(2) delivering silicon powder to the thermal plasma region by using argon or hydrogen as a carrier gas: the particle diameter of the silicon powder is 1-300 μm, the feeding rate is 1-100 g/min, and the carrier gas flow is 0-5m3The silicon powder is gasified and condensed in the thermal plasma area to form a crystalline silicon core;
(3) the crystalline silicon inner core leaves the hot plasma area and enters the plasma shape regulator under the drive of the air flow: amorphous silicon is deposited on the surface of the amorphous silicon film and grows to form a crystalline/amorphous silicon nanowire, and the morphology controller is a graphite inner sleeve-stainless steel outer shell double-layer closed sleeve;
(4) the crystalline/amorphous silicon nanowires enter the product collection system under gas delivery.
5. The method of claim 4, wherein the feed rate is 5 to 30 g/min.
6. The method of claim 4, wherein the carrier gas flow is 1.0-3m3/h。
7. The method according to claim 4, wherein the graphite inner sleeve in the profile controller in step (3) can strengthen the high temperature zone of the plasma, control the temperature gradient and prolong the deposition time of amorphous silicon in the low temperature zone.
8. The method of claim 4, wherein the carbon layer deposited on the surface of the crystalline/amorphous silicon nanowires is formed by carbon-containing gas chemical vapor deposition or carbon-containing organic matter thermal treatment.
9. The method according to claim 8, wherein the carbon-containing gas is any one or more of methane, ethane, acetylene, ethylene, propane, propylene and propyne; the carbon-containing organic matter is any one or more of glucose, sucrose, fructose, maltose, galactose, lactose, phenolic resin, epoxy resin, naphthalene resin, cellulose resin, resorcinol resin, coal-derived asphalt and petroleum-derived asphalt.
10. The method as claimed in claim 8, wherein the heat treatment temperature is 500-1500 ℃ and the time is 2-24 h.
11. A lithium ion battery, wherein the negative electrode material of the lithium ion battery comprises a crystalline/amorphous silicon-carbon nanowire according to any one of claims 1 to 3.
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