A nanorod silicon-carbon composite material, a preparation method and application thereof

Abstract

The application discloses a kind of nanorod silicon-carbon composite material and its preparation method and application, belong to lithium ion battery technical field.The nanorod silicon-carbon composite material is with carbon, hydrogen, oxygen, silicon and other elements silane or siloxane as precursor, combine the characteristics of high-frequency thermal plasma high temperature transient, realize the rapid pyrolysis and cooling of precursor under reducing atmosphere, obtain the silicon-carbon composite material that nanosilicon is uniformly dispersed and is coated in carbon material.The method process is simple, easy to popularize, reaction product is environmental protection, safe, production process is continuous controllable, can realize macro preparation.The nanorod silicon-carbon composite material obtained by the application has the advantages of small particle size, good silicon dispersity, higher yield and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and relates to preparation of a nanorod silicon-carbon composite material and application thereof to a lithium ion battery negative electrode. BACKGROUND

[0002] Under the social background of comprehensive development of new energy, lithium ion batteries have attracted much attention due to their high energy density, small size, no memory effect and long service life, and are widely used in various portable digital products and electric vehicles. However, due to the limitations of battery material performance, there are still many problems in the current lithium ion batteries, such as short endurance time, long charging time, rapid capacity decay at low temperature and the like. Therefore, it is urgent to develop new high-performance electrode materials with high energy density, high power density and high safety and low cost.

[0003] Silicon material not only has a theoretical specific capacity of up to 3700 mAh / g, but also has a suitable working potential, especially a high natural abundance and a relatively low cost, and is considered to be a strong contender for the next generation of lithium ion battery negative materials. However, the severe volume expansion of silicon material during lithiation / delithiation will cause phenomena such as electrode structure damage, material pulverization and the like, and it is difficult to form a stable SEI film, resulting in rapid capacity decay. The poor conductivity of silicon itself limits the transfer of electric charge, and it is difficult to achieve stable cycling at high current. In view of these problems, researchers have conducted a large number of studies to improve the electrochemical performance of silicon.

[0004] For example, it is reported in ACS Nano, 2012, vol. 6, 1522-1531 that when the diameter of silicon particles is less than 150 nm, silicon will not crack during cycling. It is reported in Nature Nanotechnology, 2008, vol. 3, 31-35 that the electrochemical performance of silicon nanowires, compared with nanoparticles, can better adapt to the stress caused by the volume expansion of silicon. It is reported in Nature Energy, 2016, vol. 1, 1-8 that a carbon-coated nanosilicon composite material is prepared by a CVD method, and the carbon layer effectively inhibits the volume expansion of silicon while improving the conductivity of silicon. It is reported in Inorganic Chemistry Frontiers, 2018, vol. 5, 1463-1469 that a Si / graphite / Cu-CNT quaternary composite material is prepared by a mechanical ball milling method and a copper-catalyzed chemical vapor deposition process, which enhances the connection between silicon and carbon materials and maintains the stability of the electrode structure.

[0005] Patent CN111717921A discloses a method for realizing one-step, large-batch preparation of SiOx Nanowires.

[0006] Patent CN109742372A discloses a method for preparing a silicon-carbon composite material by combining secondary ball milling and heat treatment.

[0007] Patent CN116799169A discloses a method for preparing a silicon-carbon composite material by combining electrospinning, heat treatment and magnetron sputtering. First, a carbon fiber with a porous structure is obtained by electrospinning and heat treatment, then a layer of silicon is deposited on the surface of the fiber by magnetron sputtering, and finally a layer of graphene is coated on the outer layer by chemical vapor deposition to obtain a silicon-carbon composite material.

[0008] Patent CN107768640A discloses a method for preparing a composite material with a three-level structure composed of a crystalline silicon core, an amorphous silicon layer and a carbon outer layer. First, a crystalline / amorphous silicon nanowire is prepared by thermal plasma, and then a carbon shell is further deposited on the nanowire by a carbon-containing gas.

[0009] Patent CN111106338A discloses a method for preparing a silicon / amorphous carbon / graphene lithium ion battery negative electrode material. First, nano-silicon particles are obtained by hydrolysis of tetraethyl orthosilicate and magnesium reduction; then carbon-coated nano-silicon particles are prepared using nano-silicon and glucose as raw materials; finally, the carbon-coated nano-silicon particles and graphene oxide are mixed, freeze-dried and heat-treated to obtain a silicon / amorphous carbon / graphene lithium ion battery negative electrode material.

[0010] It can be seen that nanocrystallization of silicon and its combination with carbon are effective methods for obtaining ideal silicon negative electrode materials. Researchers have made a lot of work around the preparation method, selection of precursor and construction of special structure. One-dimensional materials can better cope with the stress caused by the volume expansion of silicon and provide a fast path for the transmission of electric charge. This special structure is beneficial to improve the stability and electrochemical performance of the electrode structure, and is considered to be an effective way to obtain high-performance lithium ion battery negative electrode. At present, the methods for preparing one-dimensional materials include chemical vapor deposition, electron beam evaporation and metal-assisted chemical etching. However, these preparation methods have the problems of complex preparation process, high equipment requirement, harsh process conditions, serious pollution and difficulty in large-scale production.

[0011] Therefore, how to simply and massively prepare one-dimensional silicon-carbon composite materials by one-step method is still a great challenge. SUMMARY

[0012] The present application aims to provide a nanorod silicon-carbon composite material in which nanosilicon is uniformly dispersed and coated in carbon material. This structure is conducive to realizing in-situ confinement of nanosilicon and avoiding agglomeration problems that may exist in the cycle process. The excellent conductivity of the carbon material provides an effective path for electron transfer of silicon, promotes the progress of electrochemical reactions, and the tough carbon layer can effectively alleviate or inhibit the volume expansion of silicon in the cycle process. The unique one-dimensional structure is also conducive to enhancing the electrochemical performance of the material. Another object of the present application is to provide a method for preparing the above material by high-frequency thermal plasma.

[0013] To achieve the above object, the present application adopts the following technical solutions.

[0014] A nanorod silicon-carbon composite material, using silane or siloxane containing carbon, hydrogen, oxygen and silicon as main elements as a precursor, combining the characteristics of high-frequency thermal plasma high temperature and transience, realizing rapid pyrolysis and cooling of the precursor in a reducing atmosphere, uniformly dispersing and coating nanosilicon in carbon material, and avoiding the formation of silicon carbide byproducts by reducing atmosphere and rapid cooling speed.

[0015] Further, the silicon-carbon composite material is in the form of nanorods, with a diameter of 1-50 nm and a length of 50 nm-1 μm.

[0016] Further, the silicon content in the silicon-carbon composite material is 10-90wt%.

[0017] The preparation method of the above nanorod silicon-carbon composite material comprises the following steps:

[0018] 1) Ignite argon gas to generate a stable thermal plasma arc using an electric spark generator;

[0019] 2) Introduce hydrogen gas from the quenching gas port or the side gas port to maintain a reducing atmosphere:

[0020] 3) Deliver the silane or siloxane precursor into the plasma arc through a peristaltic pump;

[0021] 4) The silane or siloxane rapidly pyrolyzes in the high-temperature plasma arc and enters the cooling zone;

[0022] 5) The final product enters the product collection system under the action of the quenching gas.

[0023] Further, the power of the high-frequency thermal plasma device in step 1) is 10-200 kw.

[0024] Further, a fine hole is added in the high-frequency plasma gun in step 1), and a carrier gas is added in front of the feed port to improve the gas atomization ability of the liquid phase raw material entering the plasma.

[0025] Further, the flow rate of hydrogen in step 2) is 0-1.0 m 3 / h.

[0026] Further, the precursor in step 3) is a silane or siloxane (mainly containing carbon, hydrogen, oxygen, silicon and other elements, and a compound having Si-O-Si bond) material including trimethylphenylsilane, trimethylsilylmethane, tetraethyl orthosilicate, triethoxyphenylsilane, allyloxytrimethylsilane and the like.

[0027] Further, the feeding amount of the precursor in step 3) is 0.1-2.0 mL / min per kilowatt of plasma power.

[0028] The application also provides application of the above nanorod silicon-carbon composite material in lithium ion batteries.

[0029] Compared with the prior art, the application has the following advantages:

[0030] 1. The high-frequency thermal plasma technology is used to prepare the silicon-carbon composite material by pyrolysis of liquid-phase silane or siloxane as the precursor in one step. The production method is simple, easy to expand, continuous in reaction process and easy to popularize and realize industrial application.

[0031] 2. The precursor used only contains main elements of carbon, hydrogen, oxygen and silicon, and no harmful substances are generated in the pyrolysis process compared with chlorosilane, so that the tail gas does not need further treatment and the process is environmentally friendly and pollution-free.

[0032] 3. The reaction atmosphere and conditions are controllable, and there is no electrode pollution. Under the reducing atmosphere and fast cooling conditions, the generation of by-product silicon carbide is avoided.

[0033] 4. In the prepared nanorod silicon-carbon composite material, the nanosilicon is uniformly dispersed and coated in the carbon material. This structure is beneficial to realize in-situ confinement of the nanosilicon and avoid the possible agglomeration problem in the cycle process. The excellent conductivity of the carbon material can promote the electrochemical reaction, and the tough carbon layer can effectively alleviate or inhibit the volume expansion of silicon in the cycle process. The unique one-dimensional structure provides a fast path for the transfer of electric charges. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 A scanning electron microscope (SEM) photo of the silicon-carbon composite material obtained in Example 1.

[0035] Figure 2 An X-ray diffraction (XRD) chart of the silicon-carbon composite material obtained in Example 1 and Comparative Example 1.

[0036] Figure 3 A thermogravimetric analysis (TGA) curve of the silicon-carbon composite material obtained in Example 6.

[0037] Figure 4 Constant current charge-discharge curves of the silicon-carbon composite material obtained in Example 1 and Comparative Example 1.

[0038] Figure 5 Cycle performance curve of the silicon-carbon composite material obtained in Example 1. DETAILED DESCRIPTION

[0039] The technical solutions of the present application will be described clearly and completely in combination with the drawings of the specification. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application. In the following examples, the experimental methods are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified. Example 1

[0040] A 30 kW high-frequency thermal plasma system was used, which mainly included a gas control system, a thermal plasma generation system, a feeding system, a product collection system, and a tail gas treatment system, etc. After opening the negative pressure, argon was introduced into the plasma, and a plasma arc was formed by using an electric spark generator to break the argon. After stable operation for 5 minutes, hydrogen was introduced from the quenching gas port, and the hydrogen flow rate was 0.5 m 3 / h. The peristaltic pump was opened to add tetraethyl orthosilicate into the plasma system, and the rotation speed was 1.5 rpm, and the feeding rate was about 5 mL / min. After stopping feeding, the hydrogen was turned off, and the arc was extinguished, and the silicon-carbon composite material was collected.

[0041] Characterization of the silicon-carbon composite material:

[0042] The morphology of the silicon-carbon composite material obtained under the above conditions was observed by a Japanese electron scanning microscope (JSM-7001F), as shown in FIG. 1: the obtained material was nanorod-shaped. Figure 1

[0043] The phase composition of the silicon-carbon composite material prepared under the above conditions was analyzed by an X-ray powder diffractometer (X' Pert PRO MPD). As shown in FIG. 2: the material was mainly composed of crystalline silicon (JCPDS: 00-027-1402) and amorphous carbon (dough peak at about 24°). Figure 2

[0044] The content of silicon in the silicon-carbon composite material obtained under the above conditions was tested by a simultaneous thermal gravimetric analyzer (NETZSCH STA 449F3).

[0045] Electrochemical performance characterization of the silicon-carbon composite material: ​​

[0046] The prepared silicon-carbon composite material, Super P (conductive agent), sodium carboxymethyl cellulose (binder) were mixed in a mass ratio of 8:1:1 with deionized water as the solvent to form a slurry, which was uniformly coated on a copper foil current collector to obtain an electrode sheet. A metal lithium was used as the counter electrode, a polypropylene microporous membrane was used as the separator, and 1 mol / L LiPF6 (the solvent was a mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1, containing 10% fluoroethylene carbonate) was used as the electrolyte. A button cell was assembled in an argon glove box, and charge-discharge test was performed. The test current density was 100 mA / g, and the charge-discharge voltage interval was 0.01-3.0 V. The battery test results are listed in Table 1, Figure 4 and Figure 5 . Example 2

[0047] A 30 kW high-frequency thermal plasma system was used, which mainly included a gas control system, a thermal plasma generation system, a feeding system, a product collection system, and a tail gas treatment system. The negative pressure was opened, argon was introduced into the plasma, and a plasma arc was formed by using an electric spark generator to break the argon. After stable operation for 5 minutes, hydrogen was introduced from the quenching gas port, and the hydrogen flow rate was 1.0 m 3 / h. The peristaltic pump was opened to add tetraethyl orthosilicate into the plasma system, and the rotation speed was 1.5 rpm. The feeding rate was about 5 mL / min. After stopping feeding, the hydrogen was closed, the arc was extinguished, and the silicon-carbon composite material was collected.

[0048] The physical characterization of the silicon-carbon composite material was the same as in Example 1.

[0049] The battery assembly and performance characterization were the same as in Example 1. The battery test results of the obtained silicon-carbon composite material are listed in Table 1. Example 3

[0050] A 30 kW high-frequency thermal plasma system was used, which mainly included a gas control system, a thermal plasma generation system, a feeding system, a product collection system, and a tail gas treatment system. The negative pressure was opened, argon was introduced into the plasma, and a plasma arc was formed by using an electric spark generator to break the argon. After stable operation for 5 minutes, hydrogen was introduced from the quenching gas port, and the hydrogen flow rate was 1.0 m 3 / h. The peristaltic pump was opened to add tetraethyl orthosilicate into the plasma system, and the rotation speed was 1.5 rpm. The feeding rate was about 5 mL / min. After stopping feeding, the hydrogen was closed, the arc was extinguished, and the silicon-carbon composite material was collected.

[0051] The physical characterization of the silicon-carbon composite material was the same as in Example 1.

[0052] The battery assembly and performance characterization were the same as in Example 1. The battery test results of the obtained silicon-carbon composite material are listed in Table 1. Example 4

[0053] A 30 kW high frequency thermal plasma system was used, which mainly contains gas control system, thermal plasma generation system, feeding system, product collection system and tail gas treatment system, etc. Open the negative pressure, pass argon into the plasma, use the spark generator to break the argon to form plasma arc. After stable operation for 5 minutes, pass hydrogen into the quenching gas port, the hydrogen flow rate is 0.5 m 3 / h. Open the peristaltic pump to add trimethylsilylmethane into the plasma system, the rotation speed is 1.5 rpm, the feeding rate is about 5 mL / min. After stopping feeding, close the hydrogen, extinguish the arc, and collect the silicon-carbon composite material.

[0054] The physical characterization of the silicon-carbon composite material is the same as that of Example 1.

[0055] The assembly and performance characterization of the battery are the same as those of Example 1. The battery test results of the obtained silicon-carbon composite material are listed in Table 1. Example 5

[0056] A 30 kW high frequency thermal plasma system was used, which mainly contains gas control system, thermal plasma generation system, feeding system, product collection system and tail gas treatment system, etc. Open the negative pressure, pass argon into the plasma, use the spark generator to break the argon to form plasma arc. After stable operation for 5 minutes, pass hydrogen into the quenching gas port, the hydrogen flow rate is 0.5 m 3 / h. Open the peristaltic pump to add trimethylsilylmethane into the plasma system, the rotation speed is 1.5 rpm, the feeding rate is about 5 mL / min. After stopping feeding, close the hydrogen, extinguish the arc, and collect the silicon-carbon composite material.

[0057] The physical characterization of the silicon-carbon composite material is the same as that of Example 1.

[0058] The assembly and performance characterization of the battery are the same as those of Example 1. The battery test results of the obtained silicon-carbon composite material are listed in Table 1. Example 6

[0059] A 100 kW high frequency thermal plasma system was used, which mainly contains gas control system, thermal plasma generation system, feeding system, product collection system and tail gas treatment system, etc. Open the negative pressure, pass argon into the plasma, use the spark generator to break the argon to form plasma arc. After stable operation for 5 minutes, pass hydrogen into the quenching gas port, the hydrogen flow rate is 0.5 m 3 / h. Open the peristaltic pump to add trimethylsilylmethane into the plasma system, the rotation speed is 1.5 rpm, the feeding rate is about 5 mL / min. After stopping feeding, close the hydrogen, extinguish the arc, and collect the silicon-carbon composite material.

[0060] The physical characterization of the silicon-carbon composite material was the same as that of Example 1.

[0061] The results of the thermogravimetric analysis are shown in Figure 3 .

[0062] The assembly of the battery and the performance characterization were the same as those of Example 1. The battery test results of the obtained silicon-carbon composite material are listed in Table 1.

[0063] Comparative Example 1

[0064] A 30 kW high-frequency thermal plasma system was used, which mainly included a gas control system, a thermal plasma generation system, a feeding system, a product collection system, and a tail gas treatment system. After opening the negative pressure, argon was introduced into the plasma, and a plasma arc was formed by using an electric spark generator to break the argon. After stable operation for 5 minutes, a peristaltic pump was opened to add tetraethyl orthosilicate into the plasma system, and the rotation speed was 1.5 rpm, and the feeding rate was about 5 mL / min. After stopping feeding, the hydrogen was closed, the arc was extinguished, and the silicon-carbon composite material was collected.

[0065] The physical characterization of the silicon-carbon composite material was the same as that of Example 1.

[0066] The XRD characterization is shown in Figure 2 , and in addition to crystalline silicon and amorphous carbon in the product, diffraction peaks of silicon carbide and graphite carbon also appeared, and the diffraction peak intensity of silicon carbide was similar to that of crystalline silicon, which might affect the electrochemical performance of the material.

[0067] The assembly of the battery and the performance characterization were the same as those of Example 1. The battery test results of the obtained silicon-carbon composite material are listed in Table 1 and Figure 4 .

[0068] Table 1 Battery performance test results

[0069]

[0070] As can be seen from Examples 1-3, the hydrogen flow rate was 0.5-1.0 m 3The hydrogen content between 0 and 1.5 wt% and the hydrogen addition by quenching gas or edge gas port have little effect on the electrochemical performance of the obtained silicon-carbon composite material. As can be seen from Examples 4 and 5, the different silicon content in the precursor has an effect on the silicon content in the silicon-carbon composite material obtained after pyrolysis. As can be seen from Example 6, increasing the power of the thermal plasma can achieve a greater feed amount, and the electrochemical performance has little effect compared with the silicon-carbon composite material obtained under small power conditions. As can be seen from Comparative Example 1, the silicon-carbon composite material obtained under argon conditions, although the thermogravimetry indicates that the residual mass is 80%, but through XRD it can be known that more silicon carbide by-products are generated under this condition, resulting in a lower actual capacity. Therefore, the selection of suitable atmosphere conditions and precursors has a great influence on the performance of the final silicon-carbon composite material.

[0071] Although the embodiments of the present application have been shown and described above, it should be understood by those skilled in the art that the above embodiments are exemplary and cannot be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments without departing from the principles and spirit of the present application within the scope of the present application. The scope of protection of the present application is defined by the claims and their equivalent technical solutions.

Claims

1. A nanorod silicon-carbon composite material, characterized by, The silicon or siloxane is used as a precursor, and under the action of high-frequency thermal plasma high temperature transient, the precursor is rapidly pyrolyzed and cooled, so that silicon is dispersed in carbon material in nanometer scale, and a silicon-carbon composite material is obtained.

2. The silicon-carbon composite material of claim 1, wherein, The prepared silicon-carbon composite material is in the form of nanorod, with a diameter of 1-50 nm and a length of 50 nm-1 μm.

3. The silicon-carbon composite of claim 1, wherein, The mass percentage of silicon in the prepared silicon-carbon composite material is 10-90%.

4. The preparation method of the silicon-carbon composite material according to any one of claims 1-3, comprising the following steps: 1) igniting argon to generate a stable thermal plasma arc by using an electric spark generator; 2) introducing hydrogen from a quenching gas port or a side gas port to maintain a reducing atmosphere; 3) feeding the silane or siloxane precursor into the plasma arc by using a peristaltic pump; 4) the silane or siloxane is rapidly pyrolyzed in the high-temperature plasma arc and then enters the cooling zone; 5) the final product enters the product collection system under the action of the quenching gas.

5. The production method according to claim 4, characterized by The power of the high-frequency thermal plasma device in step 1) is 10-200 kw.

6. The preparation method according to claim 4, characterized in that, In step 1), a fine hole is added in the high-frequency plasma gun, and a carrier gas is added in front of the feeding port to improve the gas atomization ability of the liquid raw material entering the plasma.

7. The production method according to claim 4, characterized by, The flow rate of hydrogen gas in step 2) is 0 to 1.0 m 3 / h.

8. The preparation method according to claim 4, characterized in that, The precursor in step 3) is a silane or siloxane material including trimethylphenylsilane, trimethylsilylmethane, tetraethyl silicate, triethoxyphenylsilane, and allyloxytrimethylsilane.

9. The production method according to claim 4, characterized by, The feeding amount of the precursor in step 3) is 0.1-2.0 mL / min per kilowatt of plasma power.

10. A lithium-ion battery, characterized by, The negative electrode material of the lithium ion battery comprises the silicon-carbon composite material according to any one of claims 1-3.

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