Nanosilicon, method for preparing the same and lithium-ion battery anode material

Abstract

The application provides nano silicon, a preparation method thereof and a lithium ion battery negative electrode material. The method for preparing the nano silicon comprises the following steps: S100, feeding mixed gas into a preheater to preheat the mixed gas to a preheating temperature, wherein the mixed gas comprises a reaction silicon-based gas and a carrier gas; S200, feeding the preheated mixed gas into a gas phase reactor through a first gas inlet of the gas phase reactor to perform a gas phase deposition reaction, so as to obtain a gas-powder mixed product, wherein the temperature of the gas phase deposition reaction is greater than the preheating temperature; and S300, cooling and separating the gas-powder mixed product, so as to obtain the nano silicon and tail gas, wherein the average particle size of the nano silicon is less than or equal to 100 nm, and the steps S100, S200 and S300 are all performed under the protection of inert gas. The nano silicon with a particle size less than or equal to 100 nm can be obtained by the above-mentioned method, and the above-mentioned steps are all completed under the protection of inert gas, so that the nano silicon with high purity can be obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of materials, in particular, to nano-silicon, a preparation method thereof and a lithium ion battery negative electrode material. BACKGROUND

[0002] Since silicon can be alloyed with lithium at room temperature to form Li4Si alloy phase, the theoretical specific capacity is as high as 4200 mAh / g, and therefore, silicon negative electrode material has attracted much attention from researchers and is considered to be one of the most potential negative electrode materials for the next generation of lithium ion batteries. However, in the repeated process of lithium extraction / insertion, the inherent low conductivity and excessive volume change of silicon hinder the practical application of silicon in lithium ion batteries in the commercial field. In order to solve the above-mentioned difficulties, preparing nano-silicon material with a particle size of less than 150 nm is an effective method to improve the performance of lithium ion batteries. The quality of nano-silicon products on the market is uneven, and the cost difference is also large, which is due to the high requirements of silicon nanocrystallization on raw materials, equipment and process conditions. For example, in the preparation of zero-dimensional nanoparticles, the cost of plasma method is high, and it is difficult to scale up production; the silane pyrolysis method still has technical problems in particle controllable deposition and continuous stable operation of equipment; the magnesium thermal reduction method has relatively poor consistency in particle size and control of product purity, which needs to be further improved; in the grinding process, the powder agglomeration phenomenon is serious, and after the particle size reaches a certain size, it is difficult to continue to decrease, and the newly prepared powder is seriously oxidized. SUMMARY

[0003] The present application aims to at least solve one of the technical problems in the related art. To this end, one object of the present application is to provide a method for preparing nano-silicon, by which nano-silicon with a particle size of less than or equal to 100 nm or high purity can be prepared.

[0004] In one aspect of the present application, the present application provides a method for preparing nano-silicon. According to an embodiment of the present application, the method for preparing nano-silicon comprises: S100: passing a mixed gas into a preheater to preheat to a preheating temperature, wherein the mixed gas comprises a reaction silicon-based gas and a carrier gas; S200: passing the preheated mixed gas into a gas phase reactor through a first gas inlet of the gas phase reactor to carry out a gas phase deposition reaction, to obtain a gas-powder mixed product, and the temperature of the gas phase deposition reaction is greater than the preheating temperature; S300: cooling and separating the gas-powder mixed product to obtain nano-silicon and tail gas, and the average particle size of the nano-silicon is less than or equal to 100 nm, wherein steps S100, S200 and S300 are all carried out under the protection of inert gas. Thus, by the above-mentioned method of gas phase deposition for preparing nano-silicon, nano-silicon with a particle size of less than or equal to 100 nm can be obtained, and the above-mentioned steps are all completed under the protection of inert gas, which is further helpful to obtain nano-silicon with high purity.

[0005] According to an embodiment of the present application, the method for preparing nano-silicon further comprises: during the gas phase deposition reaction, introducing the carrier gas into the gas phase reactor through a second gas inlet of the gas phase reactor.

[0006] According to an embodiment of the present application, the reactive silicon-based gas is at least one of dichlorosilane, trichlorosilane, monosilane and disilane, and the carrier gas is one of hydrogen, argon and nitrogen.

[0007] According to an embodiment of the present application, the preheating temperature is 80-600°C, and the temperature of the gas phase deposition reaction is 200-1200°C.

[0008] According to an embodiment of the present application, the pressure of the gas phase deposition reaction is 0-0.5 MPa.

[0009] According to an embodiment of the present application, the molar concentration of the reactive silicon-based gas in the gas phase reactor is 40-80 mol%.

[0010] According to an embodiment of the present application, the average particle size of the nano-silicon is 30-100 nm.

[0011] According to an embodiment of the present application, the separation is achieved by trapping the nano-silicon in a trap, which is an electrostatic trap or a bag-type trap.

[0012] According to an embodiment of the present application, the method for preparing nano-silicon further comprises: after filtering the tail gas, introducing the tail gas into a tail gas treatment device, wherein the filtering is achieved by using a bag-type dust collector, an inorganic filter membrane or an organic filter membrane.

[0013] In another aspect of the present application, the present application provides a nano-silicon. According to an embodiment of the present application, the nano-silicon is prepared by the method described above, the average particle size of the nano-silicon is less than or equal to 100 nm, and the surface oxygen content of the nano-silicon is less than or equal to 1.0 wt%. Thus, the nano-silicon has a small particle size and high purity, and has a good structure and electrochemical stability. When the nano-silicon is used to prepare a negative electrode of a lithium ion battery, the performance of the negative electrode and the lithium ion battery can be greatly improved.

[0014] In still another aspect of the present application, the present application provides a lithium ion battery negative electrode material. According to an embodiment of the present application, the lithium ion battery negative electrode material comprises the nano-silicon described above. Since the nano-silicon has a small particle size and high purity, when it is used as a negative electrode material, the stress change of Li-Si alloying during the charging and discharging process and the pulverization of silicon particles can be effectively alleviated, and the structure and electrochemical stability of silicon can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0015] The above and / or additional aspects and advantages of the present application will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the references to the following drawings:

[0016] Figure 1 is a flow chart of preparing nano-silicon in one embodiment of the present application. DETAILED DESCRIPTION

[0017] The scheme of the present application will be explained below with reference to the examples. Those skilled in the art will appreciate that the following examples are intended to be illustrative only and should not be viewed as limiting the scope of the present application. Unless otherwise indicated, in the examples, the techniques and conditions described in the literature or according to the product manual are used. Unless otherwise indicated, the reagents or instruments used are commercially available conventional products.

[0018] The present application will be described with respect to the following examples. It is to be understood that the examples are merely illustrative of the present application and should not be viewed as limiting the scope of the present application.

[0019] In one aspect of the present application, the present application provides a method for preparing nano-silicon. According to an embodiment of the present application, with reference to Figure 1 , the method for preparing nano-silicon comprises:

[0020] S100: passing a mixed gas into a preheater to preheat to a preheating temperature, the mixed gas comprising a reaction silicon-based gas and a carrier gas. Thus, the mixed gas is heated to a certain temperature in advance before the vapor deposition is performed, which can reduce the occurrence of side reactions in the gas phase reactor on the one hand, and can reduce the reaction rate on the other hand, so that the mixed gas quickly reaches the reaction temperature in the gas phase reactor.

[0021] According to an embodiment of the present application, the reaction silicon-based gas is at least one of dichlorodihydrogen silicon, trichlorohydrogen silicon, monosilane and disilane, and the carrier gas is one of hydrogen, argon and nitrogen. Thus, the above reaction silicon-based gas can effectively generate silicon powder through the vapor deposition reaction, and the carrier can protect the silicon powder from being oxidized on the one hand, and can ensure the stable progress of the vapor deposition reaction on the other hand, adjust the concentration of the reaction silicon-based gas, and ensure a good reaction rate and yield.

[0022] According to an embodiment of the present application, the above preheating temperature is 80℃-600℃, such as 80℃, 100℃, 150℃, 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃.

[0023] The specific type of the preheater is not particularly required, and a person skilled in the art can flexibly select according to the actual situation. In some embodiments, the preheater can be one of a plate type preheater, a tube type preheater and a rotary type preheater, so that the mixed gas can be uniformly preheated and the temperature can be controlled.

[0024] S200: passing the preheated mixed gas into the gas phase reactor through the first gas inlet of the gas phase reactor to perform a gas phase deposition reaction, to obtain a gas-powder mixed product, and the temperature of the gas phase deposition reaction is greater than the preheating temperature. It should be noted that during the gas phase deposition reaction, the preheated mixed gas is continuously passed into the gas phase reactor to ensure the continuous progress of the reaction.

[0025] In the above step, through the gas phase deposition reaction, the reaction silicon-based gas is thermally decomposed to obtain silicon powder, and the gas-powder mixed product includes powder and gas. The powder is the silicon powder obtained by the gas phase deposition reaction, and the gas includes the original carrier gas and hydrogen generated by the gas phase deposition reaction. When silane and trichlorosilane are used as raw materials, the principle of the gas phase deposition reaction is: SiH4=Si+2H2↑, 4SiHCl3=Si+3SiCl4+2H2↑.

[0026] Further, the temperature of the gas phase deposition reaction is 200℃-1200℃, such as 200℃, 300℃, 400℃, 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃, 1200℃. At the above reaction temperature, the gas phase deposition reaction can be smoothly carried out at a better reaction rate, and the specific temperature can be flexibly set according to the actual situation of the selected reaction silicon-based gas and the requirement of the reaction rate.

[0027] According to the embodiments of the present application, the pressure of the gas phase deposition reaction is 0-0.5MPa, such as 0.5MPa, 0.4MPa, 0.3MPa, 0.2MPa, 0.1MPa, 0.05MPa, etc. In this way, it is beneficial for the gas phase deposition reaction to be smoothly carried out at a better reaction rate. It should be noted that the pressure of the gas phase deposition reaction is greater than 0.

[0028] According to the embodiments of the present application, based on all the gas in the gas phase reactor, the molar concentration of the reaction silicon-based gas in the gas phase reactor is 40mol%-80mol%, such as 40mol%, 45mol%, 50mol%, 55mol%, 60mol%, 65mol%, 70mol%, 75mol%, 80mol%. The above concentration of the reaction silicon-based gas can smoothly carry out the gas phase deposition reaction, and ensure a better reaction rate.

[0029] According to the embodiment of the present application, the method for preparing nanometer silicon further comprises: during the gas phase deposition reaction, feeding a carrier gas into the gas phase reactor through the second gas inlet of the gas phase reactor. In this way, during the reaction, the carrier gas is fed into the gas phase reactor through the second gas inlet of the reactor, so that the concentration of the reaction silicon-based gas and the temperature of the mixed gas in the reactor can be adjusted in real time during the gas phase deposition reaction, so as to meet the optimal reaction silicon-based gas concentration and reaction temperature described above, so as to ensure the stable progress of the gas phase deposition reaction; in addition, through the above adjustment, the particle size of the nanometer silicon can be effectively fine-tuned. The carrier gas fed in this step needs to be further preheated, and the preheating temperature can be greater than the preheating temperature of the mixed gas and less than or equal to the temperature of the gas phase deposition reaction.

[0030] Further, the specific structure of the gas phase reactor has no special requirements, and those skilled in the art can flexibly design the specific structure of the gas phase reactor according to the various requirements of the above-mentioned gas phase deposition reaction and the like. In some specific embodiments, the reactor can realize intelligent monitoring of reaction temperature, reaction pressure, gas inlet flow and other parameters, the first gas inlet, the second gas inlet, the gas outlet and the feeding port are finely designed, the layout is reasonable, the reaction zone temperature is stable and controllable, the nanometer silicon reaction rate can be accurately controlled, the nanometer silicon grown to a certain size is timely discharged, and continuous growth is avoided.

[0031] S300: cooling and separating the gas-powder mixed product to obtain nanometer silicon and tail gas, the average particle size of the nanometer silicon being less than or equal to 100 nm, wherein steps S100, S200 and S300 are all carried out under the protection of inert gas (such as argon, nitrogen, etc.). Through the protection of inert gas, the oxygen content on the surface of the nanometer silicon can be greatly reduced.

[0032] According to the embodiment of the present application, the separation of the gas-powder mixed product is completed by trapping the nanometer silicon with a trap, and the nanometer silicon is trapped into a material collecting tank by using the trap, which is an electrostatic trap or a bag trap. The above classification method is simple and easy to operate, and has better separation effect, which can separate the nanometer silicon powder from the gas to the greatest extent.

[0033] According to the embodiment of the present application, the nanometer silicon powder obtained after separation can be further vacuum packaged to avoid contact with oxygen and pollution.

[0034] According to the embodiments of the present application, the separation method is difficult to separate the nanometer silicon powder from the gas completely, so there is still a small amount of powder in the tail gas. Therefore, in some embodiments, the method for preparing nanometer silicon can further include filtering the tail gas to filter out the powder in the tail gas, and then introducing the filtered tail gas into a tail gas treatment device. Further, the filtering can use a bag dust collector, an inorganic filter membrane or an organic filter membrane, so that the filtering effect is better and the process method is simple and easy to implement.

[0035] According to the embodiments of the present application, the nanometer silicon is prepared by the above-mentioned vapor deposition method, the whole reaction process is controlled in a fine way and is completed under the protection of inert gas, so that the nanometer silicon with a particle size of less than or equal to 100 nm, low oxygen content and high purity can be obtained. In some embodiments, the prepared nanometer silicon is used as a negative material of a lithium ion battery after being compounded with carbon, the first coulomb efficiency is greatly improved, and the cycle performance and fast charging performance of the battery are greatly improved. In summary, the method for preparing nanometer silicon of the present application considers and designs the raw materials, equipment, process and parameters as a whole, the whole process is protected by gas, the powder particle size is fine, the oxygen content is low, the purity is high, the problem of low first coulomb efficiency of silicon-based negative material caused by surface oxidation of nanometer silicon is greatly improved, and high-purity nanometer silicon powder can be prepared on a large scale at low cost. The silicon-based negative material prepared by using the high-purity nanometer silicon of the present application has higher first coulomb efficiency, higher purity, and at the same time has the characteristics of high specific capacity, good high cycle stability and high safety of general silicon-based negative materials.

[0036] Further, the average particle size of the nanometer silicon is 30 nm to 100 nm, such as 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm, and the surface oxygen content of the nanometer silicon is less than or equal to 1.0 wt%.

[0037] In another aspect of the present application, the present application provides a nanometer silicon. According to the embodiments of the present application, the nanometer silicon is prepared by the method described above, the average particle size of the nanometer silicon is less than or equal to 100 nm, and the surface oxygen content of the nanometer silicon is less than or equal to 1.0 wt%. Therefore, the nanometer silicon has a small particle size, high purity, and good structure and electrochemical stability. When the nanometer silicon is compounded with carbon and used as a negative material of a lithium ion battery, the first coulomb efficiency is greatly improved, the cycle performance and fast charging performance of the battery are greatly improved, and the overall performance of the lithium ion battery is further improved.

[0038] In yet another aspect of the present application, the present application provides a lithium ion battery negative electrode material. According to an embodiment of the present application, the lithium ion battery negative electrode material comprises the nano-silicon as described above. Due to the small particle size and high purity of the nano-silicon, the nano-silicon as the negative electrode material can effectively relieve the stress change of Li-Si alloying in the charging and discharging process and inhibit the pulverization of silicon particles, greatly improve the first coulombic efficiency, greatly improve the cycle performance and fast charging performance of the battery, and further improve the overall performance of the lithium ion battery.

[0039] Embodiment

[0040] Embodiment 1

[0041] The gas phase preparation method of high-purity nano-silicon specifically comprises the following steps:

[0042] The trichlorosilane is mixed with hydrogen (the molar concentration of the trichlorosilane is 40 mol%) to form a mixed gas, the mixed gas is preheated to 600°C by a plate preheater, and then is introduced into a gas phase reactor through a first gas inlet for a gas phase deposition reaction, and the temperature of the gas phase deposition reaction is 1100°C;

[0043] Another carrier gas (hydrogen) is preheated to 800°C, and according to the reaction condition in the gas phase reactor, the concentration and temperature of the trichlorosilane in the reactor are fine-tuned by adjusting the gas inlet amount and temperature, so that the concentration of the trichlorosilane is about 40 mol% and the reaction temperature is about 1100°C, thereby adjusting the reaction rate and controlling the particle size of the nano-silicon;

[0044] The generated gas-powder mixed product is cooled to 25°C by a cooler, and then is subjected to gas-powder separation, the finished nano-silicon powder is captured by an electrostatic precipitator, and is vacuum packaged; the reaction tail gas is filtered by a bag-type dust collector and then is subjected to tail gas treatment.

[0045] Test analysis: The average particle size of the high-purity nano-silicon is 35 nm by random testing, and the surface oxygen content is 0.97 wt%.

[0046] Embodiment 2

[0047] The gas phase preparation method of high-purity nano-silicon specifically comprises the following steps:

[0048] The silane is mixed with argon (the molar concentration of the silane is 60 mol%) to form a mixed gas, the mixed gas is preheated to 250°C by a plate preheater, and then is introduced into a gas phase reactor through a first gas inlet for a gas phase deposition reaction, and the temperature of the gas phase deposition reaction is 600°C;

[0049] The other carrier gas (argon) is preheated to 500℃, and according to the reaction in the gas phase reactor, the concentration and temperature of trichlorosilane in the reactor are fine-tuned by adjusting the gas inlet amount and temperature, so that the concentration of silane is about 60mol%, the reaction temperature is about 600℃, and the reaction rate is adjusted to control the particle size of nanosilicon.

[0050] The generated gas-powder mixed product is cooled to 25℃ by a cooler, and then gas-powder separation is performed, the finished nanosilicon powder is captured by an electrostatic precipitator, and vacuum packaging is performed; the reaction tail gas is filtered by a bag dust collector and then tail gas treatment is performed.

[0051] Test analysis: the average particle size of high-purity nanosilicon is 54nm by random testing, and the surface oxygen content is 0.32wt%.

[0052] Example 3

[0053] The gas phase preparation method of high-purity nanosilicon specifically includes the following steps:

[0054] Dichlorosilane is mixed with hydrogen (the molar concentration of trichlorosilane is 80mol%) to form a mixed gas, the mixed gas is preheated to 80℃ by a plate preheater, and then introduced into a gas phase reactor through a first gas inlet for gas phase deposition reaction, and the temperature of the gas phase deposition reaction is 200℃;

[0055] The other carrier gas (hydrogen) is preheated to 200℃, and according to the reaction in the gas phase reactor, the concentration and temperature of dichlorosilane in the reactor are fine-tuned by adjusting the gas inlet amount and temperature, so that the concentration of trichlorosilane is about 80mol%, the reaction temperature is about 200℃, and the reaction rate is adjusted to control the particle size of nanosilicon.

[0056] The generated gas-powder mixed product is cooled to 25℃ by a cooler, and then gas-powder separation is performed, the finished nanosilicon powder is captured by an electrostatic precipitator, and vacuum packaging is performed; the reaction tail gas is filtered by a bag dust collector and then tail gas treatment is performed.

[0057] Test analysis: the average particle size of high-purity nanosilicon is 96nm by random testing, and the surface oxygen content is 0.58wt%.

[0058] The terms "first", "second", etc. are used only for the purpose of description and should not be understood as indicating or implying relative importance or implying the number of the technical features indicated. Therefore, the features defined as "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise specifically limited.

[0059] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are contained in at least one embodiment or example of the present application. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0060] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

Claims

1. A method for producing nanosilicon, characterized by, The method comprises the following steps: S100: passing a mixed gas into a preheater to preheat the mixed gas to a preheating temperature, wherein the mixed gas comprises a reaction silicon-based gas and a carrier gas; S200: passing the preheated mixed gas into a gas-phase reactor through a first gas inlet of the gas-phase reactor to perform a gas-phase deposition reaction, to obtain a gas-powder mixed product, wherein the temperature of the gas-phase deposition reaction is greater than the preheating temperature; S300: cooling and separating the gas-powder mixed product to obtain the nano-silicon and tail gas, wherein the average particle size of the nano-silicon is less than or equal to 100 nm, wherein the steps S100, S200 and S300 are all performed under the protection of an inert gas, the method further comprises the following step: during the gas-phase deposition reaction, passing the carrier gas into the gas-phase reactor through a second gas inlet of the gas-phase reactor, the preheating temperature is 80-600 ℃, the reaction silicon-based gas is at least one of dichlorosilane and trichlorosilane, the carrier gas is one of hydrogen, argon and nitrogen.

2. The method of claim 1, wherein, The temperature of the gas-phase deposition reaction is 200-1200 ℃.

3. The method of claim 2, wherein, The pressure of the gas-phase deposition reaction is 0-0.5 MPa.

4. The method of claim 1, wherein, The molar concentration of the reaction silicon-based gas in the gas-phase reactor is 40-80 mol%.

5. The method of claim 4, wherein, The average particle size of the nano-silicon is 30-100 nm.

6. The method according to any one of claims 1 to 5, characterized in that, The separation is completed by a collector, and the collector is an electrostatic collector or a cloth bag collector.

7. The method according to any one of claims 1 to 5, characterized in that, The method further comprises the following steps: filtering the tail gas and then passing the filtered tail gas into a tail gas treatment device, wherein the filtering is performed by using a cloth bag dust collector, an inorganic filter membrane or an organic filter membrane.

8. Nanosilicon characterized in that, The nano-silicon is prepared by the method according to any one of claims 1-7, the average particle size of the nano-silicon is less than or equal to 100 nm, and the surface oxygen content of the nano-silicon is less than or equal to 1.0 wt%.

9. A lithium-ion battery anode material, characterized in that, The nano-silicon according to claim 8 is provided.

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