Nano silicon-carbon composite material as well as preparation method and application thereof

Abstract

The invention discloses a nano silicon-carbon composite material as well as a preparation method and application thereof. The nano silicon-carbon composite material comprises: a core material comprising porous carbon and nano silicon particles distributed on the surface and in pores of the porous carbon; the first low-temperature carbon coating layer is coated on the core material; the second low-temperature carbon coating layer is coated on the first low-temperature carbon coating layer; in addition, the content of SiC in the nano silicon-carbon composite material is below 1wt%. The nano silicon-carbon composite material provided by the invention has the advantages of high gram volume, high capacity exertion, high first efficiency, long cycle life, low expansion coefficient and the like, and can be widely applied to nano silicon-carbon negative electrode materials, lithium ion battery negative electrodes or lithium ion batteries and other products.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a nano silicon-carbon composite material and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries, as a kind of energy storage devices with outstanding performance, are widely used in many fields such as new energy storage power systems, electric tools, new energy vehicles, military equipment, aerospace, etc. Nowadays, people have higher requirements for the energy density, rate performance, cycle performance, high and low temperature performance, etc. of the new generation of lithium ion batteries. In view of the development requirement of energy density, the most direct and effective method is to improve the specific capacity of electrode materials.

[0003] At present, silicon-carbon negative electrode materials are favored by the application market due to their high specific capacity, and the theoretical specific capacity of silicon-based negative electrode materials can reach 4200 mAh / g, and they also have a low lithium extraction potential, so they are a battery material with great application potential. However, the huge volume expansion shortens the cycle life of the battery and also limits the application of the material in high-end electronic devices. At the same time, a large amount of solid electrolyte interface film (SEI film) is formed in the first charge-discharge process of the silicon-based negative electrode material, which easily consumes active lithium ions and causes the reduction of the first coulombic efficiency. In summary, the silicon-carbon negative electrode material has defects such as low theoretical specific capacity of silicon, large volume expansion, short cycle life, and low first coulombic efficiency.

[0004] Some researchers provide a nano-silicon-carbon composite material for a secondary lithium battery, which is composed of a porous carbon matrix, a plating layer containing a transition metal element, and nano-silicon particles. The plating layer covers the inside of the pore channels of the porous carbon and the surface of the microspheres, avoiding the reaction of nano-silicon particles with the porous carbon matrix to form silicon carbide during deposition. The purpose is to reduce the irreversible capacity loss caused by the formation of SiC through physical isolation, but the plating layer reduces the proportion of lithium storage active substances inside the nano-silicon-carbon composite material, and the coating process is complex, easy to block the through holes, and also increases the preparation cost of the nano-silicon-carbon composite material. Some researchers provide a nano-silicon-carbon doped with metal elements and a preparation method and application thereof. By doping metal nitride in the porous carbon and depositing nano-silicon and carbon coating on the surface, a nano-silicon-carbon with spherical morphology and excellent conductivity is obtained. As a negative active material, it has high capacity and coulombic efficiency, and effectively inhibits the expansion rate of the pole piece during the charging and discharging cycle process, but the porous carbon needs to be doped in advance, and the overall process is complex and costly. Some researchers reduce the acetylene coating temperature by plasma enhanced chemical deposition (PECVD), but the equipment requirements are high, and currently only experimental preparation can be carried out, which cannot be mass-produced. In addition, it also has the disadvantages of low deposition rate, affecting the production efficiency of large-scale mass production, difficult process control, and parameter sensitivity. Moreover, the preparation method of the lithium-doped silicon-carbon composite material provided by this method is complex, although it is prepared by twice carbon coating, but the required temperature is high, and the capacity of silicon is low.

[0005] Therefore, it is a focus and difficulty in the industry of battery negative materials to prepare a silicon-based negative material with a simple preparation method, high silicon capacity, high initial efficiency, and long cycle performance. SUMMARY

[0006] The main purpose of the present application is to provide a nano-silicon-carbon composite material and a preparation method and application thereof to overcome the shortcomings of the prior art.

[0007] To achieve the above-mentioned purposes, the technical solutions adopted by the present application include: The first aspect of the present application provides a nano-silicon-carbon composite material, which comprises: a core material comprising porous carbon and nano-silicon particles distributed on the surface and in the pore channels of the porous carbon; a first low-temperature carbon coating layer coated on the core material and having a loose network structure; and a second low-temperature carbon coating layer coated on the first low-temperature carbon coating layer and filling the structural defects of the first low-temperature carbon coating layer; and the content of SiC in the nano-silicon-carbon composite material is below 1wt%.

[0008] The second aspect of the present application provides a preparation method of a nano-silicon-carbon composite material, which comprises: Depositing nano-silicon particles on the surface and inside the pores of the porous carbon by vapor deposition to form a core material; Coating a first low-temperature carbon coating layer on the surface of the core material by vapor deposition at a first temperature; Coating a second low-temperature carbon coating layer on the first low-temperature carbon coating layer by vapor deposition at a second temperature to obtain a nano-silicon / carbon composite material; wherein the second temperature is below the bonding reaction temperature of Si and C.

[0009] A third aspect of the present application provides a nano-silicon / carbon negative electrode material, which comprises the nano-silicon / carbon composite material described above.

[0010] A fourth aspect of the present application provides a lithium ion negative electrode, which comprises the nano-silicon / carbon negative electrode material described above.

[0011] A fifth aspect of the present application provides a lithium ion battery, which comprises a negative electrode, a positive electrode and an electrolyte, and the negative electrode comprises the lithium ion negative electrode described above.

[0012] Compared with the prior art, the present application has at least the following beneficial effects: (1) The preparation method of the nano-silicon / carbon composite material provided by the present application can significantly improve the electrochemical performance of the material by simple two low-temperature carbon coating, so that the material has the advantages of high specific capacity, high capacity release, high initial efficiency, long cycle life and low expansion coefficient; especially in the case of the same specific capacity, the silicon content is less, the nano-silicon capacity release is higher, the cycle expansion is smaller, and the cycle performance of the material is better.

[0013] (2) From the perspective of industrialization, the preparation method of the nano-silicon / carbon composite material provided by the present application is simple, more energy-saving and emission-reducing, and can be produced on a large scale. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments described in the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0015] Figure 1 is a structure diagram of a nano-silicon / carbon composite material in a typical embodiment of the present application; Figure 2 is a SEM diagram of a nano-silicon / carbon composite material in embodiment 1 of the present application; Figure 3 is a first charge-discharge curve diagram of a lithium ion button cell prepared by using the nano-silicon / carbon composite material in embodiment 1 of the present application as a negative electrode material. DETAILED DESCRIPTION

[0016] In view of the problems in the prior art, the inventors of the present application have conducted extensive and in-depth research and provide a nano silicon-carbon composite material, a preparation method and application thereof.

[0017] The technical solutions, implementation processes and principles thereof will be further explained and described as follows.

[0018] The first aspect of the present application provides a nano silicon-carbon composite material, which comprises: a core material comprising porous carbon and nano silicon particles distributed on the surface and in the pores of the porous carbon; a first low-temperature carbon coating layer coated on the core material and having a loose network structure; a second low-temperature carbon coating layer coated on the first low-temperature carbon coating layer and filling the structural defects of the first low-temperature carbon coating layer; and the SiC content in the nano silicon-carbon composite material is below 1 wt%.

[0019] In some embodiments, the porous carbon, the first low-temperature carbon coating layer and the second low-temperature carbon coating layer are all composed of amorphous carbon.

[0020] In some embodiments, the structural disorder degree ID / IG of the porous carbon is between 0.8 and 1.3.

[0021] In some embodiments, the structural disorder degree ID / IG of the first low-temperature carbon coating layer is between 1.5 and 2.0.

[0022] In some embodiments, the structural disorder degree ID / IG of the second low-temperature carbon coating layer is between 1.5 and 2.0.

[0023] In some embodiments, the diameter of the core material ranges from 6 to 10 μm, the thickness of the first low-temperature carbon coating layer is 10-50 nm, and the thickness of the second low-temperature carbon coating layer is 5-20 nm.

[0024] In some embodiments, the D50 of the nano silicon-carbon composite material is 6-10 μm. 50 In some embodiments, the D50 of the nano silicon-carbon composite material is 6-10 μm.

[0025] In some embodiments, the specific surface area of the nano silicon-carbon composite material is 2-6 m 2 / g.

[0026] In some embodiments, the loose bulk density of the nano silicon-carbon composite material is 0.2-0.5 g / cm 3 .

[0027] In some embodiments, the tap density of the nano silicon-carbon composite material is 0.81±0.1 g / cc.

[0028] In some embodiments, the nanosilicon-carbon composite material has an electrical conductivity of > 0.35 S / cm.

[0029] In some embodiments, the nanosilicon-carbon composite material has a silicon capacity of > 3900 mAh / g.

[0030] In some embodiments, the nanosilicon-carbon composite material has a silicon content of 46-55 wt%, a deposited silicon content of 45-54 wt%, a floating silicon content of 0-0.6 wt%, and a carbon content of 45-54 wt%. The deposited silicon refers to silicon deposited inside the porous carbon, and mainly consists of nanosilicon particles. The floating silicon refers to nanosilicon particles that are not deposited inside the porous carbon, but mainly deposited on the surface of the porous carbon.

[0031] In some embodiments, the nanosilicon-carbon composite material has a SiC content of < 1 wt%.

[0032] The second aspect of the present application provides a method for preparing a nanosilicon-carbon composite material, which comprises: depositing nanosilicon particles on the surface and inside the pores of the porous carbon using a gas deposition method to form a core material; coating a first low-temperature carbon coating layer on the surface of the core material using a gas deposition method at a first temperature; coating a second low-temperature carbon coating layer on the first low-temperature carbon coating layer using a gas deposition method at a second temperature to obtain the nanosilicon-carbon composite material; wherein the second temperature is below the bonding reaction temperature of Si and C. The bonding reaction temperature of Si and C is generally 540℃.

[0033] In some cases, the first temperature < the second temperature.

[0034] In some embodiments, the method for preparing the nanosilicon-carbon composite material specifically comprises: placing the porous carbon into a reaction chamber, increasing the temperature in the reaction chamber to the deposition temperature of the nanosilicon particles at a temperature increasing rate of 2-8℃ / min under a protective atmosphere, and then introducing silane gas to deposit nanosilicon particles on the surface and inside the pores of the porous carbon to obtain the core material.

[0035] Further, the protective atmosphere is formed by introducing a protective gas into the reaction chamber at a flow rate of 15-25 slm.

[0036] Further, the protective gas comprises any one or a combination of nitrogen, argon, and helium.

[0037] Further, the deposition temperature of the nanosilicon particles is 450-500℃, and the deposition time is 135-300 min.

[0038] Further, the silane gas comprises any one or a combination of monosilane and disilane.

[0039] Further, the flow rate of the silane gas is 1.5-4.5 slm.

[0040] Further, the average pore size of the porous carbon is 1.0-2.0 nm, and the specific surface area is 1500-2500 m 2 / g.

[0041] In some embodiments, the preparation method of the nanosilicon-carbon composite material specifically comprises: adjusting the temperature in the reaction chamber to a first temperature under a protective atmosphere, and then introducing a carbon source gas, so as to perform first low-temperature carbon coating on the surface of the core material by fluidized bed chemical vapor deposition, thereby forming the first low-temperature carbon coating layer.

[0042] Further, the first temperature is 450-530℃.

[0043] Further, the time for the first low-temperature carbon coating is 90-180 min.

[0044] Further, the carbon source gas comprises any one or a combination of propylene, acetylene, and ethylene.

[0045] Further, the flow rate of the carbon source gas during the first low-temperature carbon coating is 1.5-4.5 slm.

[0046] Further, the first low-temperature carbon coating is performed in a fluidized bed vapor deposition reactor.

[0047] In some embodiments, the preparation method of the nanosilicon-carbon composite material specifically comprises: adjusting the temperature in the reaction chamber to a second temperature under a protective atmosphere, and continuing to introduce the carbon source gas, so as to perform second low-temperature carbon coating on the first low-temperature carbon coating layer, thereby forming the second low-temperature carbon coating layer, and obtaining the nanosilicon-carbon composite material.

[0048] Further, the second temperature is 490-530℃.

[0049] Further, the time for the second low-temperature carbon coating is 4-6 h.

[0050] In the present application, when performing the first low-temperature carbon coating or the second low-temperature carbon coating, a temperature exceeding the first temperature or the second temperature will affect the capacity of silicon, and a temperature lower than the first temperature or the second temperature will result in low carbon coating efficiency and difficult control of surface defects, so it is necessary to control the temperature of the first low-temperature carbon coating and the second low-temperature carbon coating within a suitable range.

[0051] Further, the flow rate of the carbon source gas in the second low-temperature carbon coating process is 1.0-2.5 slm.

[0052] In the carbon coating process of the present application, if the flow rate of the carbon source gas is too high, part of the carbon source gas cannot be fully reacted on the surface of the material, forming a loose or incomplete carbon layer, and the utilization rate of the carbon source gas is reduced, and the cost is increased; if the flow rate of the carbon source gas is too low, the reaction is not sufficient and uniform locally, affecting the preparation of the material.

[0053] Further, the second low-temperature carbon coating is carried out in a gas phase deposition rotary furnace.

[0054] In some more specific embodiments, the preparation method of the nano-silicon carbon composite material specifically comprises the following steps: S1, the porous carbon material is added to the fluidized bed CVD reaction cavity, a protective gas is introduced, and then the temperature is raised to a deposition temperature of 450-500℃ at a temperature raising rate of 2-8℃ / min; S2, then the silane gas is introduced to deposit nano-silicon particles on the surface and inside the pores of the porous carbon to form a core material; wherein the flow rate of the silane gas is 1.5-4.5 slm, and the deposition time is 220-300 min; S3, under the protective atmosphere, the temperature in the reaction cavity is adjusted to a first temperature, the carbon source gas is introduced, and the fluidized bed chemical vapor deposition method is used to carry out first low-temperature carbon coating on the core material to form a primary carbon coating layer; wherein the temperature of the first low-temperature carbon coating is 450-530℃, the time is 90-180 min, and the flow rate of the carbon source gas is 1.5-4.5 slm; S4, then it is added to a gas phase deposition rotary furnace, under the protective atmosphere, the temperature in the reaction cavity is adjusted to a second temperature, the carbon source gas is continuously introduced, and second low-temperature carbon coating is carried out on the primary carbon coating layer to form a second low-temperature carbon coating layer, thereby preparing the nano-silicon carbon composite material; wherein the second temperature is 490-530℃, the time is 4-6h, the flow rate of the carbon source gas is 1.0-2.5 slm, and the second temperature is below the bonding reaction temperature of Si and C.

[0055] In the first low-temperature carbon-coating process of the application, the strong gas-solid mixing characteristics of the fluidized bed enable the carbon source gas (such as acetylene) to be uniformly deposited on the silicon / porous carbon surface dynamically, forming a loose network structure of the primary carbon-coating layer. The low-temperature advantage inhibits the growth of silicon grains, and the carbon-coating layer is mainly amorphous, with high flexibility, which can adapt to the volume change of silicon. In addition, the low temperature avoids the collapse of the porous carbon skeleton, preserving the ion diffusion channels. In the second low-temperature carbon-coating process, the rotary furnace low-temperature carbon-coating strengthens and repairs the carbon-coating layer, further repairing possible local defects (such as micro-cracks, uneven thickness) of the carbon-coating layer. Specifically, the main reason for improving the material performance through the two low-temperature carbon-coating processes is: first, under the condition of low-temperature coating, less SiC is produced by the bonding of nanosilicon and carbon, avoiding the agglomeration of part of the nanosilicon at high temperature, which is more conducive to the capacity of silicon. Under the same silicon content, the capacity utilization rate is 4%~8% higher than that under high-temperature conditions; second, under the same gram capacity, the silicon content is less, and the nanosilicon capacity is higher, making the cycle expansion smaller and the cycle expansion performance of the material better; in addition, the first low-temperature carbon-coating constructs a loose carbon network, reserving part of the silicon-carbon expansion space, and the second low-temperature carbon-coating continues to deposit and fill defects, which can well inhibit the electrolyte side reaction.

[0056] The structure of the nanosilicon-carbon composite material of the application is shown in Figure 1 The structure of the nanosilicon-carbon composite material of the application is shown in

[0057] Therefore, the nanosilicon-carbon composite material prepared by the application can form a multi-level carbon-coating layer to protect the nanosilicon under the condition of two low-temperature carbon-coating processes, can also reserve certain pores to enhance the ion diffusion efficiency, and can further inhibit the continuous generation of SiC and the growth of silicon grains, so that the capacity of silicon is significantly improved, and the cycle expansion performance of the material is significantly improved.

[0058] The third aspect of the application provides a nanosilicon-carbon negative material, which comprises the above-mentioned nanosilicon-carbon composite material.

[0059] The fourth aspect of the application provides a lithium ion negative electrode, which comprises the above-mentioned nanosilicon-carbon negative material.

[0060] The fifth aspect of the application provides a lithium ion battery, which comprises a negative electrode, a positive electrode and an electrolyte, and the negative electrode comprises the above-mentioned lithium ion negative electrode.

[0061] In some embodiments, the silicon capacity of the nano-silicon carbon negative electrode material in the lithium ion battery is greater than 3900 mAh / g. In the prior art, the silicon carbon capacity of the nano-silicon carbon composite material is normally less than 3750 mAh / g, while the nano-silicon carbon capacity is obviously improved by twice low-temperature carbon coating in the present application, and the nano-silicon capacity of the porous carbon is greater than 3900 mAh / g by fluidized bed CVD deposition.

[0062] In some embodiments, the first coulombic efficiency of the lithium ion battery is greater than 93%.

[0063] In some embodiments, the capacity retention rate of the lithium ion battery is greater than 99% after 200 cycles at a voltage of 1.5 V and a 0.1C rate.

[0064] In some embodiments, the lithium ion battery comprises a lithium ion button cell.

[0065] In order to make the purpose, technical solutions and advantages of the present application more clear, the present application is further described in detail below in combination with examples. It should be understood that the specific examples described herein are only used to explain the present application and not to limit the present application. Those skilled in the art can modify or replace equivalently without departing from the spirit and scope of the present application based on the understanding of the technical solutions of the present application, which should be covered within the protection scope of the present application.

[0066] The specific experimental steps or conditions not mentioned in the examples can be performed according to the conventional experimental steps described in the literature in the art or the operation or conditions. The reagents or instruments not mentioned by the manufacturer can be obtained by market purchase. The commercial selection of the remaining raw materials and instruments not mentioned is a conventional selection, which does not involve the core technical means of the present application.

[0067] For example, the application example of the present application uses a blue 5V / 10mA type battery tester to test the electrochemical performance of the button cell.

[0068] The model of the fluidized bed CVD reactor is Nuomet FBCVD-20; the model of the CVD rotary furnace is DM3060.

[0069] The purity of N2 used in the examples and comparative examples of the present application is 99.999%; the purity of SiH4 is 99.9999%; the purity of acetylene is 99.99%; the purity of propylene is 99.999%; the purity of ethylene is 99.999%; the model of the porous carbon material is T03, and the manufacturer is Fujian Yuanli Activated Carbon Co., Ltd.

[0070] Example 1 1.1 kg of nano-silicon with an average pore size of 2 nm and a specific surface area of 1800 m 2The porous carbon material with a pore volume of 0.5 g was added into a fluidized bed CVD reaction cavity; a protective gas N2 was introduced at a flow rate of 18 slm, and the stirring rate was 150 rpm, and then the temperature was increased to 470 ℃ at a temperature increasing rate of 5 ℃ / min; then the introduction of SiH4 was started, the flow rate of SiH4 was 3.3 slm, and the reaction time was 269 min, and after the reaction was completed, the core material was obtained; the temperature was increased to 510 ℃, the core material was coated with carbon by acetylene, the flow rate of acetylene introduced was 3.3 slm, the reaction time was 120 min, and the nano silicon-carbon material after the first carbon coating was obtained; then the nano silicon-carbon material was added into a CVD rotary furnace, the temperature was kept at 510 ℃ under the atmosphere of the protective gas N2, 1.1 slm of acetylene was introduced, the second low-temperature carbon coating was carried out, the reaction time was 4.5 h, and finally the finished product of the nano silicon-carbon composite material was obtained.

[0071] The SEM image of the nano silicon-carbon composite material prepared in the example is shown in FIG. 1. Figure 2 As can be seen from the SEM image, the surface of the prepared nano silicon-carbon composite material has no obvious defects and is not rough.

[0072] The structural disorder degree of the nano silicon-carbon composite material of the example was obtained by Raman spectrum test.

[0073] The specific surface area was calculated by the BET method by measuring the adsorption amount of inert gas (nitrogen N2) of the solid material at low temperature (liquid nitrogen temperature, -196 °C).

[0074] The loose bulk density was measured by the natural piling method: the powder was allowed to flow freely from a standard funnel to fill a standard measuring cup with a known volume. After scraping off the excess powder at the cup mouth, the mass of the powder in the cup was weighed, and the loose bulk density was calculated by the ratio of the mass to the volume. The tap density was obtained by testing the powder particles after rearrangement by mechanical vibration to eliminate voids to achieve a tight piling state.

[0075] The conductivity was mainly realized by pressing and molding combined with electrical measurement, and was obtained by testing by the four-probe method.

[0076] The deposited silicon content and the floating silicon content were obtained by thermogravimetric method; in the example, the mass content of the floating silicon was 0.32%, and the floating silicon content was small, indicating that the nano silicon was uniformly deposited on the surface and in the pores of the porous carbon, and the deposition effect was good.

[0077] The D50 particle size test was based on the scattering phenomenon of particles on laser (Fraunhofer diffraction and Mie scattering theory), the scattering light intensity at different angles was measured by a detector, and the particle size distribution was calculated by using a suitable optical model and mathematical algorithm. The mass content of SiC was obtained by X-ray diffraction (XRD) method.

[0078] The diameter of the core material of the nanosilicon-carbon composite material of the present example is 8.6 pm, the thickness of the first low-temperature carbon coating layer is about 30 nm, and the thickness of the second low-temperature carbon coating layer is 10 nm.

[0079] In the present example, the relevant data of the obtained nanosilicon-carbon composite material are shown in Table 1.

[0080] Example 2 1.1 kg of porous carbon material with an average pore size of 2 nm and a specific surface area of 1800 m 2 / g was weighed and added to a fluidized bed CVD reaction cavity; at the same time, protective gas N2was introduced at a flow rate of 18 slm, and the stirring rate was 150 rpm, and then the temperature was raised to 470°C at a temperature raising rate of 5°C / min; then SiH4was introduced, the flow rate of SiH4was 3.3 slm, the reaction time was 269 min, and after the reaction was completed, the core material was obtained; the temperature was raised to 530°C, and the core material was coated with carbon by acetylene, the flow rate of acetylene introduced was 3.3 slm, the reaction time was 100 min, and the nanosilicon-carbon material after the first carbon coating was obtained; then the nanosilicon-carbon material was added to a CVD rotary furnace, the temperature was kept unchanged at 530°C under the atmosphere of protective gas N2, 1.1 slm of acetylene was introduced, and the second low-temperature carbon coating was performed, the reaction time was 4 h, and finally the finished nanosilicon-carbon composite material was obtained.

[0081] The diameter of the core material of the nanosilicon-carbon composite material of the present example is 8.5 pm, the thickness of the first low-temperature carbon coating layer is about 30 nm, and the thickness of the second low-temperature carbon coating layer is about 10 nm.

[0082] In the present example, the relevant data of the obtained nanosilicon-carbon composite material are shown in Table 1.

[0083] Example 3 1.1 kg of porous carbon material with an average pore size of 2 nm and a specific surface area of 1800 m 2 / g was weighed and added to a fluidized bed CVD reaction cavity; at the same time, protective gas N2was introduced at a flow rate of 18 slm, and the stirring rate was 150 rpm, and then the temperature was raised to 470°C at a temperature raising rate of 5°C / min; then SiH4was introduced, the flow rate of SiH4was 3.3 slm, the reaction time was 269 min, and after the reaction was completed, the core material was obtained; the temperature was raised to 530°C, and the core material was coated with carbon by acetylene, the flow rate of acetylene introduced was 3.3 slm, the reaction time was 100 min, and the nanosilicon-carbon material after the first carbon coating was obtained; then the nanosilicon-carbon material was added to a CVD rotary furnace, the temperature was kept unchanged at 530°C under the atmosphere of protective gas N2, 1.1 slm of acetylene was introduced, and the second low-temperature carbon coating was performed, the reaction time was 4 h, and finally the finished nanosilicon-carbon composite material was obtained.

[0084] The diameter of the core material of the nanosilicon-carbon composite material of this example is 8.7 μm, the thickness of the first low-temperature carbon coating layer is about 40 nm, and the thickness of the second low-temperature carbon coating layer is about 15 nm.

[0085] In this example, the relevant data of the obtained nanosilicon-carbon composite material are shown in Table 1.

[0086] Example 4 1.1 kg of porous carbon material with an average pore size of 2 nm and a specific surface area of 1800 m 2 / g was weighed and added to a fluidized bed CVD reaction cavity; at the same time, protective gas N2 was introduced at a flow rate of 18 slm, and the stirring rate was 150 rpm, and then the temperature was raised to 470°C at a temperature raising rate of 5°C / min; then SiH4 was introduced, the flow rate of SiH4 was 3.3 slm, and the reaction time was 269 min, and after the reaction was completed, the core material was obtained; the temperature was lowered to 450°C, and the core material was subjected to carbon coating with acetylene, the flow rate of acetylene introduced was 3.3 slm, and the reaction time was 180 min, and the nanosilicon-carbon material after the first carbon coating was obtained; then the nanosilicon-carbon material was added to a CVD rotary furnace, and under the atmosphere of protective gas N2, the temperature was raised to 530°C, 1.1 slm of acetylene was introduced, the second low-temperature carbon coating was performed, and the reaction time was 4 h, and finally the finished nanosilicon-carbon composite material was obtained.

[0087] The diameter of the core material of the nanosilicon-carbon composite material of this example is 8.7 μm, the thickness of the first low-temperature carbon coating layer is about 50 nm, and the thickness of the second low-temperature carbon coating layer is about 10 nm.

[0088] In this example, the relevant data of the obtained nanosilicon-carbon composite material are shown in Table 1.

[0089] Example 5 1.1 kg of porous carbon material with an average pore size of 2 nm and a specific surface area of 1800 m 2 / g was weighed and added to a fluidized bed CVD reaction cavity; at the same time, protective gas N2 was introduced at a flow rate of 18 slm, and the stirring rate was 150 rpm, and then the temperature was raised to 470°C at a temperature raising rate of 5°C / min; then SiH4 was introduced, the flow rate of SiH4 was 3.3 slm, and the reaction time was 269 min, and after the reaction was completed, the core material was obtained; the temperature was lowered to 450°C, and the core material was subjected to carbon coating with acetylene, the flow rate of acetylene introduced was 3.3 slm, and the reaction time was 180 min, and the nanosilicon-carbon material after the first carbon coating was obtained; then the nanosilicon-carbon material was added to a CVD rotary furnace, and under the atmosphere of protective gas N2, the temperature was raised to 530°C, 1.1 slm of acetylene was introduced, the second low-temperature carbon coating was performed, and the reaction time was 4 h, and finally the finished nanosilicon-carbon composite material was obtained.

[0090] The diameter of the core material of the nanosilicon-carbon composite material of the present example is 8.7 μm, the thickness of the first low-temperature carbon coating layer is about 30 nm, and the thickness of the second low-temperature carbon coating layer is about 10 nm.

[0091] In the present example, the relevant data of the obtained nanosilicon-carbon composite material are shown in Table 1.

[0092] Example 6 1.1 kg of porous carbon material with an average pore size of 2 nm and a specific surface area of 1800 m 2 / g was weighed and added to the fluidized bed CVD reaction cavity; at the same time, protective gas N2 was introduced at a flow rate of 18 slm, and the stirring rate was 150 rpm, and then the temperature was raised to 470 °C at a temperature raising rate of 5 °C / min; then SiH4 was introduced, the flow rate of SiH4 was 3.3 slm, the reaction time was 269 min, and after the reaction was completed, the core material was obtained; the temperature was raised to 510 °C, and the core material was coated with propylene, the flow rate of propylene introduced was 3.3 slm, the reaction time was 130 min, and the nanosilicon-carbon material after the first carbon coating was obtained; then the nanosilicon-carbon material was added to the CVD rotary furnace, under the atmosphere of protective gas N2, the temperature was kept at 510 °C, 1.1 slm of propylene was introduced, and the second low-temperature carbon coating was carried out, the reaction time was 5 h, and finally the finished nanosilicon-carbon composite material was obtained.

[0093] The diameter of the core material of the nanosilicon-carbon composite material of the present example is 8.8 μm, the thickness of the first low-temperature carbon coating layer is about 30 nm, and the thickness of the second low-temperature carbon coating layer is about 10 nm.

[0094] In the present example, the relevant data of the obtained nanosilicon-carbon composite material are shown in Table 1.

[0095] Example 7 1.1 kg of porous carbon material with an average pore size of 2 nm and a specific surface area of 1800 m 2 / g of porous carbon material was added to a fluidized bed CVD reaction chamber; simultaneously, protective gas N2 was introduced at a flow rate of 18 slm and a stirring rate of 150 rpm, and then the temperature was increased to 470℃ at a heating rate of 5℃ / min; then silane was introduced at a flow rate of 3.3 slm and the reaction time was 135 min. After the reaction was complete, the core material was obtained; the temperature was raised to 510℃, and acetylene carbon coating was performed on the core material at a flow rate of 3.3 slm and the reaction time was 120 min, resulting in nano-silicon-carbon material with the first carbon coating. Then, the nano-silicon-carbon material was added to a CVD rotary furnace, and under a protective gas N2 atmosphere, the temperature was kept constant at 510℃, and 1.1 slm of ethylene was introduced for a second low-temperature carbon coating, with a reaction time of 4 h, finally obtaining the finished nano-silicon-carbon composite material.

[0096] In this embodiment, the core material of the nano-silicon-carbon composite material has a diameter of 8.8 μm, the thickness of the first low-temperature carbon coating layer is about 30 nm, and the thickness of the second low-temperature carbon coating layer is about 10 nm.

[0097] In this embodiment, the relevant data of the obtained nano-silicon-carbon composite material are shown in Table 1.

[0098] Comparative Example 1 Weigh 1.1 kg, with an average pore size of 2 nm and a specific surface area of ​​1800 m². 2 / g of porous carbon material was added to a fluidized bed CVD reaction chamber; simultaneously, protective gas N2 was introduced at a flow rate of 18 slm and a stirring rate of 150 rpm, and then the temperature was increased to 470℃ at a heating rate of 5℃ / min; then SiH4 was introduced at a flow rate of 3.3 slm and the reaction time was 269 min. After the reaction was complete, the core material was obtained; the temperature was raised to 600℃, and acetylene carbon coating was performed on the core material at a flow rate of 3.3 slm and a reaction time of 80 min, resulting in nano-silicon-carbon material after the first carbon coating. Then, the nano-silicon-carbon material was added to a CVD rotary furnace, and under a protective gas N2 atmosphere, the temperature was kept constant at 600℃, and 1.1 slm of acetylene was introduced for a second low-temperature carbon coating, with a reaction time of 3 h, finally obtaining the finished nano-silicon-carbon composite material.

[0099] In this comparative example, the relevant data of the obtained nano-silicon-carbon composite material are shown in Table 1.

[0100] Comparative Example 2 Weigh 1.1 kg, with an average pore size of 2 nm and a specific surface area of ​​1800 m². 2 / g of porous carbon material was added to a fluidized bed CVD reaction chamber; simultaneously, protective gas N2 was introduced at a flow rate of 18 slm and a stirring rate of 150 rpm, and then the temperature was increased to 470℃ at a heating rate of 5℃ / min; then SiH4 was introduced at a flow rate of 3.3 slm and the reaction time was 269 min. After the reaction was complete, the core material was obtained; the temperature was raised to 580℃, and acetylene carbon coating was performed on the core material at a flow rate of 3.3 slm and a reaction time of 80 min, resulting in nano-silicon-carbon material with the first carbon coating. Then, the nano-silicon-carbon material was added to a CVD rotary furnace, and under a protective gas N2 atmosphere, the temperature was kept constant at 580℃, and 1.1 slm of acetylene was introduced for a second low-temperature carbon coating, with a reaction time of 3.5 h, finally obtaining the finished nano-silicon-carbon composite material.

[0101] In this comparative example, the relevant data of the obtained nano-silicon-carbon composite material are shown in Table 1.

[0102] Comparative Example 3 Weigh 1.1 kg, with an average pore size of 2 nm and a specific surface area of ​​1800 m². 2 / g of porous carbon material was added to a fluidized bed CVD reaction chamber; simultaneously, protective gas N2 was introduced at a flow rate of 18 slm and a stirring rate of 150 rpm, and then the temperature was increased to 470℃ at a heating rate of 5℃ / min; then SiH4 was introduced at a flow rate of 3.3 slm and the reaction time was 269 min. After the reaction was complete, the core material was obtained; the temperature was raised to 550℃, and acetylene carbon coating was performed on the core material at a flow rate of 3.3 slm and a reaction time of 90 min, resulting in nano-silicon-carbon material with the first carbon coating. Then, the nano-silicon-carbon material was added to a CVD rotary furnace, and under a protective gas N2 atmosphere, the temperature was kept constant at 550℃, and 1.1 slm of acetylene was introduced for a second low-temperature carbon coating, with a reaction time of 4 h, finally obtaining the finished nano-silicon-carbon composite material.

[0103] In this comparative example, the relevant data of the obtained nano-silicon-carbon composite material are shown in Table 1.

[0104] Comparative Example 4 Weigh 1.1 kg, with an average pore size of 2 nm and a specific surface area of ​​1800 m². 2The porous carbon material with a specific surface area of 2000 m2 / g was added into a fluidized bed CVD reaction cavity; at the same time, a protective gas N2was introduced at a flow rate of 18 slm, and the stirring rate was 150 rpm, and then the temperature was increased to 470 ℃ at a temperature increasing rate of 5 ℃ / min; then the introduction of SiH4was started, the flow rate of SiH4was 3.3 slm, the reaction time was 269 min, and after the reaction was completed, the core material was obtained; the temperature was increased to 510 ℃, the core material was coated with carbon by acetylene, the flow rate of acetylene introduced was 3.3 slm, the reaction time was 120 min, and then the nano-silicon-carbon material after the first carbon coating was obtained; then the nano-silicon-carbon material was added into a CVD rotary furnace, the temperature was increased to 580 ℃ under the atmosphere of the protective gas N2, 1.1 slm of acetylene was introduced, the second low-temperature carbon coating was carried out, the reaction time was 3.6 h, and finally the finished product of the nano-silicon-carbon composite material was obtained.

[0105] In the present comparative example, the related data of the obtained nano-silicon-carbon composite material are shown in Table 1.

[0106] Based on Comparative Example 1, Comparative Example 2 and Comparative Example 4, it can be seen that neither the first high-temperature carbon coating nor the twice high-temperature carbon coating is conducive to the capacity of silicon.

[0107] Comparative Example 5 In the present comparative example, the method for preparing the core material is the same as that in Example 1, and when the first carbon coating is carried out, the core material is coated with carbon by acetylene at 580 ℃, the flow rate of acetylene introduced is 3.3 slm, and the reaction time is 120 min, and then the nano-silicon-carbon material after the first carbon coating is obtained. Then the nano-silicon-carbon material after the first carbon coating is coated with carbon by the second low-temperature carbon coating in the same manner as in Example 1.

[0108] In the present comparative example, the related data of the obtained nano-silicon-carbon composite material are shown in Table 1.

[0109] Comparative Example 6 In the present comparative example, the method for preparing the core material is the same as that in Example 1, and when the first carbon coating is carried out, the core material is coated with carbon by acetylene at 440 ℃, the flow rate of acetylene introduced is 3.3 slm, and the reaction time is 120 min, and then the nano-silicon-carbon material after the first carbon coating is obtained. Then the nano-silicon-carbon material after the first carbon coating is coated with carbon by the second low-temperature carbon coating in the same manner as in Example 1.

[0110] In the present comparative example, the related data of the obtained nano-silicon-carbon composite material are shown in Table 1.

[0111] Comparative Example 7 The method for preparing the core material and the first carbon coating in this comparative example is the same as that in Example 1, but after the first carbon coating is completed, the nano-silicon-carbon material after the first carbon coating is added into a CVD rotary furnace, under a protective gas N2 atmosphere, heated to 580°C, 1.1 slm of acetylene is introduced, the second low-temperature carbon coating is carried out, the reaction time is 4.5 h, and finally the finished nano-silicon-carbon composite material is obtained.

[0112] In this comparative example, the related data of the obtained nano-silicon-carbon composite material are shown in Table 1.

[0113] Comparative Example 8 The method for preparing the core material and the first carbon coating in this comparative example is the same as that in Example 1, but after the first carbon coating is completed, the nano-silicon-carbon material after the first carbon coating is added into a CVD rotary furnace, under a protective gas N2 atmosphere, heated to 580°C, 1.1 slm of acetylene is introduced, the second low-temperature carbon coating is carried out, the reaction time is 4.5 h, and finally the finished nano-silicon-carbon composite material is obtained.

[0114] In this comparative example, the related data of the obtained nano-silicon-carbon composite material are shown in Table 1.

[0115] Comparative Example 9 1.1 kg of porous carbon material with an average pore size of 2 nm and a specific surface area of 2300 m 2 / g is weighed and added into a fluidized bed CVD reaction cavity; at the same time, protective gas N2 is introduced, the N2 flow rate is 18 slm, the stirring rate is 150 rpm, then the temperature is raised to 470°C at a rate of 5°C / min; then SiH4 is introduced, the SiH4 flow rate is 3.3 slm, the reaction time is 300 min, after the reaction is completed, the core material is obtained; the temperature is raised to 580°C, the core material is acetylene carbon coated, the acetylene flow rate is 3.3 slm, the reaction time is 80 min, the nano-silicon-carbon material after the first carbon coating is obtained, then the nano-silicon-carbon material is added into a CVD rotary furnace, under a protective gas atmosphere, the temperature is kept at 580°C, 1.1 slm of acetylene is introduced, the second low-temperature carbon coating is carried out, the reaction time is 3.5 h, and finally the finished nano-silicon-carbon composite material is obtained.

[0116] From the results of Comparative Example 2 and Comparative Example 9, it can be seen that different specific surface areas of porous carbon and different deposition amounts of nano-silicon-carbon still show that high-temperature coating is not conducive to the capacity of silicon; if the same gram capacity is to be achieved, more silicon must be deposited on the porous carbon with a larger specific surface area, and this will also lead to greater silicon expansion.

[0117] In this comparative example, the related data of the obtained nano-silicon-carbon composite material are shown in Table 1.

[0118] Comparative Example 10 1.1 kg of porous carbon material with an average pore size of 2 nm and a specific surface area of 1800 m 2 / g was weighed and added to a fluidized bed CVD reaction chamber; at the same time, protective gas N2 was introduced at a flow rate of 18 slm, and the stirring rate was 150 rpm, and then the temperature was raised to 470℃ at a rate of 5℃ / min; then SiH4 was introduced, the flow rate of SiH4 was 3.3 slm, and the reaction time was 269 min; after the reaction was completed, the core material was obtained; the temperature was lowered to 440℃, and the core material was coated with carbon by introducing acetylene at a flow rate of 3.3 slm, and the reaction time was 120 min to obtain the nano-silicon-carbon material after the first carbon coating; then the nano-silicon-carbon material was added to a CVD rotary furnace, and under the protective gas N2 atmosphere, the temperature was raised to 480℃, 1.1 slm of acetylene was introduced, and the second low-temperature carbon coating was carried out, and the reaction time was 6 h, and finally the finished nano-silicon-carbon composite material was obtained.

[0119] In the present comparative example, the relevant data of the obtained nano-silicon-carbon composite material are shown in Table 1.

[0120] Application Example 1 The nano-silicon-carbon composite materials prepared in Examples 1-7 and Comparative Examples 1-10 were respectively dispersed in water with a certain proportion of conductive agent and binder, wherein the mass ratio of nano-silicon-carbon composite material: polyacrylic acid PAA: carbon nanotube CNT: conductive agent SP = 85:5:0.5:9.5, and after the slurry was prepared, it was scraped onto a copper foil and dried, rolled, and cut into pieces to obtain lithium ion negative electrode sheets.

[0121] A lithium ion button cell was obtained by assembling a simulated battery (shell model number 2016) in an argon-filled glove box, using the lithium ion negative electrode sheet as the working electrode, a lithium metal sheet as the counter electrode, Celgard 25000 of PP material as the separator, and 1.0M LiPF6 / EC:DEC:DMC (volume ratio 1:1:1) as the electrolyte.

[0122] The electrochemical performance of the lithium ion button cell was tested by a battery tester, the charging voltage was 1.5V, the discharge was to 0.005V, the current rate of the first cycle charging and discharging was 0.1C, and the current rate of the charging and discharging in the cycle test was 0.2C. The test results are shown in Table 2. The first charge-discharge curve of the lithium ion button cell prepared by using the nano-silicon-carbon composite material of Example 1 of the present application as the negative electrode material is shown in Figure 3

[0123] Table 1 Test results of nano-silicon-carbon composite materials of examples and comparative examples ; ​

[0124] Note: The data shown in the above table are the average values of the corresponding test data of multiple batches of products.

[0125] Table 2 Test results of lithium ion button cells prepared using the nanosilicon-carbon composite materials of Examples and Comparative Examples as anodes

[0126] Note: The data shown in the above table are the average values of the corresponding test data of multiple batches of products.

[0127] In addition, the inventors of the present case also refer to the foregoing examples, and other raw materials, process operations, process conditions described in the specification are tested, and all ideal results are obtained.

[0128] Although the present application has been described with reference to illustrative embodiments, those with ordinary skill in the art will appreciate that various other alterations, omissions, and / or additions can be made and equivalents can be substituted for elements of the embodiments without departing from the spirit and scope of the present application. Additionally, many modifications can be made to adapt a particular situation or material to the teachings of the present application without departing from the scope of the present application. Accordingly, the present application is not intended to be limited to the disclosed embodiments for carrying out this application, but rather, the scope of the application is to be accorded the broadest interpretation so as to encompass all embodiments falling within the scope of the appended claims. Furthermore, unless specifically stated otherwise, any use of the terms first, second, etc., do not indicate any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another.

Claims

1. A nano-silicon-carbon composite material, characterized in that, include: Nuclear materials, including porous carbon and nano-silicon particles distributed on the surface and within the pores of porous carbon; A first low-temperature carbon coating layer is applied to the core material and has a loose network structure. The second low-temperature carbon coating layer is applied over the first low-temperature carbon coating layer and fills the structural defects of the first low-temperature carbon coating layer. Furthermore, the SiC content in the nano-silicon-carbon composite material is below 1 wt%.

2. The nano-silicon-carbon composite material according to claim 1, characterized in that: The porous carbon, the first low-temperature carbon coating layer, and the second low-temperature carbon coating layer are all composed of amorphous carbon. And / or, the structural disorder of the porous carbon, ID / IG, is between 0.8 and 1.3; And / or, the structural disorder degree ID / IG of the first low-temperature carbon coating layer is between 1.5 and 2.0; And / or, the structural disorder degree ID / IG of the second low-temperature carbon coating layer is between 1.5 and 2.0; And / or, the diameter of the core material is in the range of 6~10μm, the thickness of the first low-temperature carbon coating layer is 10~50nm, and the thickness of the second low-temperature carbon coating layer is 5~20nm; And / or, the D of the nano-silicon-carbon composite material 50 The particle size is 6~10μm; And / or, the specific surface area of ​​the nano-silicon-carbon composite material is 2~6m². 2 / g; And / or, the loose packing density of the nano-silicon-carbon composite material is 0.2~0.5 g / cm³. 3 ; And / or, the tap density of the nano-silicon-carbon composite material is 0.81 ± 0.1 g / cc; And / or, the electrical conductivity of the nano-silicon-carbon composite material is >0.35 S / cm; And / or, the silicon capacity of the nano-silicon-carbon composite material is above 3900 mAh / g; And / or, the silicon content in the nano-silicon-carbon composite material is 46-55 wt%, the content of deposited silicon is 45-55 wt%, the content of floated silicon is 0-0.6 wt%, and the carbon content is 45-54 wt%; And / or, the SiC content in the nano-silicon-carbon composite material is less than 1 wt%, preferably less than 0.5 wt%, and particularly preferably less than 0.3 wt%.

3. A method for preparing a nano-silicon-carbon composite material, characterized in that, include: Nano-silicon particles were deposited on the surface and inside the pores of porous carbon using vapor deposition to form a core material. At a first temperature, a first low-temperature carbon coating layer is deposited on the surface of the nuclear material using a vapor phase deposition method; At a second temperature, a second low-temperature carbon coating layer is deposited on the first low-temperature carbon coating layer using a vapor phase deposition method to obtain a nano-silicon-carbon composite material; wherein, the second temperature is below the bonding reaction temperature of Si and C.

4. The preparation method according to claim 3, characterized in that, Specifically, it includes: Porous carbon is placed in a reaction chamber, and under a protective atmosphere, the temperature inside the reaction chamber is raised to the deposition temperature of the nano-silicon particles at a heating rate of 2~8℃ / min. Then, silane gas is introduced to deposit nano-silicon particles on the surface and inside the pores of the porous carbon, thereby obtaining the core material. Preferably, the protective atmosphere is formed by introducing a protective gas into the reaction chamber at a flow rate of 15-25 slm. Preferably, the protective gas includes any one or more combinations of nitrogen, argon, and helium; Preferably, the deposition temperature of the silicon nanoparticles is 450~500℃, and the deposition time is 135~300min; Preferably, the silane gas includes any one or more combinations of silane and disilane; Preferably, the flow rate of the silane gas is 1.5~4.5 slm; Preferably, the porous carbon has an average pore size of 1.0~2.0 nm and a specific surface area of ​​1500~2500 m². 2 / g.

5. The preparation method according to claim 4, characterized in that, Specifically, it includes: Under a protective atmosphere, the temperature inside the reaction chamber is adjusted to a first temperature, and then a carbon source gas is introduced to form a first low-temperature carbon coating on the surface of the nuclear material by fluidized bed chemical vapor deposition. Preferably, the first temperature is 450~530℃; Preferably, the time for the first low-temperature carbon coating is 90~180 min; Preferably, the carbon source gas includes any one or more combinations of propylene, acetylene, and ethylene; Preferably, the flow rate of the carbon source gas during the first low-temperature carbon coating process is 1.5~4.5 slm; Preferably, the first low-temperature carbon coating is carried out in a fluidized bed vapor deposition reactor.

6. The preparation method according to claim 5, characterized in that, Specifically, it includes: Under a protective atmosphere, the temperature inside the reaction chamber is adjusted to a second temperature, and carbon source gas is continuously introduced to perform a second low-temperature carbon coating on the first low-temperature carbon coating layer, thereby forming the second low-temperature carbon coating layer and obtaining the nano-silicon-carbon composite material. Preferably, the second temperature is 490~530℃; Preferably, the second low-temperature carbon coating time is 4~6 hours; Preferably, the flow rate of the carbon source gas during the second low-temperature carbon coating process is 1.0~2.5 slm; Preferably, the second low-temperature carbon coating is carried out in a vapor deposition rotary furnace.

7. A nano-silicon-carbon anode material, characterized in that, Including the nano-silicon-carbon composite material as described in claim 1 or 2.

8. A lithium-ion anode, characterized in that, It includes the nano-silicon-carbon composite material according to any one of claims 1-2 or the nano-silicon-carbon anode material according to claim 7.

9. A lithium-ion battery, comprising a negative electrode, a positive electrode, and an electrolyte, characterized in that: The negative electrode comprises the lithium-ion negative electrode as described in claim 8.

10. The lithium-ion battery according to claim 9, characterized in that: The silicon capacity of the nano-silicon-carbon anode material in the lithium-ion battery is above 3900mAh / g. And / or, the initial coulombic efficiency of the lithium-ion battery is above 93%; And / or, the lithium-ion battery retains more than 99% of its capacity after 200 cycles at a voltage of 1.5V and a rate of 0.1C; And / or, the lithium-ion battery includes a lithium-ion coin cell.

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