SiOx / C composite negative electrode material and preparation method thereof

Abstract

The application discloses a SiOx / C composite negative electrode material, and belongs to the technical field of battery materials. The SiOx / C composite negative electrode material comprises SiOx and a C layer coated on the surface of the SiOx, the SiOx is uniformly distributed in the C, the X is less than 1, and the atomic ratio of C / Si is less than or equal to 2. The application further discloses a preparation method of the SiOx / C composite negative electrode material. The steps are as follows: S1, aerosolizing a precursor containing siloxane; S2, passing the precursor into an activation reactor protected by an inert atmosphere to perform activation, and keeping the temperature of the activation reactor between 600-800 DEG C; S3, carrying the activated precursor into a low-temperature reactor by a carrier gas to perform reaction, and obtaining a granular product, and the temperature of the reactor is 20-300 DEG C; and S4, carrying the granular product into a high-temperature reactor to perform calcination at 800-1300 DEG C to obtain the SiOx / C composite negative electrode material. The negative electrode material has a large capacity and a high first charge-discharge coulombic efficiency. The method does not need to use a catalyst, the raw material source is wide, and the obtained product is in a powder form and does not need to be crushed.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and particularly relates to a SiOx / C composite anode material and its preparation method. Background Technology

[0002] With the widespread application of lithium-ion batteries in electric vehicles, portable electronic devices, and other fields, the performance requirements for anode materials are becoming increasingly stringent. Traditional graphite anode materials, due to their relatively low theoretical specific capacity (372 mAh / g), are no longer sufficient to meet the demands of high-energy-density batteries.

[0003] Silicon-based materials have become a research hotspot due to their high theoretical specific capacity (approximately 4200 mAh / g). However, their significant volume expansion during charge and discharge leads to poor cycle stability, poor conductivity, susceptibility to electrolyte reactions, and structural collapse due to severe volume effects during charge and discharge cycles, limiting their practical applications. To overcome these shortcomings, researchers have introduced structural stabilizing elements (such as oxygen) into silicon-based materials. However, because the conductivity of silicon-oxygen anode materials remains poor and the initial charge-discharge coulombic efficiency is low, silicon-oxygen anode materials need to be used in combination with carbon-based anode materials such as graphite.

[0004] Currently, industrial silicon-oxygen anodes are mainly prepared through processes such as SiO vapor deposition, crushing, surface carbon coating, and graphite doping. Numerous protective measures are required at each stage to prevent the introduction of impurities and to reduce the contact between SiO and oxygen and water in the air, making the process complex and lengthy.

[0005] In his paper "Preparation of High-Capacity C / Si-OC Anode Material and Study on its Lithium-ion Intercalation / Deintercalation Mechanism," Liu Xiang of the National University of Defense Technology proposed using a composite material of C / SiOx generated by the pyrolysis of polysiloxane at high temperature as a lithium-ion battery anode material. This material exhibits high specific capacity and cycle stability, and its process is simpler compared to current industrial methods. However, this method has the following shortcomings.

[0006] (1) Because polysiloxanes contain low molecular weight components, these components will volatilize prematurely during direct pyrolysis, resulting in a low yield. Therefore, a platinum catalyst is used to pre-crosslink the polysiloxane at a lower temperature (120℃-200℃) to convert the liquid polysiloxane into solid organosilicon rubber, and then the temperature is raised to about 1000℃ for high-temperature pyrolysis. This crosslinking reaction is an addition reaction of Si-H bonds and unsaturated carbon-carbon bonds under the action of a platinum catalyst. Therefore, this method requires the use of expensive platinum catalysts (usually chloroplatinic acid), and also requires that the raw material polysiloxane must contain Si-H bonds and unsaturated carbon-carbon bonds, which limits the choice of raw materials.

[0007] (2) Since the high temperature cracks the silicone rubber, the resulting product is in block form and needs to be crushed before it can be used.

[0008] (3) Since the specific capacity of C / SiOx composite anode materials is mainly contributed by Si, the excess carbon introduced by the unsaturated carbon-carbon bonds in the raw materials results in an excessively high carbon content in the final product, with an average C / Si ratio of 3.5, which limits the specific capacity of C / SiOx. In addition, due to the limitation of the elemental composition in the raw materials, the O / Si ratio (x value) in the C / SiOx composite material obtained by the pyrolysis of polysiloxane is generally greater than 1, which limits the specific capacity of C / SiOx. The excess oxygen in the material reacts with lithium ions to generate irreversible products such as Li2O, resulting in a low coulombic efficiency of the first charge and discharge of lithium-ion batteries using C / SiOx as the anode material. Summary of the Invention

[0009] The purpose of this invention is to provide a SiOx / C composite anode material and its preparation method. This anode material has a large specific capacity and a high initial charge-discharge coulombic efficiency. The method does not require the use of a catalyst, the raw materials are widely available, and the obtained product is in powder form and does not require pulverization.

[0010] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0011] A SiOx / C composite anode material includes SiOx and a C layer coated on the surface of SiOx, wherein the SiOx is uniformly distributed in C, X < 1, and the atomic ratio of C / Si is ≤ 2.

[0012] Furthermore, the SiOx / C composite anode material has a particle size of 1-10 μm and a tap density ≥1.2 g / cm³.

[0013] Furthermore, the SiOx / C composite anode material has a spherical structure.

[0014] Another objective of this invention is to provide a method for preparing SiOx / C composite anode materials.

[0015] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0016] A method for preparing a SiOx / C composite anode material, comprising the following steps:

[0017] S1: Atomize the precursor containing siloxane;

[0018] S2: The precursor is activated in an inert atmosphere-protected activation reactor, and the temperature of the activation reactor is maintained between 600-800℃.

[0019] S3: The activated precursor is carried into a low-temperature reactor by a carrier gas to react and obtain a particulate product. The reactor temperature is 20-300℃.

[0020] S4: The particulate product is introduced into a high-temperature reactor and calcined at 800-1300℃ to obtain a silicon-based composite material.

[0021] Furthermore, the siloxane in step S1 includes at least one of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and polymethylsiloxane.

[0022] Furthermore, the precursor in step S1 includes a silane compound.

[0023] Furthermore, the atomization in step S1 includes one of the following methods: precursor evaporation, aerosol spraying, or ultrasonic atomization.

[0024] Further, in step S1, the mass ratio of siloxane to silane in the precursor containing siloxane is (5-30):(1-10).

[0025] Furthermore, the inert atmosphere mentioned in step S2 includes at least one of gases such as He, Ar, and N2.

[0026] Furthermore, a separation device is provided in the high-temperature reactor described in step S4. Beneficial effects

[0027] (1) In the prior art, in order to avoid the volatilization of low molecular weight components in the raw materials and reduce the yield, polysiloxanes need to be turned into solids under the action of platinum catalysts and then calcined. The resulting product is in block form and needs to be crushed before use. In this invention, the raw material gas is first atomized and then activated. Some Si-C bonds or Si-H bonds in the siloxane are broken to form active dangling Si- bonds. The activated siloxane is carried into the low temperature section by the carrier gas. The temperature decreases and the vaporized molecules condense. The Si- dangling bonds of different molecules combine with each other to form Si-Si bonds, thereby generating solid near-spherical particles that are infusible when heated and insoluble in common organic solvents. Finally, the powdered material is calcined at high temperature. It has good fluidity, high filling density, and can be used without crushing.

[0028] (2) Since thermally activated gas-phase polymerization is used, raw materials that do not contain unsaturated carbon-carbon bonds can also be used, thus the range of raw material selection is wider.

[0029] (3) Since polysiloxanes are liquid, crosslinking occurs between Si-H bonds and unsaturated carbon-carbon bonds in the polysiloxane. Gaseous saturated silane compounds are difficult to participate in the reaction, thus controlling the silicon-oxygen-carbon ratio in the product. This invention achieves control over the silicon-oxygen-carbon ratio by simultaneously activating silane compounds and siloxanes, causing the Si-H bonds of the silane compounds to break and forming active dangling Si- bonds, which participate in the subsequent formation of Si-Si bonds.

[0030] (4) By participating in the reaction with silane compounds, the ratio of silicon, oxygen and carbon in the SiOx / C composite anode material is controlled to achieve C / Si (atomic ratio) ≤2 and O / Si (x value) ≤1, which improves the specific capacity and the first charge-discharge coulombic efficiency, and enables the key indicators such as specific capacity, first coulombic efficiency and cycle stability to be balanced. Attached Figure Description

[0031] Figure 1 This is a SEM image of the SiOx / C composite anode material from Example 1.

[0032] Figure 2 This is a SEM image of the SiOx / C composite anode material from Example 2.

[0033] Figure 3 This is a SEM image of the SiOx / C composite anode material in Example 3. Detailed Implementation

[0034] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention. The invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0035] All reagents used in the following examples are commercially available.

[0036] The preparation method of the SiOx / C composite anode material in this application is as follows:

[0037] Step S1: Precursor gas atomization:

[0038] The precursor consists of siloxanes (such as at least one of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and polymethylsiloxane) and silane compounds (such as at least one of trimethylsilane and phenylsilane), wherein the silane compounds are used to regulate the SiOx / C ratio.

[0039] Atomization method: evaporation, aerosol spraying or ultrasonic atomization, with the mass fraction of precursor concentration preferably being 5%-30%.

[0040] Step S2 activation reaction:

[0041] In an inert gas (He, Ar or N2), the gas-atomized precursor is introduced into an activation reactor and activated at 600-800℃ (preferably 650-750℃) to break the Si-C / Si-H bonds and generate active dangling Si- bonds.

[0042] Step S3 Low-temperature reaction:

[0043] The carrier gas (inert gas) delivers the activated product into a low-temperature reactor (20-300℃, preferably 150-250℃), where active Si-suspended bonds combine to form Si-Si bonds, generating solid spherical particles.

[0044] Step S4: High-temperature calcination

[0045] The particles are fed into a high-temperature reactor (800-1300℃, preferably 1000-1200℃) to carbonize and form a SiOx / C composite material, and gas-solid separation is achieved through a porous ceramic separator.

[0046] In the above preparation method, to capture the particulate products in the high-temperature reactor and achieve gas-solid separation, a separation device that does not participate in the reaction is installed in the high-temperature reactor, such as porous ceramics, porous metals, or high-temperature resistant fabrics. The separation device can also maintain the pressure stability inside the high-temperature reactor.

[0047] The activation reactor, low-temperature reactor, and high-temperature reactor in this preparation method can be independent devices connected by connectors, or they can be different temperature-controlled areas arranged sequentially in one device. Example 1

[0048] A method for preparing a SiOx / C composite anode material, comprising the following steps:

[0049] (1) A precursor consisting of 25% hexamethylcyclotrisiloxane and 5% trimethylsilane was dissolved in toluene and ultrasonically atomized to form an aerosol.

[0050] (2) The gasified precursor is passed into an activation reactor under Ar atmosphere protection for activation and is treated at 700°C for 30 minutes.

[0051] (3) The activated precursor is carried into a low-temperature reactor by the carrier gas Ar to react and obtain a particulate product. The temperature of the reactor is 200℃.

[0052] (4) The particulate product was carried into a high-temperature reactor with porous ceramics by carrier gas Ar and calcined at 1100℃ for 2h. A SiOx / C composite anode material was obtained by gas-solid separation.

[0053] Testing revealed that the SiOx / C composite anode material prepared by the above method has a D50 of 3.9 μm and a tap density of 1.25 g / cm³. Example 2

[0054] A method for preparing a SiOx / C composite anode material, comprising the following steps:

[0055] (1) A precursor composed of polymethylsiloxane and trimethylsilane in a mass ratio of 30:10 is vaporized in a heated evaporator.

[0056] (2) The vaporized precursor was treated at 750°C for 20 minutes in a N2 atmosphere.

[0057] (3) The activated precursor is carried into a low-temperature reactor by carrier gas N2 to react and obtain a particulate product. The reactor temperature is 250℃.

[0058] (4) The particulate product is carried into a high-temperature reactor equipped with porous ceramics by carrier gas N2 and calcined at 1200°C for 1.5 h. A SiOx / C composite anode material is obtained by gas-solid separation.

[0059] Testing revealed that the SiOx / C composite anode material prepared by the above method has a D50 of 5.6 μm and a tap density of 1.28 g / cm³. Example 3

[0060] A method for preparing a SiOx / C composite anode material, comprising the following steps:

[0061] (1) A precursor composed of polymethylsiloxane and phenylsilane in a mass ratio of 30:10 is vaporized in a heated evaporator.

[0062] (2) The vaporized precursor was treated at 750°C for 20 minutes in a N2 atmosphere.

[0063] (3) The activated precursor is carried into a low-temperature reactor by carrier gas N2 to react and obtain a particulate product. The temperature of the reactor is 250℃.

[0064] (4) The particulate product is carried into a high-temperature reactor equipped with porous ceramics by carrier gas N2 and calcined at 1000℃ for 1.5h. A SiOx / C composite anode material is obtained by gas-solid separation.

[0065] Testing revealed that the SiOx / C composite anode material prepared by the above method has a D50 of 8.5 μm and a tap density of 1.30 g / cm³.

[0066] The battery performance was tested using the SiOx / C composite material obtained in the examples as the negative electrode, PE separator, and lithium iron phosphate positive electrode material. The results are shown in Table 1.

[0067] Table 1 Performance indicators of SiOx / C composite anode materials in the examples

[0068]

[0069] C / Si to O / Si ratio:

[0070] Examples 1-3 show that by using silicon hydride to regulate C / Si≤2 and x≤1, the excessive introduction of carbon and oxygen was significantly reduced, thereby increasing the specific capacity (1650-1780 mAh / g).

[0071] First Coulomb efficiency:

[0072] Examples 1-3 show that the spherical structure reduces side reactions, resulting in an initial efficiency of 87%-89%.

[0073] Cyclic stability:

[0074] The SiOx uniformly dispersed and carbon matrix buffered the volume expansion in Examples 1-3, and the capacity retention rate was ≥90% after 100 cycles.

[0075] Yield:

[0076] Examples 1-3 require no catalyst or pulverization step, with a yield ≥85%.

[0077] The detailed descriptions listed above are merely specific illustrations of feasible embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any obvious improvements, substitutions, or modifications that can be made by those skilled in the art without departing from the essence of the present invention are within the protection scope of the present invention.

Claims

1. A method for preparing a SiOx / C composite anode material, characterized in that... : The steps are as follows: S1: Atomize the precursor containing siloxane; S2: The precursor is activated in an inert atmosphere-protected activation reactor, and the temperature of the activation reactor is maintained between 600-800℃. S3: The activated precursor is carried into a low-temperature reactor by a carrier gas to react and obtain a particulate product. The reactor temperature is 20-300℃. S4: The particulate product is introduced into a high-temperature reactor and calcined at 800-1300℃ to obtain SiOx / C composite anode material; The siloxane in step S1 includes at least one of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and polymethylsiloxane. The precursor in step S1 includes a silane compound; The SiOx / C composite anode material in step S4 includes SiOx and a C layer coated on the surface of SiOx. The SiOx is uniformly distributed in the C layer, X < 1, and the atomic ratio of C / Si is ≤ 2.

2. The method for preparing the SiOx / C composite anode material according to claim 1, characterized in that: The atomization in step S1 includes one of the following methods: precursor evaporation, aerosol spraying, or ultrasonic atomization.

3. The method for preparing the SiOx / C composite anode material according to claim 1, characterized in that: In step S1, the mass ratio of siloxane to silane in the precursor containing siloxane is (5-30):(1-10).

4. The method for preparing the SiOx / C composite anode material according to claim 1, characterized in that: The inert atmosphere mentioned in step S2 includes at least one of He, Ar, and N2 gases.

5. The method for preparing the SiOx / C composite anode material according to claim 1, characterized in that: A separation device is installed in the high-temperature reactor described in step S4.

6. The method for preparing the SiOx / C composite anode material according to claim 1, characterized in that: The SiOx / C composite anode material described in step S4 has a particle size of 1-10 μm and a tap density ≥1.2 g / cm³.

7. The method for preparing the SiOx / C composite anode material according to claim 1 or 6, characterized in that: The SiOx / C composite anode material described in step S4 has a spherical structure.

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