SiOx / C composite negative electrode material and preparation method thereof

Abstract

The invention 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, and Xlt; the invention further discloses a preparation method of the SiOx / C composite negative electrode material, and the preparation method comprises the following steps: S1, carrying out gas atomization on a precursor containing siloxane; s2, the precursor is introduced into an activation reactor protected by inert atmosphere for activation, and the temperature of the activation reactor is kept between 600 DEG C and 800 DEG C; s3, the activated precursor is brought into a low-temperature reactor through carrier gas for a reaction, a granular product is obtained, and the temperature of the reactor is 20-300 DEG C; and S4, bringing the granular product into a high-temperature reactor, and calcining at 800-1300 DEG C to obtain the SiOx / C composite negative electrode material. The negative electrode material is large in gram capacity and high in initial charge-discharge coulombic efficiency; the method does not need to use a catalyst, the raw material source is wide, and the obtained product is powdery and does not need to be crushed.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and particularly relates to a SiOx / C composite anode material and a preparation method thereof. Background Art

[0002] With the wide application of lithium-ion batteries in fields such as electric vehicles and portable electronic devices, the performance requirements for anode materials are getting higher and higher. Due to its low theoretical specific capacity (372 mAh / g), the traditional graphite anode material is difficult to meet the requirements of high-energy-density batteries.

[0003] Silicon-based materials have become a research hotspot due to their high theoretical specific capacity (about 4200 mAh / g). However, they have serious volume expansion during charge and discharge, resulting in poor cycle stability, poor conductivity, easy reaction with electrolytes, and structural collapse due to severe volume effects during the charge and discharge cycle, which limits their practical applications. To overcome the above shortcomings, technical personnel introduce structure-stabilizing elements (such as oxygen) into silicon-based materials. However, due to the still poor conductivity of silicon-oxygen anode materials and the low Coulomb efficiency of the first charge and discharge, silicon-oxygen anode materials need to be used in combination with carbon-based anode materials such as graphite.

[0004] Currently, industrial silicon-oxygen anode materials are mainly prepared through process steps such as vapor deposition of SiO, crushing, surface carbon coating, and mixing with graphite, and a large number of protection measures need to be taken at each stage to prevent the introduction of impurities during the process and reduce the contact between SiO and oxygen and water in the air. The process is complex and lengthy.

[0005] In the article "Preparation of High-Capacity C / Si-O-C Anode Materials and Study on the Mechanism of Lithium Ion Insertion and Extraction" by Liu Xiang of National University of Defense Technology, a composite material of C / SiOx generated by pyrolysis of polysiloxane at high temperature is used as the anode material for lithium-ion batteries, which has a high specific capacity and cycle stability. Compared with the current industrial methods, the process is simple. However, this method has the following deficiencies.

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

[0007] (2) Since the product undergoing high temperature pyrolysis is silicone rubber, the product is in block form and needs to be crushed before use.

[0008] (3) Since the gram capacity of C / SiOx composite negative electrode materials is mainly contributed by the Si element, the excess carbon introduced by the unsaturated carbon-carbon bonds in the raw materials makes the carbon content of the final product too high, with an average C / Si ratio of 3.5, which limits the gram 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 pyrolysis of polysiloxane is generally greater than 1, which limits the gram capacity of C / SiOx. The excess oxygen in the material reacts with lithium ions to generate irreversible products such as Li2O, which makes the initial charge and discharge coulomb efficiency of lithium-ion batteries using C / SiOx as negative electrode materials low. Summary of the invention

[0009] The purpose of the present invention is to provide a SiOx / C composite negative electrode material and a preparation method thereof. The negative electrode material has a large gram capacity and a high first charge and discharge coulomb efficiency. The method does not require the use of a catalyst, has a wide source of raw materials, and the obtained product is in powder form and does not need to be crushed.

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

[0011] A SiOx / C composite negative electrode material comprises SiOx and a C layer coated on the surface of the SiOx, wherein the SiOx is uniformly distributed in the C, the X is less than 1, and the atomic ratio of C / Si is less than 2.

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

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

[0014] Another object of the present invention is to provide a method for preparing a SiOx / C composite negative electrode material.

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

[0016] A method for preparing a SiOx / C composite negative electrode material, the steps are as follows: S1: atomizing a precursor containing siloxane; S2: Passing the precursor into an activation reactor protected by an inert atmosphere for activation, wherein the temperature of the activation reactor is maintained between 600-800° C.; S3: The activated precursor is brought into a low-temperature reactor by a carrier gas for reaction to obtain a granular product, wherein the temperature of the reactor is 20-300° C.; S4: Bring the granular product into a high-temperature reactor and calcine it at 800-1300° C. to obtain a silicon-based composite material.

[0017] Furthermore, the siloxane in step S1 includes at least one of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and polymethylsiloxane.

[0018] Furthermore, the precursor in step S1 includes silicon hydride compounds.

[0019] Furthermore, the aerosolization in step S1 includes evaporating the precursor, aerosol spraying or ultrasonic atomization.

[0020] Furthermore, in the step S1, the mass ratio of siloxane to silicon hydride in the siloxane-containing precursor is (5-30): (1-10).

[0021] Furthermore, the inert atmosphere in step S2 includes at least one of gases such as He, Ar, and N2.

[0022] Furthermore, a separation device is provided in the high temperature reactor described in step S4. Beneficial Effects

[0023] (1) In the prior art, in order to prevent the volatilization of low molecular components in the raw materials and reduce the yield, polysiloxane needs to be solidified under the action of platinum catalyst and then calcined. The obtained product is in block form and needs to be crushed before use. The present invention first atomizes the raw gas and then activates it. Part of the Si-C bonds or Si-H bonds in the siloxane are broken to form active dangling bonds Si-. The activated siloxane is brought into the low temperature section by the carrier gas. The temperature is lowered to cause the vaporized molecules to condense. The Si-dangling bonds of different molecules combine with each other to form Si-Si bonds, thereby generating solid nearly spherical particles that are infusible when heated and insoluble in general organic solvents. Finally, it is calcined at high temperature to form a powdered material with good fluidity and high filling density. It can be used without crushing.

[0024] (2) Since thermally excited gas phase polymerization is used, raw materials that do not contain unsaturated carbon-carbon bonds can also be used, so the selection range of raw materials is wider.

[0025] (3) Since polysiloxane is in liquid state, crosslinking occurs between Si-H bonds and unsaturated carbon-carbon bonds in polysiloxane, and gaseous saturated silicon hydride compounds are difficult to participate in the reaction, thereby regulating the ratio of silicon, oxygen and carbon elements in the product. The present invention can achieve the regulation of the ratio of silicon, oxygen and carbon elements by activating silicon hydride compounds and siloxane at the same time, breaking the Si-H bonds of silicon hydride compounds and forming active dangling bonds Si-, which participate in the subsequent generation of Si-Si bonds.

[0026] (4)By involving silane compounds in the reaction, the silicon-oxygen-carbon ratio in the SiOx / C composite anode material is regulated to achieve C / Si (atomic ratio) ≤ 2 and O / Si (x value) ≤ 1, improving the specific capacity and the Coulombic efficiency of the first charge and discharge, and enabling a balance among key indicators such as specific capacity, first Coulombic efficiency, and cycle stability. Description of the Drawings

[0027] Figure 1 It is the SEM image of the SiOx / C composite anode material of Example 1.

[0028] Figure 2 It is the SEM image of the SiOx / C composite anode material of Example 2.

[0029] Figure 3 It is the SEM image of the SiOx / C composite anode material of Example 3. Detailed Embodiments

[0030] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. The preferred embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of the present invention more thorough and comprehensive. The present invention will be further described below in conjunction with the drawings and specific embodiments.

[0031] The reagents used in the following embodiments are all commercially available.

[0032] The preparation method of the SiOx / C composite anode material in this application is as follows: Step S1 Precursor Gas Atomization: Precursor Composition: Siloxane (such as at least one of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, polymethylsiloxane) and silane compound (such as at least one of trimethylsilane, phenylsilane), wherein the silane compound is used to regulate the SiOx / C ratio.

[0033] Gas Atomization Method: Evaporation, aerosol spray or ultrasonic atomization, and the mass fraction of the precursor concentration is preferably 5% - 30%.

[0034] Step S2 Activation Reaction: In an inert gas (He, Ar or N2), the gas-atomized precursor is introduced into an activation reactor and activated at 600 - 800 °C (preferably 650 - 750 °C) to break the Si-C / Si-H bonds to generate active dangling bonds Si-.

[0035] Step S3 Low-Temperature Reaction: The carrier gas (inert gas) feeds the activation product into a low-temperature reactor (20 - 300 °C, preferably 150 - 250 °C), where the active Si - dangling bonds combine to form Si - Si bonds, generating solid spherical-like particles.

[0036] Step S4: High-temperature calcination: The particles are fed into a high-temperature reactor (800 - 1300 °C, preferably 1000 - 1200 °C), carbonized to form a SiOx / C composite material, and gas - solid separation is achieved through a porous ceramic separator.

[0037] In the above preparation method, in order to capture the particulate product in the high - temperature reactor and achieve gas - solid separation, a separation device that does not participate in the reaction, such as porous ceramics, porous metals, heat - resistant fabrics, etc., is provided in the high - temperature reactor. The separation device can also maintain the pressure stability in the high - temperature reactor.

[0038] The activation reactor, low - temperature reactor, and high - temperature reactor in this preparation method can be independent devices connected by connectors, or different independently temperature - controllable regions sequentially arranged in one device. Example 1

[0039] A preparation method of a SiOx / C composite anode material is as follows: (1) A precursor composed of hexamethylcyclotrisiloxane with a concentration of 25% + trimethylsilane with a concentration of 5% is dissolved in toluene and ultrasonically atomized to form an aerosol.

[0040] (2) The vaporized precursor is introduced into an activation reactor protected by an Ar atmosphere for activation and maintained at 700 °C for 30 minutes.

[0041] (3) The activated precursor is carried into a low - temperature reactor by the carrier gas Ar for reaction to obtain a particulate product, and the temperature of this reactor is 200 °C.

[0042] (4) The particulate product is carried into a high - temperature reactor equipped with porous ceramics by the carrier gas Ar, calcined at 1100 °C for 2 h, and through gas - solid separation, a SiOx / C composite anode material is obtained.

[0043] After testing, the D50 of the SiOx / C composite anode material obtained by the above preparation method is 3.9 μm, and the tap density is 1.25 g / cm³. Example 2

[0044] A preparation method of a SiOx / C composite anode material is as follows: (1) A precursor composed of polymethylsiloxane and trimethylsilane with a mass ratio of 30:10 is vaporized in a heating evaporator.

[0045] (2) The gasified precursor was treated at 750 °C for 20 minutes in an N2 atmosphere.

[0046] (3) The activated precursor was introduced into a low-temperature reactor by carrier gas N2 for reaction to obtain a granular product, and the temperature of this reactor was 250 °C.

[0047] (4) The granular product was introduced into a high-temperature reactor equipped with porous ceramics by carrier gas N2 and calcined at 1200 °C for 1.5 h. Through gas-solid separation, a SiOx / C composite anode material was obtained.

[0048] After testing, the D50 of the SiOx / C composite anode material obtained by the above preparation method was 5.6 μm, and the tap density was 1.28 g / cm³. Example 3

[0049] A preparation method of a SiOx / C composite anode material is as follows: (1) A precursor composed of polymethylsiloxane and phenylsilane with a mass ratio of 30:10 was gasified in a heating evaporator.

[0050] (2) The gasified precursor was treated at 750 °C for 20 minutes in an N2 atmosphere.

[0051] (3) The activated precursor was introduced into a low-temperature reactor by carrier gas N2 for reaction to obtain a granular product, and the temperature of this reactor was 250 °C.

[0052] (4) The granular product was introduced into a high-temperature reactor equipped with porous ceramics by carrier gas N2 and calcined at 1000 °C for 1.5 h. Through gas-solid separation, a SiOx / C composite anode material was obtained.

[0053] After testing, the D50 of the SiOx / C composite anode material obtained by the above preparation method was 8.5 μm, and the tap density was 1.30 g / cm³.

[0054] Using the SiOx / C composite material obtained in the example as the anode, a PE separator, and a lithium iron phosphate cathode material to form a battery to test the performance, as shown in Table 1.

[0055] Table 1 Performance indicators of the SiOx / C composite anode material in the example

[0056] C / Si and O / Si ratios: In Examples 1-3, through the regulation of silanes, C / Si ≤ 2, x ≤ 1, significantly reducing the excessive introduction of carbon and oxygen, and improving the specific capacity (1650 - 1780 mAh / g).

[0057] Initial Coulombic efficiency: Examples 1-3 reduce side reactions due to the spheroid-like structure, with the initial efficiency reaching 87%-89%.

[0058] Cyclic stability: The SiOx of Examples 1-3 is uniformly dispersed and the carbon matrix buffers volume expansion, with the capacity retention rate ≥ 90% after 100 cycles.

[0059] Yield: Examples 1-3 do not require a catalyst and a crushing step, with the yield ≥ 85%.

[0060] The series of detailed descriptions listed above are only specific descriptions of the feasible embodiments of the present invention, but the present invention is not limited to the above embodiments. Without departing from the essence of the present invention, any obvious improvements, substitutions or variations that those skilled in the art can make all fall within the protection scope of the present invention.

Claims

1. A SiOx / C composite negative electrode material, characterized in that: It comprises SiOx and a C layer coated on the surface of SiOx, wherein 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.

2. The SiOx / C composite negative electrode material according to claim 1, characterized in that: The SiOx / C composite negative electrode material has a particle size of 1-10 μm and a tap density of ≥1.2 g / cm³.

3. The SiOx / C composite negative electrode material according to claim 1 or 2, characterized in that: The SiOx / C composite negative electrode material has a spherical structure.

4. A method for preparing a SiOx / C composite negative electrode material, characterized in that : Here are the steps: S1: atomizing a precursor containing siloxane; S2: Passing the precursor into an activation reactor protected by an inert atmosphere for activation, wherein the temperature of the activation reactor is maintained between 600-800° C.; S3: The activated precursor is brought into a low-temperature reactor by a carrier gas for reaction to obtain a granular product, wherein the temperature of the reactor is 20-300° C.; S4: Bring the granular product into a high-temperature reactor and calcine it at 800-1300° C. to obtain a silicon-based composite material.

5. The method for preparing the SiOx / C composite negative electrode material according to claim 4, characterized in that: The siloxane in step S1 includes at least one of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and polymethylsiloxane.

6. The method for preparing the SiOx / C composite negative electrode material according to claim 4 or 5, characterized in that: The precursor in step 1 includes silicon hydride compounds.

7. The method for preparing the SiOx / C composite negative electrode material according to claim 4, characterized in that: The aerosolization in step S1 includes evaporating the precursor, aerosol spraying or ultrasonic atomization.

8. The method for preparing the SiOx / C composite negative electrode material according to claim 6, characterized in that: The mass ratio of siloxane to silicon hydride in the siloxane-containing precursor in step S1 is (5-30): (1-10).

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

10. The method for preparing the SiOx / C composite negative electrode material according to claim 4, characterized in that: A separation device is provided in the high temperature reactor described in step S4.

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