Silicon-carbon composite material with three-dimensional porous structure as well as preparation method and application of silicon-carbon composite material

Abstract

The invention relates to a silicon-carbon composite material with a three-dimensional porous structure as well as a preparation method and application thereof, and belongs to the technical field of preparation methods of battery materials. Comprising the following steps: (1) carrying out hydrothermal in-situ coating by taking silicon dioxide as a silicon source, organic polymer resin as a carbon source and a nitrogen-containing organic matter as a nitrogen source, and carrying out solid-liquid separation to obtain a nitrogen-doped polymer resin coated silicon dioxide composite material; and (2) mixing the nitrogen-doped polymer resin coated silicon dioxide composite material obtained in the step (1) with a metal hydride reducing agent, heating to 500-800 DEG C in an inert atmosphere, carrying out high-temperature heat treatment, washing, and drying to obtain the silicon-carbon composite material. According to the invention, a solid-phase one-step reduction carbonization process is adopted to prepare a stable hierarchical porous structure compared with first reduction and then coating carbonization, and the cycle performance of the material is effectively improved.

Description

Technical Field

[0001] The present invention relates to a three-dimensional porous silicon-carbon composite material and a preparation method and application thereof, belonging to the technical field of battery material preparation methods. Background Art

[0002] Lithium-ion batteries, due to their green, high-energy, high energy density, excellent cycle performance, and environmentally friendly advantages, are widely used in products such as mobile communications, laptops, and new energy electric vehicles. In recent years, with the rapid development of the new energy vehicle industry, the demand for high-energy-density batteries has been increasing year by year, and the demand for lithium-ion battery anode materials has also been growing. While traditional graphite anode materials offer excellent cycle performance and high theoretical specific capacity, their actual specific capacity is low, making them unable to meet the high-energy-density battery requirements of new energy vehicles. Therefore, the development of new high-specific-capacity anode materials has become a key research area for lithium-ion batteries.

[0003] Among the many negative electrode materials, silicon is considered to be a very ideal negative electrode material for the next generation of lithium-ion batteries due to its high lithium storage capacity (4200mAh / g), relatively low voltage platform (~0.4V vs Li+ / Li), extremely abundant reserves in the earth's crust, environmental friendliness and chemical stability. However, silicon negative electrode materials have a huge volume expansion (>300%) during the alloying process, which will cause the active material on the electrode sheet to pulverize and fall off, resulting in rapid capacity decay, thus hindering its industrial application process. In addition, since silicon is an intrinsic semiconductor material, its electronic conductivity is poor, which is not conducive to the rapid transmission of electrons on the electrode sheet, affecting the normal performance of the silicon-based material capacity, resulting in poor rate performance of silicon negative electrode materials.

[0004] To solve the above-mentioned problems of silicon negative electrodes, one of the most effective methods is to prepare porous silicon-carbon composite materials. Silicon can be used as an active material to provide capacity, and its porous structure is conducive to maintaining structural stability. The carbon in the composite material usually acts as a coating layer, which improves the conductivity of the material while slowing down the volume expansion of silicon. The traditional preparation process mainly uses inorganic acid as an etchant to etch silicon-based alloys to obtain porous silicon materials. However, its large-scale production and commercial application are seriously limited by problems such as poor safety, high environmental pollution and high production costs.

[0005] A Chinese invention patent, published on January 22, 2014, with publication number CN103531760A, discloses a yolk-eggshell structured porous silicon-carbon composite microsphere and a method for preparing the same. Specifically, the invention discloses using silicon dioxide as a silicon source, converting it into porous silicon using magnesium thermal reduction, and using a strong base to assist in regulating the pore structure of the composite material. The advantages of this method are low raw material costs and a simple method for controlling the material structure. However, because the material has a large specific surface area, the initial coulombic efficiency is low, and the relatively complex carbon coating process involved in the early stages is not conducive to industrial production. Furthermore, the generation of the byproduct SiC is difficult to control during the magnesium thermal reduction process, which affects the performance of the composite material.

[0006] The Chinese invention patent with the announcement date of May 25, 2021 and the announcement number CN111082013B discloses a preparation method of a carbon-coated nitrogen-magnesium-doped porous silicon-based composite material and a lithium-ion battery. It specifically discloses that a carbon source solution is added dropwise to nano-silica powder, and then a high-temperature carbonization operation is performed under a nitrogen atmosphere to obtain a carbon-coated nitrogen-doped silica material; the carbon-coated nitrogen-doped silica material is subjected to a high-temperature reduction operation under a reducing atmosphere to obtain a carbon-coated nitrogen-doped silicon-based composite material; the carbon-coated nitrogen-doped silicon-based composite material is etched to obtain a carbon-coated nitrogen-doped porous silicon-based composite material; the carbon-coated nitrogen-doped porous silicon-based composite material is ultrasonically dispersed to obtain a dispersed mixed turbid liquid; the dispersed mixed turbid liquid is added to the magnesium source mixed solution, and then separated, washed and dried to obtain a carbon-coated nitrogen-magnesium-doped porous silicon-based composite material. This method can effectively suppress the volume expansion of silicon and effectively improve the conductivity and initial efficiency of silicon-carbon materials. However, this method has the problems of complex preparation process, high energy consumption, complex equipment and difficulty in large-scale production. Summary of the Invention

[0007] The first object of the present invention is to provide a method for preparing a three-dimensional porous silicon-carbon composite material to solve the problems of complex process and high energy consumption in the prior art preparation method of porous silicon-carbon composite materials.

[0008] The second object of the present invention is to provide a three-dimensional porous silicon-carbon composite material, and to provide a porous silicon-carbon composite material with good cycle stability and high first coulombic efficiency.

[0009] The third object of the present invention is to provide a three-dimensional porous structure of silicon-carbon composite material for use in lithium batteries, providing a negative electrode material for lithium-ion batteries with good cycle stability and high first coulombic efficiency.

[0010] In order to achieve the above-mentioned object, the technical solution of the method for preparing a three-dimensional porous silicon-carbon composite material in the present invention is:

[0011] A method for preparing a three-dimensional porous silicon-carbon composite material comprises the following steps:

[0012] (1) Using silica as a silicon source, an organic polymer resin as a carbon source, and a nitrogen-containing organic matter as a nitrogen source, hydrothermal in-situ coating is performed, and after solid-liquid separation, a nitrogen-doped polymer resin-coated silica composite material is obtained;

[0013] (2) The nitrogen-doped polymer resin-coated silica composite material obtained in step (1) is mixed with a metal hydride reducing agent, and then heated to 500-800° C. in an inert atmosphere for high-temperature heat treatment, and then washed and dried to obtain a silicon-carbon composite material.

[0014] The beneficial effect of the above technical solution is that: the present invention uses nano-silica as a silicon source, an organic polymer resin as a carbon source, and a nitrogen-containing organic matter as a nitrogen source, and prepares a nitrogen-doped polymer resin-coated silica composite material by a hydrothermal method, and then uses the strong reducing property of a strong reducing agent to reduce the silica in the composite material to silicon. Moreover, during the reduction process, the organic carbon on the surface of the composite material is also cracked due to heating, thereby forming a nitrogen-doped thermal cracking carbon coating layer on the surface of the porous silicon, thereby enhancing the conductivity and stability of the material, forming a synergistic effect with the porous silicon material, and further improving the electrochemical properties of the silicon-carbon composite material.

[0015] Furthermore, the present invention utilizes a solid-phase one-step reduction carbonization process, selects the aforementioned reducing agent, and utilizes its strong reducing properties to achieve a one-step preparation of porous silicon. Furthermore, the preparation process produces only metaaluminates or alkaline earth metal oxides, which are easily removable byproducts. The final product is environmentally friendly, has a simple processing process, and does not pollute the environment. Furthermore, the preparation method of the present invention has low energy consumption, a simple and controllable process flow, and low equipment costs, making it easy to implement large-scale production.

[0016] The mechanism of the one-step reduction carbonization method using a strong reducing agent in the present invention is as follows (explained using MgH2 as an example):

[0017] 2MgH2(s)+SiO2(s)=2MgO(s)+Si(s)+2H2(g);

[0018] The present invention uses a metal hydride with strong reducing properties to reduce SiO2, achieving efficient reduction at a relatively low temperature and avoiding the energy consumption and equipment requirements caused by high temperatures. Through thermodynamic calculations, the reaction temperature is between 500 and 800°C, the ΔG value is less than 0, and is between -317.86kJ / mol and -374.60kJ / mol. At a temperature of 500 to 800°C, the organic carbon coated on the surface of the nitrogen-doped polymer resin-coated silica composite material is carbonized to obtain carbon, but under these reaction conditions, the reaction Si(s)+C(s)=SiC(s) is difficult to occur. Therefore, the carbon protective layer on the silica surface will not further generate silicon carbide with the generated porous silicon, which is conducive to the stable formation of the porous silicon-carbon composite material.

[0019] On the other hand, gases are generated in the above reaction, and these gases escape during the carbonization of the polymer resin to form a rich porous three-dimensional structure, which helps to alleviate the volume expansion of the silicon-carbon composite material obtained by the present invention when used as a battery negative electrode material.

[0020] Furthermore, before the reduction carbonization treatment, a layer of deoxidizer is spread on the surface of the mixture obtained by mixing the nitrogen-doped polymer resin-coated silica composite material and the metal hydride reducing agent; preferably, the deoxidizer is foamed titanium; further preferably, the particle size of the foamed titanium is 50-100 μm.

[0021] As a further improvement, the metal hydride reducing agent in step (2) is one of KH, NaH, CaH2, LiH, MgH2, LiAlH4, and NaAlH4; and the mass ratio of the metal hydride reducing agent to the nitrogen-doped polymer resin-coated silica composite material is (2 to 6): (1 to 1.5).

[0022] As a further improvement, the high temperature heat treatment time in step (2) is 4 to 8 hours.

[0023] Furthermore, the present invention can precisely control the reaction degree of silicon dioxide in the composite material by controlling the amount of the strong reducing agent, the reaction temperature and the reaction time.

[0024] As a further improvement, the organic polymer resin in step (1) is one or more of resorcinol formaldehyde resin, melamine resin, urea-formaldehyde resin, epoxy resin, acrylic resin, polyether polyester resin, furfural resin, and polyamide resin; and the nitrogen-containing organic matter is one or more of melamine polyphosphate, melamine, acrylonitrile, urea, and thiourea.

[0025] As a further improvement, the mass ratio of the silicon dioxide, the organic polymer resin and the nitrogen-containing organic matter in step (1) is (2-6): (3-5): (1-2.5).

[0026] As a further improvement, the hydrothermal in-situ coating in step (1) is carried out at 60-240° C. for 2-4 hours.

[0027] As a further improvement, the particle size of the silicon dioxide is 0.1 μm-30 μm.

[0028] As a further improvement, the washing includes pickling to remove by-products of the high temperature heat treatment.

[0029] In order to achieve the above-mentioned object, the technical solution of the three-dimensional porous silicon-carbon composite material prepared by the method for preparing the three-dimensional porous silicon-carbon composite material in the present invention is:

[0030] A method for preparing a silicon-carbon composite material with a three-dimensional porous structure.

[0031] The beneficial effect of the above technical solution is that the surface of the three-dimensional porous silicon-carbon composite material of the present invention is doped with nitrogen atoms, which introduces more active sites, improves the electronic conductivity of the silicon-carbon composite material, and can enhance the structural stability of the material, thereby reducing the material disintegration or pulverization caused by volume changes during the charge and discharge process of the composite material.

[0032] Furthermore, the three-dimensional porous silicon-carbon composite material prepared by the present invention has a porous structure, which is conducive to alleviating the volume expansion of the material during charging and discharging, and improving the cycle performance of the composite material; the outer layer of nitrogen-doped pyrolytic carbon can effectively enhance the overall electrical conductivity of the material, and the rate performance can be further improved.

[0033] In order to achieve the above-mentioned purpose, the technical solution of the application of the three-dimensional porous silicon-carbon composite material in lithium batteries of the present invention is:

[0034] Application of a three-dimensional porous silicon-carbon composite material in lithium batteries.

[0035] The beneficial effect of the above technical solution is that: the present invention uses the prepared three-dimensional porous structure silicon-carbon composite material as the negative electrode material to prepare a lithium battery, and the lithium battery has good cycle performance and high capacity retention rate.

[0036] Specifically, a three-dimensional porous silicon-carbon composite material is used as the negative electrode material of a lithium battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a SEM image (1 μm) of the silicon-carbon composite material prepared in Example 2 of the present invention;

[0038] Figure 2 This is a SEM image (500 nm) of the silicon-carbon composite material prepared in Example 2 of the present invention;

[0039] Figure 3 This is a charge and discharge curve diagram of a battery prepared using the silicon-carbon composite material of Example 4 in Experimental Example 1 of the present invention. DETAILED DESCRIPTION

[0040] Existing techniques primarily use inorganic acids as etchants to etch silicon-based alloys, resulting in porous silicon materials. However, these methods are severely limited in scale production and commercial application due to issues such as poor safety, significant environmental pollution, and high production costs. Furthermore, reduction and carbonization are typically performed in two separate steps, and the high temperatures used for carbonization or reduction make it difficult to control the formation of the SiC byproduct, which can affect the material's performance.

[0041] The present invention uses nano-silica as a silicon source, an organic polymer resin as a carbon source, and a nitrogen-containing organic compound as a nitrogen source to prepare a nitrogen-doped polymer resin-coated silica composite material through a hydrothermal method. The nitrogen-doped polymer resin-coated silica composite material is then carbonized and reduced using a strong reducing agent at a relatively low temperature in a one-step process to prepare a three-dimensional porous silicon-carbon composite material. The present invention employs a solid-phase one-step reduction-carbonization process. The strong reducing agent's reducing power promotes the cracking of organic carbon, thereby forming a nitrogen-doped pyrolytic carbon coating on the porous silicon surface. This enhances the material's conductivity and stability, creating a synergistic effect with the porous silicon material and further improving the composite material's electrochemical performance.

[0042] The present invention will be further described below in conjunction with specific embodiments. It should be noted that, unless otherwise specified, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments. The equipment and raw materials used are all commercially available or commonly used in the art. The methods in the following embodiments are all conventional methods in the art unless otherwise specified.

[0043] 1. Specific embodiments of a three-dimensional porous silicon-carbon composite material and its preparation method of the present invention:

[0044] Example 1

[0045] The method for preparing the three-dimensional porous silicon-carbon composite material of this embodiment comprises the following steps:

[0046] 1. Preparation of polymer resin-coated silica

[0047] 2 g of silica powder, 3 g of melamine resin, and 1 g of melamine polyphosphate were weighed and dissolved in 100 mL of deionized water. After ultrasonic dispersion, a mixed suspension was obtained. The suspension was transferred to a 200 mL hydrothermal reactor and kept at 60°C for 2 h to obtain a mixture solution. Subsequently, the mixed solution was naturally cooled to room temperature, centrifuged, washed, and dried to obtain a nitrogen-doped polymer resin-coated silica solid composite material for standby use.

[0048] 2. Preparation of three-dimensional porous silicon-carbon composite materials

[0049] (1) mechanically mixing the strong reducing agent MgH2 and the nitrogen-doped resin carbon-coated silica solid composite material obtained above at a mass ratio of 2:1 to obtain a mixture;

[0050] (2) Place the above mixture into a tube furnace and evenly spread a layer of titanium foam (m 混合物 :m 泡沫钛 =1:0.05), under the protection of argon atmosphere, the temperature was raised to 500℃ at a heating rate of 5℃ / min for high-temperature heat treatment for 4h, and then naturally cooled to room temperature; the obtained silicon-carbon composite material was placed in a prepared dilute hydrochloric acid (2mol / L) solution and soaked for 10min to remove metal oxides, and then washed three times by alternating centrifugation with deionized water and anhydrous ethanol, placed in a vacuum drying oven at a temperature of 100℃ for 3h, and after simple grinding through a 325-mesh sieve, finally, a silicon-carbon composite material with a three-dimensional porous structure was obtained.

[0051] Example 2

[0052] The method for preparing the three-dimensional porous silicon-carbon composite material of this embodiment comprises the following steps:

[0053] 1. Preparation of polymer resin-coated silica

[0054] 4 g of silica powder, 4 g of furfural resin, and 1.75 g of melamine polyphosphate were weighed and dissolved in 100 mL of deionized water. After ultrasonic dispersion, a mixed suspension was obtained. The suspension was transferred to a 200 mL hydrothermal reactor and kept at 150° C. for 3 h to obtain a mixture solution. The mixed solution was then naturally cooled to room temperature, centrifuged, washed, and dried to obtain a nitrogen-doped polymer resin-coated silica solid composite material for later use.

[0055] 2. Preparation of three-dimensional porous silicon-carbon composite materials

[0056] (1) mechanically mixing the strong reducing agent MgH2 and the nitrogen-doped resin carbon-coated silica solid composite material obtained above at a mass ratio of 4:1.25 to obtain a mixture;

[0057] (2) Place the above mixture into a tube furnace and evenly spread a layer of titanium foam (m 混合物 :m 泡沫钛=1:0.05), under the protection of argon atmosphere, the temperature was raised to 650℃ at a heating rate of 5℃ / min for high-temperature heat treatment for 6h, and then naturally cooled to room temperature; the obtained silicon-carbon composite material was placed in a prepared dilute hydrochloric acid (2mol / L) solution and soaked for 10min to remove metal oxides, and then washed three times by alternating centrifugation with deionized water and anhydrous ethanol, placed in a vacuum drying oven at a temperature of 100℃ for 3h, and after simple grinding through a 325-mesh sieve, finally, a silicon-carbon composite material with a three-dimensional porous structure was obtained.

[0058] The morphology of the three-dimensional porous silicon-carbon composite material prepared in this embodiment is as follows: Figure 1 and Figure 2 As shown in the figure, it can be seen that the composite material presents a three-dimensional spherical structure with a mostly porous structure inside.

[0059] Example 3

[0060] The method for preparing the three-dimensional porous silicon-carbon composite material of this embodiment comprises the following steps:

[0061] 1. Preparation of polymer resin-coated silica

[0062] 6 g of silica powder, 5 g of resorcinol-formaldehyde resin, and 2.5 g of melamine were weighed and dissolved in 100 mL of deionized water and uniformly dispersed by ultrasonication to obtain a mixed suspension. The suspension was transferred to a 200 mL hydrothermal reactor and kept at 240° C. for 4 h to obtain a mixture solution. The mixed solution was then naturally cooled to room temperature, centrifuged, washed, and dried to obtain a nitrogen-doped polymer resin-coated silica solid composite material for later use.

[0063] 2. Preparation of three-dimensional porous silicon-carbon composite materials

[0064] (1) mechanically mixing the strong reducing agent MgH2 and the nitrogen-doped resin carbon-coated silica solid composite material obtained above at a mass ratio of 6:1.5 to obtain a mixture;

[0065] (2) Place the above mixture into a tube furnace and evenly spread a layer of titanium foam (m mixture: m titanium foam m 混合物 :m 泡沫钛 =1:0.05), under the protection of argon atmosphere, the temperature was raised to 800℃ at a heating rate of 5℃ / min for high-temperature heat treatment for 8h, and then naturally cooled to room temperature; the obtained silicon-carbon composite material was placed in a prepared dilute hydrochloric acid (2mol / L) solution and soaked for 10min to remove metal oxides, and then washed three times by alternating centrifugation with deionized water and anhydrous ethanol, placed in a vacuum drying oven at a temperature of 100℃ for 3h, and after simple grinding through a 325-mesh sieve, finally, a silicon-carbon composite material with a three-dimensional porous structure was obtained.

[0066] Example 4

[0067] The method for preparing the three-dimensional porous silicon-carbon composite material of this embodiment comprises the following steps:

[0068] 1. Preparation of polymer resin-coated silica

[0069] 2 g of silica powder, 3 g of resorcinol formaldehyde resin, and 1 g of melamine were weighed and dissolved in 100 mL of deionized water and uniformly dispersed by ultrasonication to obtain a mixed suspension. The suspension was transferred to a 200 mL hydrothermal reactor and kept warm at 150°C for 3 h to obtain a mixture solution. The mixed solution was then naturally cooled to room temperature, centrifuged, washed, and dried to obtain a nitrogen-doped polymer resin-coated silica solid composite material for later use.

[0070] 2. Preparation of three-dimensional porous silicon-carbon composite materials

[0071] (1) mechanically mixing the strong reducing agent NaAlH4 and the nitrogen-doped resin carbon-coated silica solid composite material obtained above at a mass ratio of 2:1 to obtain a mixture;

[0072] (2) Place the above mixture into a tube furnace and evenly spread a layer of titanium foam (m 混合物 :m 泡沫钛 =1:0.05), under the protection of argon atmosphere, the temperature was raised to 650℃ at a heating rate of 5℃ / min for high-temperature heat treatment for 6h, and then naturally cooled to room temperature; the obtained silicon-carbon composite material was placed in a prepared dilute hydrochloric acid (2mol / L) solution and soaked for 10min to remove the aluminate, and then washed three times by alternating centrifugation with deionized water and anhydrous ethanol, placed in a vacuum drying oven at a temperature of 100℃ for 3h, and after simple grinding through a 325-mesh sieve, finally, a silicon-carbon composite material with a three-dimensional porous structure was obtained.

[0073] Example 5

[0074] The method for preparing the three-dimensional porous silicon-carbon composite material of this embodiment comprises the following steps:

[0075] 1. Preparation of polymer resin-coated silica

[0076] 2 g of silica powder, 3 g of epoxy resin, and 1 g of melamine polyphosphate were weighed and dissolved in 100 mL of deionized water. After ultrasonic dispersion, a mixed suspension was obtained. The suspension was transferred to a 200 mL hydrothermal reactor and kept at 150°C for 3 h to obtain a mixture solution. The mixed solution was then naturally cooled to room temperature, centrifuged, washed, and dried to obtain a nitrogen-doped polymer resin-coated silica solid composite material for later use.

[0077] 2. Preparation of three-dimensional porous silicon-carbon composite materials

[0078] (1) mechanically mixing the strong reducing agent LiAlH4 and the nitrogen-doped resin carbon-coated silica solid composite material obtained above at a mass ratio of 2:1 to obtain a mixture;

[0079] (2) Place the above mixture into a tube furnace and evenly spread a layer of titanium foam (m 混合物 :m 泡沫钛 =1:0.05), under the protection of argon atmosphere, the temperature was raised to 500℃ at a heating rate of 5℃ / min for high-temperature heat treatment for 4h, and then naturally cooled to room temperature; the obtained silicon-carbon composite material was placed in a prepared dilute hydrochloric acid (2mol / L) solution and soaked for 10min to remove the aluminate, and then washed three times by alternating centrifugation with deionized water and anhydrous ethanol, placed in a vacuum drying oven at a temperature of 100℃ for 3h, and after simple grinding through a 325-mesh sieve, finally, a silicon-carbon composite material with a three-dimensional porous structure was obtained.

[0080] Example 6

[0081] The method for preparing the three-dimensional porous silicon-carbon composite material of this embodiment comprises the following steps:

[0082] 1. Preparation of polymer resin-coated silica

[0083] 2 g of silica powder, 3 g of melamine resin, and 1 g of melamine polyphosphate were weighed and dissolved in 100 mL of deionized water. After ultrasonic dispersion, a mixed suspension was obtained. The suspension was transferred to a 200 mL hydrothermal reactor and kept at 150° C. for 3 h to obtain a mixture solution. Subsequently, the mixed solution was naturally cooled to room temperature, centrifuged, washed, and dried to obtain a nitrogen-doped polymer resin-coated silica solid composite material for standby use.

[0084] 2. Preparation of three-dimensional porous silicon-carbon composite materials

[0085] (1) mechanically mixing the strong reducing agent CaH2 and the nitrogen-doped resin carbon-coated silica solid composite material obtained above at a mass ratio of 2:1 to obtain a mixture;

[0086] (2) Place the above mixture into a tube furnace and evenly spread a layer of titanium foam (m 混合物 :m 泡沫钛=1:0.05), under the protection of argon atmosphere, the temperature was raised to 650℃ at a heating rate of 5℃ / min for high-temperature heat treatment for 6h, and then naturally cooled to room temperature; the obtained silicon-carbon composite material was placed in a prepared dilute hydrochloric acid (2mol / L) solution and soaked for 10min to remove metal oxides, and then washed three times by alternating centrifugation with deionized water and anhydrous ethanol, placed in a vacuum drying oven at a temperature of 100℃ for 3h, and after simple grinding through a 325-mesh sieve, finally, a silicon-carbon composite material with a three-dimensional porous structure was obtained.

[0087] Example 7

[0088] The method for preparing the three-dimensional porous silicon-carbon composite material of this embodiment comprises the following steps:

[0089] 1. Preparation of polymer resin-coated silica

[0090] 2 g of silica powder, 3 g of melamine resin, and 1 g of melamine polyphosphate were weighed and dissolved in 100 mL of deionized water. After ultrasonic dispersion, a mixed suspension was obtained. The suspension was transferred to a 200 mL hydrothermal reactor and kept at 150° C. for 3 h to obtain a mixture solution. Subsequently, the mixed solution was naturally cooled to room temperature, centrifuged, washed, and dried to obtain a nitrogen-doped polymer resin-coated silica solid composite material for standby use.

[0091] 2. Preparation of three-dimensional porous silicon-carbon composite materials

[0092] (1) mechanically mixing the strong reducing agent NaH and the nitrogen-doped resin carbon-coated silica solid composite material obtained above at a mass ratio of 2:1 to obtain a mixture;

[0093] (2) Place the above mixture into a tube furnace and evenly spread a layer of titanium foam (m 混合物 :m 泡沫钛 =1:0.05), under the protection of argon atmosphere, the temperature was raised to 650℃ at a heating rate of 5℃ / min for high-temperature heat treatment for 6h, and then naturally cooled to room temperature; the obtained silicon-carbon composite material was placed in a prepared dilute hydrochloric acid (2mol / L) solution and soaked for 10min to remove metal oxides, and then washed three times by alternating centrifugation with deionized water and anhydrous ethanol, placed in a vacuum drying oven at a temperature of 100℃ for 3h, and after simple grinding through a 325-mesh sieve, finally, a silicon-carbon composite material with a three-dimensional porous structure was obtained.

[0094] Example 8

[0095] The method for preparing the three-dimensional porous silicon-carbon composite material of this embodiment comprises the following steps:

[0096] 1. Preparation of polymer resin-coated silica

[0097] 2 g of silica powder, 3 g of melamine resin, and 1 g of melamine polyphosphate were weighed and dissolved in 100 mL of deionized water. After ultrasonic dispersion, a mixed suspension was obtained. The suspension was transferred to a 200 mL hydrothermal reactor and kept at 150° C. for 3 h to obtain a mixture solution. Subsequently, the mixed solution was naturally cooled to room temperature, centrifuged, washed, and dried to obtain a nitrogen-doped polymer resin-coated silica solid composite material for standby use.

[0098] 2. Preparation of three-dimensional porous silicon-carbon composite materials

[0099] (1) mechanically mixing the strong reducing agent LiH and the nitrogen-doped resin carbon-coated silica solid composite material obtained above at a mass ratio of 2:1 to obtain a mixture;

[0100] (2) Place the above mixture into a tube furnace and evenly spread a layer of titanium foam (m 混合物 :m 泡沫钛 =1:0.05), under the protection of argon atmosphere, the temperature was raised to 650℃ at a heating rate of 5℃ / min for high-temperature heat treatment for 6h, and then naturally cooled to room temperature; the obtained silicon-carbon composite material was placed in a prepared dilute hydrochloric acid (2mol / L) solution and soaked for 10min to remove metal oxides, and then washed three times by alternating centrifugation with deionized water and anhydrous ethanol, placed in a vacuum drying oven at a temperature of 100℃ for 3h, and after simple grinding through a 325-mesh sieve, finally, a silicon-carbon composite material with a three-dimensional porous structure was obtained.

[0101] 2. Comparative Example

[0102] Comparative Example 1

[0103] The preparation method of the silicon-carbon composite negative electrode material of this comparative example is as follows:

[0104] 1. Preparation of three-dimensional porous silicon

[0105] (1) Mechanically mix the strong reducing agent MgH2 and silicon dioxide powder in a mass ratio of 2:1 to obtain a mixture for standby use.

[0106] (2) Place the above mixture into a tube furnace and evenly spread a layer of titanium foam (m 混合物 :m 泡沫钛=1:0.05), under the protection of argon atmosphere, the temperature was raised to 650℃ at a heating rate of 5℃ / min for high-temperature heat treatment for 6h, and then naturally cooled to room temperature; the obtained solid material was placed in a prepared dilute hydrochloric acid (2mol / L) solution and soaked for 10min to remove metal oxides, and then washed three times by alternating centrifugation with deionized water and anhydrous ethanol, placed in a vacuum drying oven at a temperature of 100℃ for 3h, and after simple grinding and passing through a 325-mesh sieve, finally, a three-dimensional porous silicon negative electrode material was obtained.

[0107] 2. Preparation of polymer resin-coated porous silicon

[0108] 2 g of porous silicon powder, 3 g of resorcinol formaldehyde resin, and 1 g of melamine polyphosphate were weighed and dissolved in 100 mL of deionized water. After ultrasonic dispersion, a mixed suspension was obtained. The suspension was transferred to a 200 mL hydrothermal reactor and kept at 150 ° C for 3 h to obtain a mixture solution. Then, the mixed solution was naturally cooled to room temperature and centrifuged. After washing and drying, a polymer-coated porous silicon composite material was obtained. The composite material was placed in a tube furnace and a layer of foamed titanium (m 混合物 :m 泡沫钛 =1:0.05), under the protection of argon atmosphere, the temperature was raised to 650°C at a heating rate of 5°C / min for high-temperature heat treatment for 4 hours, and then naturally cooled to room temperature; the obtained solid material was then washed three times by alternating centrifugation with deionized water and anhydrous ethanol, placed in a vacuum drying oven at a temperature of 100°C for 3 hours, and simply ground through a 325-mesh sieve to finally obtain a three-dimensional porous silicon composite material (comparative material 1).

[0109] Comparative Example 2

[0110] The preparation method of the silicon-carbon composite negative electrode material of this comparative example is as follows:

[0111] 1. Preparation of three-dimensional porous silicon

[0112] (1) Mechanically mix the strong reducing agent MgH2 and silicon dioxide powder in a mass ratio of 2:1 to obtain a mixture for standby use.

[0113] (2) Place the above mixture into a tube furnace and evenly spread a layer of titanium foam (m 混合物 :m 泡沫钛=1:0.05), under the protection of argon atmosphere, the temperature was raised to 650℃ at a heating rate of 5℃ / min for high-temperature heat treatment for 6h, and then naturally cooled to room temperature; the obtained solid material was placed in a prepared dilute hydrochloric acid (2mol / L) solution and soaked for 10min to remove metal oxides, and then washed three times by alternating centrifugation with deionized water and anhydrous ethanol, placed in a vacuum drying oven at a temperature of 100℃ for 3h, and after simple grinding and passing through a 325-mesh sieve, finally, a three-dimensional porous silicon negative electrode material was obtained.

[0114] 2. Preparation of polymer resin-coated porous silicon

[0115] 6 g of porous silicon powder, 5 g of melamine resin, and 2.5 g of urea were weighed and dissolved in 100 mL of deionized water. After ultrasonic dispersion, a mixed suspension was obtained. The suspension was transferred to a 200 mL hydrothermal reactor and kept at 150 ° C for 3 h to obtain a mixture solution. Then, the mixed solution was naturally cooled to room temperature and centrifuged. After washing and drying, a polymer-coated porous silicon composite material was obtained. The composite material was placed in a tube furnace and a layer of foamed titanium (m 混合物 :m 泡沫钛 =1:0.05), under the protection of argon atmosphere, the temperature was raised to 650°C at a heating rate of 5°C / min for high-temperature heat treatment for 4 hours, and then naturally cooled to room temperature; the obtained solid material was then washed three times by alternating centrifugation with deionized water and anhydrous ethanol, placed in a vacuum drying oven at a temperature of 100°C for 3 hours, and simply ground through a 325-mesh sieve to finally obtain a three-dimensional porous silicon composite material (comparative material 2).

[0116] Comparative Example 3

[0117] The preparation method of the silicon-carbon composite negative electrode material of this comparative example is as follows:

[0118] 1. Preparation of three-dimensional porous silicon

[0119] (1) Mechanically mix the strong reducing agent MgH2 and the silicon dioxide powder in a mass ratio of 6:1.5 to obtain a mixture for standby use.

[0120] (2) Place the above mixture into a tube furnace and evenly spread a layer of titanium foam (m 混合物 :m 泡沫钛=1:0.05), under the protection of argon atmosphere, the temperature was raised to 650℃ at a heating rate of 5℃ / min for high-temperature heat treatment for 6h, and then naturally cooled to room temperature; the obtained solid material was placed in a prepared dilute hydrochloric acid (2mol / L) solution and soaked for 10min to remove metal oxides, and then washed three times by alternating centrifugation with deionized water and anhydrous ethanol, placed in a vacuum drying oven at a temperature of 100℃ for 3h, and after simple grinding and passing through a 325-mesh sieve, finally, a three-dimensional porous silicon negative electrode material was obtained.

[0121] 2. Preparation of polymer resin-coated porous silicon

[0122] 2 g of porous silicon powder, 3 g of epoxy resin, and 1 g of melamine were weighed and dissolved in 100 mL of deionized water. After ultrasonic dispersion, a mixed suspension was obtained. The suspension was transferred to a 200 mL hydrothermal reactor and kept at 150 ° C for 3 h to obtain a mixture solution. The mixed solution was then naturally cooled to room temperature and centrifuged. After washing and drying, a polymer-coated porous silicon composite material was obtained. The composite material was placed in a tube furnace and a layer of foamed titanium (m 混合物 :m 泡沫钛 =1:0.05), under the protection of argon atmosphere, the temperature was raised to 650℃ at a heating rate of 5℃ / min for high-temperature heat treatment for 4h, and then naturally cooled to room temperature; the obtained solid material was placed in a prepared dilute hydrochloric acid (2mol / L) solution and soaked for 10min to remove the metaaluminate, and then washed three times by alternating centrifugation with deionized water and anhydrous ethanol, placed in a vacuum drying oven at a temperature of 100℃ for 3h, and after simple grinding and passing through a 325-mesh sieve, finally, a three-dimensional porous silicon composite material (comparative material 3) was obtained.

[0123] 3. Experimental Example: Application of Three-Dimensional Porous Silicon-Carbon Composite Materials in Lithium Batteries

[0124] Experimental Example 1

[0125] This experimental example tests the electrochemical properties of the silicon-carbon composite materials prepared in Examples 1 to 8 and Comparative Examples 1 to 3. The specific operation is as follows:

[0126] The silicon-carbon composite materials prepared in Examples 1-8 and Comparative Examples 1-3, the conductive agent SP, CMC, and SBR were mixed uniformly in deionized water at a mass ratio of 8:1:0.5:0.5 to form a slurry, and the mixture was evenly dispersed. Copper foil was pressed into discs with a diameter of 1.6 cm, then dried at 80°C under vacuum. The weight was measured and recorded as Weight 1. The mixed slurry was evenly applied to a copper foil current collector, dried at 80°C under vacuum for 12 hours, and then roll-pressed to form a negative electrode sheet. The weight was measured and recorded as Weight 2. The weight of the active material was obtained by subtracting Weight 1 from Weight 2, which was recorded as Weight 3. The dried sheet was transferred to a glove box, with a lithium sheet as the counter electrode. The electrolyte was 1M LiPF6 / EC:DEC (1:1; v / v), a mixture of ethylene carbonate and diethyl carbonate dissolved in lithium hexafluorophosphate. The separator was Celgard 2400. A button-type lithium-ion battery was assembled in a glove box with oxygen and water contents both less than 1 ppm. The assembled battery was left to stand for 12 hours, and the electrochemical performance of the static battery was tested on a blue battery tester with a constant current. The current was 1A / g×weight 3×0.8 (the first cycle current was 0.2A / g×weight 3×0.8), the voltage range was 0.01-1.5V, and the cycle was 100 times. The specific test results are shown in Table 1. The battery charge and discharge curve of the battery prepared by the silicon-carbon composite material of Example 4 after 100 cycles is shown in the figure below. Figure 3 shown.

[0127] Table 1 Electrochemical performance test results of silicon-carbon composite materials prepared in Examples 1-8 and Comparative Examples 1-3

[0128]

[0129] From Table 1 and Figure 3 It can be seen that the composite materials after high-temperature heat treatment of LiAlH4 and NaAlH4 have better discharge specific capacity after 100 cycles. Among them, the sample after high-temperature heat treatment of NaAlH4 has the best electrochemical performance. After 100 cycles, the discharge specific capacity is 1429.4% and the capacity retention rate is 87.9%.

[0130] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. The scope of patent protection of the present invention shall be based on the claims. Any equivalent structural changes made using the description and drawings of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A method for preparing a three-dimensional porous silicon-carbon composite material, characterized by: The following steps are involved: (1) Using silica as a silicon source, an organic polymer resin as a carbon source, and a nitrogen-containing organic matter as a nitrogen source, hydrothermal in-situ coating is performed, and after solid-liquid separation, a nitrogen-doped polymer resin-coated silica composite material is obtained; (2) The nitrogen-doped polymer resin-coated silica composite material obtained in step (1) is mixed with a metal hydride reducing agent, and then heated to 500-800° C. in an inert atmosphere for high-temperature heat treatment, and then washed and dried to obtain a silicon-carbon composite material.

2. The method for preparing a three-dimensional porous silicon-carbon composite material according to claim 1, wherein: The metal hydride reducing agent in step (2) is one of KH, NaH, CaH2, LiH, MgH2, LiAlH4, and NaAlH4; the mass ratio of the metal hydride reducing agent to the nitrogen-doped polymer resin-coated silica composite material is (2-6): (1-1.5).

3. The method for preparing a three-dimensional porous silicon-carbon composite material according to claim 1 or 2, characterized in that: The high temperature heat treatment time in step (2) is 4 to 8 hours.

4. The method for preparing a three-dimensional porous silicon-carbon composite material according to claim 1, wherein: The organic polymer resin in step (1) is one or more of resorcinol formaldehyde resin, melamine resin, urea formaldehyde resin, epoxy resin, acrylic resin, polyether polyester resin, furfural resin, and polyamide resin; and the nitrogen-containing organic matter is one or more of melamine polyphosphate, melamine, acrylonitrile, urea, and thiourea.

5. The method for preparing a three-dimensional porous silicon-carbon composite material according to claim 4, characterized in that: The mass ratio of silicon dioxide, organic polymer resin and nitrogen-containing organic matter in step (1) is (2-6): (3-5): (1-2.5).

6. The method for preparing a three-dimensional porous silicon-carbon composite material according to claim 1, characterized in that: The hydrothermal in-situ coating in step (1) is carried out at 60-240° C. for 2-4 hours.

7. The method for preparing a three-dimensional porous silicon-carbon composite material according to claim 1, characterized in that: The particle size of the silicon dioxide is 0.1 μm-30 μm.

8. The method for preparing a three-dimensional porous silicon-carbon composite material according to claim 1 or 2, characterized in that: The washing includes pickling to remove by-products of high temperature heat treatment.

9. A three-dimensional porous silicon-carbon composite material prepared by the method for preparing a three-dimensional porous silicon-carbon composite material according to any one of claims 1 to 8.

10. Use of the three-dimensional porous silicon-carbon composite material according to claim 9 in a lithium battery.

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