CN118281184A

CN118281184A - Preparation method and application of silicon-carbon nanotube composite material

Info

Publication number: CN118281184A
Application number: CN202410190614.4A
Authority: CN
Inventors: 王结祥; 张帅; 张诺伟; 郑进保; 谢建榕
Original assignee: Gulei Petrochemical Research Institute Of Xiamen University
Current assignee: Gulei Petrochemical Research Institute Of Xiamen University
Priority date: 2024-02-21
Filing date: 2024-02-21
Publication date: 2024-07-02

Abstract

The invention discloses a preparation method of a silicon-carbon nanotube composite material, which comprises the following steps: (1) Preparing a uniform porous silicon material by taking metal silicon alloy powder as a raw material through etching; (2) Uniformly loading nano metal catalytic active components on the surface of the porous silicon substrate; (3) Adopting a vapor deposition method, and growing carbon nanotubes in situ under the action of a silicon-based surface catalyst to realize the coating of a carbon tube thin layer on silicon base; (4) The prepared silicon-carbon nanotube composite material can be applied to a negative electrode material of a lithium ion battery. The uniformly porous silicon substrate etched by the method is supported with the catalyst with controllable particle size and uniform dispersion, so that the in-situ grown carbon nano tube can effectively coat the silicon substrate to form a 3D conductive network, the in-situ grown rivet effect is more stable than the mechanical mixing of the surface of the silicon-carbon tube, and the in-situ grown rivet effect plays an effective buffering role in the silicon volume expansion process; the adjustment of the cladding thickness can be achieved by control of CVD process conditions.

Description

Preparation method and application of silicon-carbon nanotube composite material

Technical Field

The invention relates to the field of lithium ion batteries, in particular to a method for loading carbon nanotubes on micron silicon in situ and application of the method in a lithium ion battery cathode.

Background

With the rapid development of portable electronic equipment and electric automobiles, the demand of the automobile electronic industry for high-efficiency power supplies is rapidly increased, and lithium ion batteries become the most rapidly developed energy storage device at present due to the advantages of high energy density, high working voltage, long cycle life, no memory effect and the like. The negative electrode material is a key part in determining the energy density of the battery, and thus is receiving extensive attention and research. Currently, a cathode material capable of realizing large-scale application commercially is graphite, and the practical specific capacity of the cathode material is brought into play close to a theoretical value. Therefore, it is necessary to find a negative electrode material having a higher theoretical specific capacity, a long cycle life, high safety and stability, and low production cost

The silicon cathode material has the advantages of higher energy density, lower cost, environmental friendliness and the like, and the theoretical specific capacity of Si is 4200mAhg ^-1 which is about ten times of the theoretical capacity of graphite, so that the silicon cathode material is considered as a new generation of lithium ion battery cathode material with great development prospect. However, the silicon-based negative electrode can generate 400% volume expansion in the processes of lithium alloying and de-alloying, and repeated volume changes of the silicon-based negative electrode can lead to structural damage material pulverization of an electrode material and repeated formation of an SEI film in the working process of a battery, so that irreversible loss of active Li+ and rapid attenuation of capacity are caused, and the first coulombic efficiency and the cycle life of the silicon-based material are reduced. And secondly, the silicon-based material has poor conductivity and rate capability, and the silicon cathode is difficult to apply in a lithium battery due to various reasons.

The current modification methods for the silicon cathode are mainly two methods, namely firstly preparing the silicon cathode into special structures such as silicon nanowires, silicon nanotubes and silicon films, and secondly compounding silicon-based materials with good conductivity and strong mechanical properties such as metals, carbon materials and organic high-molecular polymers. The most common practice is to coat the nano silicon with carbon under the condition of Wen Tanyuan, and the carbon material coating can relieve the volume expansion of the silicon in charge and discharge and improve the conductivity of the silicon cathode. Common carbon-based materials include natural graphite negative electrode, artificial graphite negative electrode, intermediate phase carbon microsphere (MCMB), soft carbon (such as coke) negative electrode, hard carbon negative electrode, carbon nanotube, graphene, carbon fiber and the like, and the carbon nanotube has the advantages of high conductivity and high mechanical property, and the carbon nanotube and silicon nanoparticle are mixed in situ and granulated by a spray dryer to form the spherical structure of the carbon nanotube coated silicon nanoparticle. And compounding the carbon nano tube and the silicon nano particles through electrostatic self-assembly to form a coating structure. However, the method has the problem of uneven coating of the carbon nano tube, adopts the porous silicon supported metal catalyst to grow the carbon nano tube in situ, adopts the porous silicon etched by the silicon aluminum alloy, has simple preparation method and low cost, and is easy for large-scale production. And compared with a catalyst loading method by an impregnation method, the metal nano particles prepared by an oil phase method are controllable in particle size, nano metal particles are uniformly loaded inside and outside the silicon holes, and the carbon nano tubes are uniformly coated to form a 3D conductive network while relieving the charge-discharge volume expansion of the silicon negative electrode, so that the circulation stability and the conductivity of the silicon negative electrode are improved.

Disclosure of Invention

The invention aims to provide a method for in-situ loading of carbon nanotubes on micron silicon and application of the method in a lithium ion battery cathode, which solve the problem of volume expansion of silicon in the cyclic charge and discharge of a lithium ion battery, improve the conductivity of the silicon and improve the cyclic stability of the battery.

The aim of the invention can be achieved by the following technical scheme:

A preparation method of a silicon-carbon nanotube composite material comprises the following steps:

(1) Metal silicon alloy powder is used as a raw material, metal atoms are removed through etching, and porous silicon base with uniformly dispersed pore channels is prepared;

(2) Preparing uniformly dispersed nano metal particle solution by a thermal decomposition method, adding a certain amount of absolute ethyl alcohol into the nano metal particle solution, centrifuging to obtain nano metal particle solution, uniformly mixing nano metal particles and the porous silicon base obtained in the step (1) in toluene, centrifuging and vacuum drying to obtain metal-loaded porous silicon base, and marking as M/Si, wherein M represents corresponding metal elements;

(3) And (3) adopting a vapor deposition method, taking uniformly grinded M/Si as a catalyst, loading the catalyst into a tubular reactor, and introducing a carbon source containing water vapor and under a certain atmosphere for reaction to form the CNT/M/Si coated composite material.

Preferably, the metal silicon alloy powder in the step (1) is one of silicon aluminum alloy, silicon iron alloy, silicon copper alloy and silicon magnesium alloy.

The preparation method of the nano metal particle solution in the step (2) comprises the following steps: uniformly mixing metal salt, a surfactant and a solvent at room temperature, heating the mixture to 100 ℃ under an inert atmosphere, preserving the temperature of the mixed solution at 100 ℃ for 10-30min, quickly adding a reducing agent, heating to 180-230 ℃ at the speed of 10 ℃/min, preserving the temperature for 5-15min, and cooling to room temperature to obtain a nano metal particle solution.

Preferably, the metal salt is one of nickel acetylacetonate, iron acetylacetonate, cobalt acetylacetonate and copper acetylacetonate, the surfactant is one of oleylamine and oleic acid, the solvent is one of benzyl ether, octyl ether, phenyl ether and 1-octadecene, and the reducing agent is one of tributyl phosphorus, triphenylphosphine and tri-tert-butyl phosphorus.

Preferably, the carbon source in the step (3) is one of methane, ethylene and acetylene, the atmosphere is one of nitrogen, helium, hydrogen, argon and air, the particle size of the nano metal particles on the M/Si is between 5 and 25nm, and the vapor deposition reaction temperature is between 500 and 800 ℃.

The silicon-carbon nanotube composite material obtained by the preparation method is applied to the negative electrode of the lithium battery.

The invention has the following beneficial effects:

1. The silicon-aluminum alloy is obtained by etching in the acid solution, and has the characteristics of simplicity in operation, low cost and easiness in large-scale production.

2. Compared with the traditional metal salt precursor impregnation loading, the metal nano-particles prepared by the thermal decomposition method can control the particle size of the metal nano-particles by controlling the dosage of reactants, and the metal nano-particles and the carrier are loaded in the organic solvent, so that the uniform loading of the metal catalyst can be realized

3. According to the invention, in-situ growth of the coated silicon on the carbon nano tube can be realized by CVD in the tubular furnace by loading the catalyst on the surface of the porous silicon, compared with the traditional mechanical ball milling mixing mode and the like, the in-situ growth carbon nano tube has uniform coating degree on the silicon substrate and forms a 3D conductive network, and the carbon nano tube forms a 3D conductive network structure, so that the conductivity of the material can be effectively improved while a sufficient buffer space is provided for the volume expansion of the silicon material, and the cycle stability and the coulomb efficiency of the silicon composite material are improved.

Drawings

FIG. 1 is a metal nanoparticle transmission electron microscope image;

FIG. 2 is a statistical plot of particle size of metal nanoparticles;

FIG. 3 is a transmission electron microscope image of an M/Si composite;

FIG. 4 is a scanning electron microscope characterization of the CNT/M/Si composite;

FIG. 5 is a Raman characterization diagram of the CNT/M/Si composite;

FIG. 6 is a transmission electron microscope image of a bimetallic nanoparticle of an embodiment;

FIG. 7 is a graph showing particle size statistics of bimetallic nanoparticles of the example;

FIG. 8 is a perspective view of a trimetallic nanoparticle transmission electron microscope of an embodiment;

Fig. 9 is a statistical plot of particle size of trimetallic nanoparticles of the examples.

Detailed Description

In order to demonstrate the substantial features and significant advances of the present invention, further illustrative embodiments and effects thereof are described with the following examples.

Embodiment one:

1) Adding 2mol/l hydrochloric acid mixed solution into 1g of silicon-aluminum alloy powder, continuously stirring the mixed solution for 12 hours at 60 ℃, respectively washing and filtering the mixed solution with deionized water and absolute ethyl alcohol for three times until filtrate is neutral, and vacuum drying the obtained powder for 24 hours;

2) Mixing 500mg of nickel acetylacetonate with 30ml of benzyl ether and 5ml of oleylamine at room temperature under stirring, heating the mixed solution to 100 ℃ under the protection of nitrogen atmosphere, maintaining for 30min, rapidly adding 5ml of benzyl ether and 0.1ml of tributyl phosphorus, stirring for 20min at 100 ℃, then heating to 230 ℃ at a heating rate of 10 ℃/min, maintaining for 15min, and cooling to room temperature to obtain a nano metal particle solution. Wherein the transmission electron microscope characterization map (figure 1) and the particle size statistical distribution map (figure 2) of the nano metal particles.

3) Adding a certain amount of absolute ethyl alcohol into the nano metal particle solution, centrifuging for three times to obtain Ni metal nano particles, uniformly mixing the Ni metal nano particles with the porous silicon in the step 1) in toluene, centrifuging to obtain metal nano particles, uniformly mixing the metal nano particles with the porous silicon in toluene, centrifuging and vacuum drying to obtain metal-loaded porous silicon base, namely M/Si, and performing transmission electron microscope characterization on the M/Si (figure 3);

4) Uniformly grinding the M/Si composite material obtained in the step 3), placing the ground M/Si composite material into a tube furnace, heating to 600-800 ℃ at a heating rate of 6 ℃/min under the atmosphere of argon, introducing an acetylene carbon source, maintaining for 30-60min, and controlling the flow ratio of acetylene to argon to be 3:7, cooling to room temperature under argon atmosphere to obtain the CNT/M/Si composite material, and carrying out scanning electron microscope characterization (figure 4) and Raman spectrum characterization (5) on the CNT/M/Si composite material.

Embodiment two:

as in example 1, 1) was a silicon-magnesium alloy, 2) was 6ml of oleylamine and 0.2ml of tributylphosphorus, respectively. Example two nanoparticle transmission electron microscopy images (fig. 6) and particle size statistics images (fig. 7).

Embodiment III:

as for example 1, 1) was a ferrosilicon alloy, 2) was used, 8ml of oleylamine and 0.3ml of tributylphosphorus were used, respectively. Example three nanoparticle transmission electron microscopy (fig. 8), particle size statistics (fig. 9).

Comparative example 1:

1) Adding 1g of silicon-aluminum alloy powder into 2mol/l hydrochloric acid mixed solution, continuously stirring the mixed solution for 12 hours at 60 ℃, respectively washing and filtering the mixed solution with deionized water and absolute ethyl alcohol for three times until filtrate is neutral, and vacuum drying the obtained powder for 24 hours;

2) Uniformly mixing the powder in 1) with 0.249g of nickel nitrate and 60ml of deionized water, stirring at room temperature for 3 hours, centrifuging the mixed solution at 10000rpm for 10 minutes, and vacuum drying after three times of centrifugation to obtain the M/Si (impregnated) composite material

3) Grinding the M/Si (impregnated) composite material obtained in the step 2) uniformly, placing the ground M/Si (impregnated) composite material into a tube furnace, heating to 600-800 ℃ at a heating rate of 6 ℃/min under the atmosphere of argon, introducing an acetylene carbon source, maintaining for 30-60min, and controlling the flow ratio of acetylene to argon to be 3:7, then cooling to room temperature under argon atmosphere.

Comparative example 2:

1) Adding 81.6ml of deionized water into 1g of silicon-aluminum alloy powder, stirring and carrying out ultrasonic treatment for 30min, adding 19.7ml of concentrated hydrochloric acid into the mixed solution to prepare a hydrochloric acid mixed solution with the concentration of 2mol/l, continuously stirring the mixed solution for 12h at 60 ℃, respectively washing and filtering the mixed solution with deionized water and absolute ethyl alcohol for three times until filtrate is neutral, and carrying out vacuum drying on the obtained powder at 120 ℃ for 24h;

2) Porous silicon and commercial carbon nanotubes are mixed in the same ratio to obtain a CNT/Si (mechanical mixing) composite.

The composite finished products prepared in the above examples and comparative examples were subjected to material performance evaluation, the batteries were subjected to cyclic charge and discharge test using a blue electric tester with a measuring range of 5V/5mA, the specific discharge capacities of the batteries and after 200 cycles were tested at a current density of 1A/g, the capacity retention was calculated, and the test results were recorded in table 1:

TABLE 1 charge and discharge results

As shown by the test results in Table I, the invention of example 1, example 2 and example 3 not only has a certain specific discharge capacity, but also has capacity retention rates of 76.5%, 79.79% and 75.06% after 200 cycles, respectively, which indicates that nano nickel prepared by an oil phase method is uniformly loaded on porous silicon, and carbon nanotubes with different pipe diameters grown by CVD at a height of Wen Tanyuan can uniformly coat silicon, thereby relieving the volume expansion of silicon during the cyclic charge and discharge and improving the cycle stability of the battery. In contrast, in comparative example 1, the method of supporting the metal catalyst by the impregnation method, the uneven coating of the carbon tube grown by CVD with high Wen Tanyuan and low carbon yield result in the capacity retention rate of the battery after 200 cycles being only 54.8%, and in comparative example 2, the capacity retention rate after 200 cycles being only 13.7% although the initial discharge specific capacity is 3090.16mAhg ^-1 after the carbon nanotube and the porous silicon are mixed in situ indicates that the simple mechanical mixing cannot effectively coat the porous silicon to cause the porous silicon to severely break up during the cyclic charge-discharge volume expansion and the capacity to accelerate the decay.

The above examples of the invention are, of course, merely illustrative of the invention and are not intended to be limiting of the invention in any way. Other variations and modifications will occur to those skilled in the art upon the above-described examples. All embodiments cannot be exemplified in detail here. Obvious changes and modifications which are extended by the technical proposal of the invention are still within the protection scope of the invention.

Claims

1. The preparation method of the silicon-carbon nanotube composite material is characterized by comprising the following steps of:

2. The method of claim 1, wherein the metal silicon alloy powder in step (1) is one of a silicon aluminum alloy, a silicon iron alloy, a silicon copper alloy, and a silicon magnesium alloy.

3. The method according to claim 1, wherein the step of preparing the nano-metal particle solution in the step (2) comprises the steps of: uniformly mixing metal salt, a surfactant and a solvent at room temperature, heating the mixture to 100 ℃ under an inert atmosphere, preserving the temperature of the mixed solution at 100 ℃ for 10-30min, quickly adding a reducing agent, heating to 180-230 ℃ at the speed of 10 ℃/min, preserving the temperature for 5-15min, and cooling to room temperature to obtain a nano metal particle solution.

4. The method according to claim 3, wherein the metal salt is one or a combination of nickel acetylacetonate, iron acetylacetonate, cobalt acetylacetonate and copper acetylacetonate, the surfactant is one of oleylamine and oleic acid, the solvent is one of benzyl ether, octyl ether, phenyl ether and 1-octadecene, and the reducing agent is one of tributyl phosphorus, triphenylphosphine and tri-tert-butyl phosphorus.

5. The method according to claim 1, wherein the carbon source in the step (3) is one of methane, ethylene, propylene and acetylene, the atmosphere is one of nitrogen, helium, hydrogen, argon and air, the particle size of the nano metal particles on the M/Si is between 5 and 25nm, and the vapor deposition reaction temperature is between 500 and 800 ℃.

6. Use of the silicon-carbon nanotube composite material obtained by the preparation method according to any one of claims 1 to 5 in a negative electrode of a lithium battery.