CN106848199B - Nano-silicon/porous carbon composite anode material of lithium ion battery and preparation method and application thereof - Google Patents

Abstract

The invention discloses a nano-silicon/porous carbon composite cathode material of a lithium ion battery and a preparation method and application thereof, wherein the composite cathode material is a core-shell structure material consisting of a porous nano-silicon particle core and a porous carbon layer shell; the preparation method is simple and low in cost, large-scale production is met, and the prepared composite negative electrode material can be used for preparing a lithium ion battery and shows high capacity and excellent cycle and rate performance.

Description

A kind of nano-silicon/porous carbon composite negative electrode material for lithium ion battery and preparation method thereof and application

technical field

The invention relates to a silicon-carbon composite material, in particular to a nano-silicon/porous carbon composite negative electrode material with a core-shell structure, and its application in preparing a lithium ion battery with high capacity and excellent rate performance; it belongs to battery material technology field.

Background technique

With the rapid population expansion and rapid economic development, electrochemical energy storage, mainly in the form of lithium-ion batteries, has received great attention due to its environmental friendliness, long cycle life, low self-discharge, high energy density and high voltage. It has been widely used in various portable electronic products. However, affected by the lithium storage mechanism and low capacity of existing graphite anode materials, it is difficult for commercial lithium-ion batteries to meet the needs of high energy density such as electric vehicles. Silicon is the anode material with the highest known theoretical capacity (4200mAh/g), which is much higher than the commercial graphite anode material (372mAh/g). It also has abundant crustal reserves and suitable working voltage. One of the capacity negative electrode materials.

However, as a semiconductor, silicon has poor conductivity to lithium ions and electrons, and the alloying reaction of silicon and lithium leads to the volume expansion of the particles during the charge and discharge process as high as ~300%, which can easily lead to damage to the electrode structure and severe battery capacity decay. The above problems severely limit the large-scale application of silicon anode materials. Reducing silicon particles to nanometer sizes, such as below 100 nm, and compounding them with conductive carbon materials has been proven to effectively improve their electrochemical performance, and is also the mainstream method currently adopted in the research of high-performance silicon anode materials.

At present, the preparation of nano-silicon particles is mainly by high-temperature magnesium thermal reduction of quartz (silicon dioxide) to prepare silicon blocks, and further synthesis of nano-silicon by laser ablation, vapor deposition or magnetron sputtering, etc. The synthesis method of this process route is cumbersome and costly. , and often have higher requirements for equipment. In the preparation of silicon/carbon composite materials, silicon nanoparticles and carbon precursors are often used directly for compounding. The carbon material completely coats the silicon particles during the compounding process. On the one hand, it can improve the conductivity of the silicon negative electrode, but at the same time, it also hinders to a certain extent. The speed of the electrochemical reaction between lithium ions and silicon materials.

The Chinese patent document with publication number CN105655555A discloses a method for preparing a silicon-carbon composite negative electrode material for lithium ion batteries. The silicon metal alloy material is mixed with graphite, and the porous silicon/carbon composite material is obtained through two pickling steps. The carbon composite material is mixed with an organic carbon source and heat-treated to obtain a silicon-carbon composite material, which improves the electrochemical performance of the silicon-based material to a certain extent. However, affected by the compact structure of the carbon material in the composite, the first discharge capacity and the first coulomb The efficiency is low, the rate performance is poor, and the overall electrochemical performance needs to be further improved.

SUMMARY OF THE INVENTION

Aiming at the problems of low first Coulomb efficiency and poor rate performance of existing silicon/carbon composite materials, the purpose of the present invention is to provide a special core-shell structure, which can effectively alleviate the volume change of silicon during charging and discharging, and improve the conductivity of silicon. Nano-silicon/porous carbon composite anode materials with good properties and electrochemical reactivity.

The second object of the present invention is to provide a method for preparing a nano-silicon/porous carbon composite negative electrode material for lithium ion batteries that is easy to operate, low in energy consumption and easy to mass-produce.

The third object of the present invention is to provide the application of the nano-silicon/porous carbon composite negative electrode material in lithium ion batteries, and preparing the negative electrode of lithium ion batteries can significantly improve the first Coulomb efficiency of lithium ion batteries, improve rate performance, etc. performance.

In order to achieve the above technical purpose, the present invention provides a nano-silicon/porous carbon composite negative electrode material for lithium ion batteries, which is a core-shell structure material composed of a porous nano-silicon particle inner core and a porous carbon layer outer shell.

The nano-silicon/porous carbon composite negative electrode material of the present invention has a special core-shell structure, the inner core is porous nano-silicon, the outer shell is a porous carbon layer, and the outer porous carbon layer not only provides a buffer for the volume expansion of the inner core nano-silicon during charging and discharging space, and improve the conductivity of nano-silicon. At the same time, the core nano-silicon has a porous structure, which has a large specific surface and high electrochemical activity, while the outer carbon layer is porous, which can provide lithium ion channels, which is conducive to improving the electrochemical reaction rate. Thereby improving the electrochemical performance of the negative electrode material.

In a preferred solution, the outer diameter of the core-shell structural material is 30-120 nm.

In a preferred solution, the thickness of the porous carbon layer shell is 1-10 nm.

In a preferred solution, the particle diameter of the inner core of the porous nano-silicon particle is 20-100 nm.

In a preferred solution, the silicon mass of the porous nano-silicon particles is 70-95% of the mass of the core-shell structure material. The ratio of silicon to carbon is controlled within an appropriate range, which can ensure that the porous carbon material evenly coats the nano-silicon particles, which can effectively improve the conductivity of the silicon particles and the reaction rate with lithium ions, which is helpful to further improve the prepared nano-silicon/porous Electrochemical properties of carbon composites, especially fast charge-discharge rate performance.

The present invention also provides a method for preparing the nano-silicon/porous carbon composite negative electrode material for lithium ion batteries. The method is to coat the surface of the aluminum-silicon alloy powder with an organic polymer layer, and then perform carbonization treatment to obtain a carbon layer coating. Aluminum-silicon alloy particles; the carbon-layer-coated aluminum-silicon alloy particles are obtained by acid etching to remove aluminum and create pores for the carbon layer.

In the technical scheme of the present invention, low-cost commercial aluminum-silicon alloy powder is used as the raw material, the surface of which is first coated with organic polymer, and then carbonized at high temperature. The key to the carbonized product lies in the use of acid treatment. The template effect makes the aluminum-silicon alloy form porous nano-silicon, and the volume is smaller than that of the aluminum-silicon alloy, leaving room for the expansion of the silicon volume; and the hydrogen generated during the violent reaction between acid and aluminum escapes, and the carbon layer is coated. Porous, that is, to obtain a nano-silicon/porous carbon composite negative electrode material with a special core-shell structure.

It can be seen from FIG. 1 that the technical route for preparing similar silicon-carbon materials in the past is different from the technical solution of the present invention, and the structural characteristics of the obtained silicon-carbon material are different. In the past, a method similar to acid etching for processing metal-silicon alloys is to use acid to etch the metal-silicon alloy first, and then to coat the carbon layer. The key to the technical solution of the present invention is to change the processing sequence of carbon coating and acid etching, first coating the carbon layer, then acid etching, and the acid etching process simultaneously realizes the removal of aluminum components in the aluminum silicon alloy and the carbon layer. porosity. Porous carbon layer not only improves the electrical conductivity of the composite material, but also facilitates the rapid diffusion of lithium ions, and can further buffer the volume expansion of silicon particles during charging and discharging.

In the technical scheme of the present invention, low-cost commercial aluminum-silicon alloy powder is used as the raw material, wherein the aluminum component can not only be used as a template for porous silicon, but also can react with an acid solution to generate hydrogen to escape, so that the coated carbon layer has a porous structure, There is no need to introduce additional templating agents (such as silica, etc.) for pore formation as in the previous method. Compared with the existing silicon/carbon composite material preparation method, the technical solution of the present invention can better solve the problems of the first Coulomb efficiency and rate of silicon, thereby further improving the electrochemical performance of the prepared composite material.

In a preferred solution, the process of coating the surface of the aluminum-silicon alloy powder with the organic polymer layer is as follows: mixing the alcohol dispersion of the aluminum-silicon alloy powder with the alcohol solution of the organic polymer, ultrasonically dispersing, and drying.

In a preferred solution, the mass of the organic polymer is 5-40% of the mass of the aluminum-silicon alloy powder. The thickness of the shell carbon layer of the nano-silicon/porous carbon composite anode material can be adjusted by adjusting the amount of organic polymer, which has a great influence on the electrochemical performance of the nano-silicon/porous carbon composite anode material.

In a preferred solution, the silicon content of the aluminum-silicon alloy powder is 5-40 wt %, and the particle size is 50-200 nm. In a further preferred solution, the silicon content in the aluminum-silicon alloy is 10-20 wt %, and the particle size of the aluminum-silicon alloy powder is 80-100 nm.

In a preferred solution, the organic polymer is polyvinylpyrrolidone. Preferably, polyvinylpyrrolidone can be carbonized to obtain a nitrogen-doped carbon material, which can further improve the conductivity of the carbon layer.

In a preferred solution, the molecular weight of the polyvinylpyrrolidone is 40,000 to 60,000.

In a preferred solution, the conditions for the carbonization treatment are: heat treatment at 400-800° C. for 4-8 hours under a protective atmosphere.

In a preferred solution, the acid etching process of the carbon layer-coated aluminum-silicon alloy particles is as follows: the carbon-layer-coated aluminum-silicon alloy particles are immersed in an acid solution with a H ⁺ concentration of 1-4 mol/L. The H ⁺ in the acid solution should not be lower than the stoichiometric molar amount for fully reacting aluminum in the aluminum-silicon alloy; the molar ratio of H ⁺ in the acid solution to aluminum in the aluminum-silicon alloy is 3:1 to 10:1; preferably 4:1～6:1. Preferably, the temperature of the etching process is 40-60°C. At this preferred temperature, the etching treatment time is 2 to 6 hours.

In order to further improve the performance of the silicon/carbon composite negative electrode material, the method of the present invention further includes a purification step for the nano-silicon/porous carbon composite negative electrode material; The hydrofluoric acid solution was impregnated, and then washed and dried to obtain a purified nano-silicon/porous carbon composite negative electrode material.

After the hydrofluoric acid treatment of the concentration, the residual products such as silicon oxide and other impurities after the etching treatment can be further removed, and the performance of the nano-silicon/porous carbon composite negative electrode material can be further improved. The treatment temperature in the purification process is preferably room temperature; at this preferred temperature, the treatment time is 8-14 h.

The aluminum-silicon alloy powder used in the technical solution of the present invention is prepared by the existing hot-melting mixing and spraying method, or using the existing commercial raw materials; its particle morphology is regular spherical, and more importantly, the aluminum and silicon in it are atomic The grades are uniformly mixed together and form Al-Si chemical bonds; the silicon particles obtained by the etching of the present invention are smaller in size and narrow in distribution. Compared with the existing general silicon and metal powder ball milling and re-etching method, the performance of the composite material prepared by the present invention is better.

The present invention also provides an application of the nano-silicon/porous carbon composite negative electrode material for lithium ion batteries, which is used as a negative electrode active material to prepare a negative electrode for lithium ion batteries.

In a preferred solution, the nano-silicon/porous carbon composite negative electrode material, the conductive carbon and the binder are prepared on the copper foil by a coating method to prepare a negative electrode material layer, that is, the negative electrode of the lithium ion battery is obtained.

The nano-silicon/porous carbon composite negative electrode material is used as the active material, and the negative electrode electrode of the lithium ion battery is prepared by using the existing lithium ion battery negative electrode electrode preparation technology together with a conductive agent and a binder. The conductive agent and binder used are existing conventional materials. Such as conductive carbon black, sodium carboxymethyl cellulose. For example, using sodium carboxymethyl cellulose as a binder to disperse in water, add the silicon/carbon composite material and carbon black to the prepared sodium carboxymethyl cellulose aqueous solution, and stir at room temperature for 8-12 hours to obtain a slurry; The slurry is coated on the copper foil and dried to obtain a negative electrode of silicon/carbon composite material; the content of silicon as an active component in the negative electrode is 50-80 wt%.

Relative to the prior art, the beneficial effects brought by the technical solution of the present invention are:

1. The nano-silicon/porous carbon composite negative electrode material of the present invention has a special structure, and is a core-shell structure material composed of a porous nano-silicon inner core and a porous carbon layer outer shell. The outer shell porous carbon layer not only provides buffer space for the volume expansion of the core nano-silicon during charge and discharge, but also improves the conductivity of the nano-silicon. At the same time, the outer shell carbon layer is porous, which can provide lithium ion channels, which is beneficial to improve the electrochemical reaction rate. . The core nano-silicon has a porous structure, its specific surface is large, and its electrochemical activity is high. Due to its special structure, the nano-silicon/porous carbon composite anode material exhibits excellent electrochemical performance and is used in lithium-ion batteries, with fast charge-discharge rate, high initial capacity, and excellent rate performance.

2. In the technical solution of the present invention, the preparation of the nano-silicon/porous carbon composite negative electrode material uses cheap aluminum-silicon alloy powder as the raw material, and the preparation method is simple, efficient, low energy consumption, and easy to mass-produce.

3. The nano-silicon/porous carbon composite negative electrode material of the present invention is used as a negative electrode active material to prepare a lithium ion battery, which exhibits excellent electrochemical performance, such as an initial reversible capacity of 2921mAh/g at a current density of 200mA/g, and a current of 500mA/g. The density initial capacity was 2105mAh/g, and the capacity remained 1826mAh/g after 100 cycles. The capacities are 2097, 2029 and 1980 mAh/g at high-rate current densities of 1000, 2000 and 3000 mA/g, respectively. With high capacity, excellent cycle and rate performance, it has great application prospects.

Description of drawings

[Fig. 1] is a schematic diagram of the difference between the technical method of the present invention and the previous method and the obtained material structure;

[Fig. 2] is a transmission electron microscope (TEM) image of the raw material aluminum-silicon alloy powder used in Examples 1-4;

[Fig. 3] is the thermogravimetric analysis (calculation of silicon content) of nano-silicon/porous carbon composites prepared in Examples 1-3;

[Fig. 4] is a transmission electron microscope (TEM) image of the nano-silicon/porous carbon composite prepared in Example 1;

[Fig. 5] is a transmission electron microscope (TEM) image of the nano-silicon/porous carbon composite prepared in Example 2;

[Fig. 6] is a transmission electron microscope (TEM) image of the nano-silicon/porous carbon composite prepared in Example 3;

[Fig. 7] is the cycle and rate performance diagram of the nano-silicon/porous carbon composite prepared in Example 1;

[Fig. 8] is the cycle and rate performance diagram of the nano-silicon/porous carbon composite prepared in Example 2;

[Fig. 9] is the cycle and rate performance diagram of the nano-silicon/porous carbon composite material prepared in Example 3;

[FIG. 10] is the cycle and rate performance diagram of the nano-silicon/carbon composite material prepared in Example 4.

Detailed ways

In order to make the technical means, creation features, achievement goals and effects of the present invention easy to understand and understand, the present invention will be further described below with reference to specific embodiments.

Example 1

Add 2 g of aluminum-silicon alloy powder (commercial aluminum-silicon alloy powder with a particle size of 50 to 200 nm) and 0.1 g of PVP into 30 mL and 20 mL of absolute ethanol, respectively, for ultrasonic dispersion for 5 minutes to obtain the suspension of aluminum-silicon alloy in absolute ethanol and For the solution of PVP in absolute ethanol, the two were mixed, sonicated for 5 min, and evaporated to dryness by magnetic stirring at 80° C. to obtain a solid powder. The powder was placed in a tube furnace in an argon atmosphere at 2°C/min and heated to 600°C for 4 hours to obtain carbon-coated aluminum-silicon alloy powder. 2 g of carbon-coated aluminum-silicon alloy powder was weighed and added to 80 mL of 4 mol/L hydrochloric acid aqueous solution, stirred at 40 °C for 4 h, filtered, washed, dried and ground to obtain solid powder. The powder was added to a 10 wt% hydrofluoric acid aqueous solution, reacted at room temperature for 12 h, and centrifuged with distilled water and anhydrous ethanol to obtain a nano-silicon/porous carbon composite negative electrode material, named as 92% Si/p-NC (silicon content of 92% is shown in Figure 3). Available).

Dissolve 15 mg of Na-CMC in 2 mL of deionized water and stir at room temperature for 4 h. Take 70 mg of nano-silicon/porous carbon and 15 mg of conductive carbon black powder, grind and mix evenly, add the Na-CMC solution to the solution and stir at room temperature for 12 h to obtain a negative electrode slurry, and use a coating machine to coat the prepared negative electrode slurry on copper foil at 110 °C After drying for 2 hours, the nano-silicon/porous carbon composite negative electrode was obtained by slicing, and the silicon content in the negative electrode was 64%. The obtained nano-silicon/porous carbon anode was paired with lithium metal, and a 1 mol/L LiPF ₆ EC/DEC (volume ratio 1:1) solution was used as the electrolyte to assemble a 2032 lithium-ion button battery for cycle performance testing.

Example 2

Add 2 g of aluminum-silicon alloy powder (commercial aluminum-silicon alloy powder with a particle size of 50 to 200 nm) and 0.3 g of PVP into 30 mL and 20 mL of absolute ethanol, respectively, for ultrasonic dispersion for 5 min to obtain the suspension of aluminum-silicon alloy in absolute ethanol and For the solution of PVP in absolute ethanol, the two were mixed, sonicated for 5 min, and evaporated to dryness by magnetic stirring at 80° C. to obtain a solid powder. The powder was placed in a tube furnace in an argon atmosphere at 2°C/min and heated to 600°C for 4 hours to obtain carbon-coated aluminum-silicon alloy powder. 2 g of carbon-coated aluminum-silicon alloy powder was weighed and added to 80 mL of 4 mol/L hydrochloric acid aqueous solution, stirred at 40 °C for 4 h, filtered, washed, dried and ground to obtain solid powder. The powder was added to a 10 wt% hydrofluoric acid aqueous solution, reacted at room temperature for 12 h, and centrifuged with distilled water and anhydrous ethanol to obtain a nano-silicon/porous carbon composite anode material, which was named 88% Si/p-NC (silicon content of 88% is shown in Figure 3). Available).

Dissolve 15 mg of Na-CMC in 2 mL of deionized water and stir at room temperature for 4 h. Take 70 mg of nano-silicon/porous carbon and 15 mg of conductive carbon black powder, grind and mix evenly, add the Na-CMC solution to the solution and stir at room temperature for 12 h to obtain a negative electrode slurry, and use a coating machine to coat the prepared negative electrode slurry on copper foil at 110 °C After drying for 2 hours, the nano-silicon/porous carbon composite negative electrode was obtained by slicing, and the silicon content in the negative electrode was 62%. The obtained nano-silicon/porous carbon anode was paired with lithium metal, and a 1 mol/L LiPF ₆ EC/DEC (volume ratio 1:1) solution was used as the electrolyte to assemble a 2032 lithium-ion button battery for cycle performance testing.

Example 3

Add 2 g of aluminum-silicon alloy powder (commercial aluminum-silicon alloy powder with a particle size of 50 to 200 nm) and 0.5 g of PVP into 30 mL and 20 mL of anhydrous ethanol, respectively, for ultrasonic dispersion for 5 min to obtain a suspension of aluminum-silicon alloy in anhydrous ethanol and For the solution of PVP in absolute ethanol, the two were mixed, sonicated for 5 min, and evaporated to dryness by magnetic stirring at 80° C. to obtain a solid powder. The powder was placed in a tube furnace in an argon atmosphere at 2°C/min and heated to 600°C for 4 hours to obtain carbon-coated aluminum-silicon alloy powder. 2 g of carbon-coated aluminum-silicon alloy powder was weighed and added to 80 mL of 4 mol/L hydrochloric acid aqueous solution, stirred at 40 °C for 4 h, filtered, washed, dried and ground to obtain solid powder. The powder was added to a 10 wt% hydrofluoric acid aqueous solution, reacted at room temperature for 12 h, and centrifuged with distilled water and anhydrous ethanol to obtain a nano-silicon/porous carbon composite negative electrode material, which was named as 79% Si/p-NC (the silicon content of 79% was shown in Figure 3). Available).

Dissolve 15 mg of Na-CMC in 2 mL of deionized water and stir at room temperature for 4 h. Take 70 mg of nano-silicon/porous carbon and 15 mg of conductive carbon black powder, grind and mix evenly, add the Na-CMC solution to the solution and stir at room temperature for 12 h to obtain a negative electrode slurry, and use a coating machine to coat the prepared negative electrode slurry on copper foil at 110 °C After drying for 2 hours, the nano-silicon/porous carbon composite negative electrode was obtained by slicing, and the silicon content in the negative electrode was 55%. The obtained nano-silicon/porous carbon anode was paired with lithium metal, and a 1 mol/L LiPF ₆ EC/DEC (volume ratio 1:1) solution was used as the electrolyte to assemble a 2032 lithium-ion button battery for cycle performance testing.

Example 4

This example is used as a comparison to illustrate the pore structure and electrochemical performance of the composite material not strictly following the technical route of the present invention or only using the previous method.

2g of aluminum-silicon alloy powder (commercial aluminum-silicon alloy powder with a particle size of 50-200nm) was added to 80mL of 4mol/L hydrochloric acid aqueous solution, stirred and reacted at 40°C for 4h, filtered, washed, dried and ground to obtain solid powder. The powder was added to a 10 wt% hydrofluoric acid aqueous solution, reacted at room temperature for 12 hours, and centrifuged with distilled water and absolute ethanol to obtain nano-silicon. Weigh 0.2g of nano-silicon powder and 0.3g of PVP and add them to 10mL and 20mL of anhydrous ethanol respectively for ultrasonic dispersion for 5min to obtain a suspension of nano-silicon in anhydrous ethanol and a solution of PVP in anhydrous ethanol, mix the two, Ultrasonic for 5 min, 80°C magnetic stirring to evaporate dry ethanol to obtain solid powder. The powder was placed in a tube furnace in an argon atmosphere at 2 °C/min and heated to 600 °C for 4 h to obtain a nano-silicon/carbon composite material, named Si/NC.

Dissolve 15 mg of Na-CMC in 2 mL of deionized water and stir at room temperature for 4 h. Take 70 mg of nano-silicon/carbon and 15 mg of conductive carbon black powder, grind and mix evenly, add the Na-CMC solution and stir at room temperature for 12 h to obtain a negative electrode slurry. The prepared negative electrode slurry is coated on the copper foil by a coating machine, and baked at 110 °C. After drying for 2 hours, the nano-silicon/carbon composite negative electrode was obtained by slicing, and the silicon content in the negative electrode was 62%. The obtained nano-silicon/carbon negative electrode was paired with lithium metal, and 1 mol/L LiPF ₆ EC/DEC (volume ratio 1:1) solution was used as the electrolyte to assemble a 2032 lithium ion button battery for cycle performance testing.

Table 1 shows the specific surface area and pore volume data of the composite materials prepared in Examples 1-4. It can be seen from the table that the specific surface area increases significantly after the carbon-coated aluminum-silicon alloy is etched by acid solution, and with the increase of carbon content, The specific surface area is getting larger and larger. Pore volume data demonstrate the existence of pores in the material after acid etching, with the 88%Si/p-NC sample having the largest pore volume. Among all the composite materials, the specific surface area and pore volume of the Si/NC sample obtained in Example 4 are significantly smaller than those of the Si/p-NC sample, indicating that the composite materials prepared without strictly following the technical route of the present invention or only using the previous method cannot obtain the present invention. Pore structure of the resulting material.

Figure 1 shows the technical method of the present invention and the structural schematic diagram of the prepared core-shell structure nano-silicon/porous carbon composite material. Using aluminum-silicon alloy powder as raw material, the prepared material can be significantly affected by changing the order of carbon coating and acid etching. Structure.

Transmission electron microscope Figure 2 shows that the Al-Si alloy raw material is spherical particles with a size of about 100 nm.

Figure 3 is the thermogravimetric curve of the nano-silicon/porous carbon composite material prepared in Examples 1-3. The content of the electrochemically active component silicon in the prepared composite material can be calculated from the thermogravimetric curve. As the amount of PVP increases, the coating The layer carbon content was gradually increased, and the silicon content decreased from 92% in Example 1 to 88% in Example 2 and 79% in Example 3, respectively.

It can be seen from Figure 4-6 of the transmission electron microscope that the particle size of the nano-silicon/porous carbon composite material prepared by the present invention is about 50-100 nm, and the porous carbon is evenly coated on the nano-silicon particles, and there is a small amount of agglomeration. 1-3 As the amount of PVP increases, the thickness of the carbon layer increases continuously.

Figures 7-9 are the electrochemical performance test results of Examples 1-3, respectively. It can be seen that the cycle performance and rate performance of Example 2 are better than those of Example 1 and Example 3, and the 88% Si/p-NC composite material is in The initial reversible capacity was 2921 mAh/g at 200 mA/g current density, 2105 mAh/g at 500 mA/g current density, and maintained at 1826 mAh/g after 100 cycles. The capacities are 2097, 2029 and 1980 mAh/g at high-rate current densities of 1000, 2000 and 3000 mA/g, respectively.

Fig. 10 is the electrochemical performance test result of the composite material obtained by the conventional method in Comparative Example 4 without strictly following the technical route of the present invention. It can be seen that the cycle and rate performance of the silicon/carbon composite material is significantly worse than that of the nano-silicon prepared by the present invention. /porous carbon composite, the initial capacity of 500mA/g current density is 1759mAh/g, and the capacity after 100 cycles is only 272mAh/g. The capacities are 1279, 1047 and 815 mAh/g at high rate current densities of 1000, 2000 and 3000 mA/g, respectively, which are about 50% of that of the nanosilicon/porous carbon composites.

Table 1: Data table of specific surface area and pore volume of composite materials prepared in Examples 1-4;

The main method features and advantages of the present invention for in-situ preparation of nano-silicon/porous carbon composite anode materials for lithium ion batteries are shown and described above. It should be understood by those skilled in the art that the present invention is not limited by the above-mentioned embodiments, and the descriptions in the above-mentioned embodiments and the description are only to illustrate the principles and methods of the present invention. There are also various changes and modifications which fall within the scope of the claimed invention. The claimed scope of the present invention is defined by the appended claims and their equivalents.

Claims (5)

1. A preparation method of a nano silicon/porous carbon composite cathode material of a lithium ion battery is characterized by comprising the following steps: coating an organic polymer layer on the surface of the aluminum-silicon alloy powder, and then carrying out heat treatment for 4-8 h at 400-800 ℃ under the condition of protective atmosphere to obtain carbon-coated aluminum-silicon alloy particles; removing aluminum from the carbon-coated aluminum-silicon alloy through acid etching, and forming a hole on a carbon layer to obtain the carbon-coated aluminum-silicon alloy;

the process of coating the organic polymer layer on the surface of the aluminum-silicon alloy powder comprises the following steps: mixing alcohol dispersion liquid of aluminum-silicon alloy powder with alcohol solution of organic polymer, performing ultrasonic dispersion, and drying; the mass of the organic polymer is 5-40% of that of the aluminum-silicon alloy powder; the organic polymer is polyvinylpyrrolidone, and the molecular weight of the polyvinylpyrrolidone is 4-6 ten thousand;

the nano silicon/porous carbon composite cathode material of the lithium ion battery is a core-shell structure material consisting of a porous nano silicon particle inner core and a porous carbon layer shell;

the outer diameter of the core-shell structure material is 30-120 nm; the thickness of the porous carbon layer shell is 1-10 nm; the particle size of the porous nano silicon particle inner core is 20-100 nm; the silicon mass of the porous nano silicon particles is 70-95% of the mass of the core-shell structure material.

2. The preparation method of the nano-silicon/porous carbon composite anode material for the lithium ion battery according to claim 1, characterized by comprising the following steps: the aluminum-silicon alloy powder has a silicon content of 5-40 wt% and a particle size of 50-200 nm.

3. The preparation method of the nano-silicon/porous carbon composite anode material for the lithium ion battery according to claim 1, characterized by comprising the following steps: the carbon layer coated aluminum-silicon alloy particles are subjected to acid etching by the following steps: coating aluminum-silicon alloy particles with carbon layer by adopting H⁺And (3) carrying out dipping treatment on the acid solution with the concentration of 1-4 mol/L at 20-60 ℃.

4. The application of the nano-silicon/porous carbon composite anode material of the lithium ion battery prepared by the preparation method of any one of claims 1 to 3 is characterized in that: the active material is used as a negative active material for preparing a negative electrode of a lithium ion battery.

5. The application of the nano-silicon/porous carbon composite anode material of the lithium ion battery as claimed in claim 4, is characterized in that: and preparing a negative material layer on the copper foil by using the nano silicon/porous carbon composite negative material, the conductive carbon and the binder through a coating method to obtain the lithium ion battery negative electrode.

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