CN106848199B - Nano-silicon/porous carbon composite anode material of lithium ion battery and preparation method and application thereof - Google Patents
Nano-silicon/porous carbon composite anode material of lithium ion battery and preparation method and application thereof Download PDFInfo
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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
Technical Field
The invention relates to a silicon-carbon composite material, in particular to a nano silicon/porous carbon composite anode material with a core-shell structure and application thereof in preparing a lithium ion battery with high capacity and excellent rate performance; belongs to the technical field of battery materials.
Background
With the rapid expansion of population and the rapid development of economy, lithium ion batteries are the main form of electrochemical energy storage, and have attracted great attention due to their characteristics of environmental friendliness, long cycle life, small self-discharge, high energy density, high voltage and the like, and have been widely used in various portable electronic products. However, due to the influence of the lithium storage mechanism and low capacity of the existing graphite negative electrode material, the current commercial lithium ion battery is difficult to meet the use requirement of high energy density, such as electric vehicles and the like. Silicon is known as the anode material with the highest theoretical capacity (4200mAh/g), is much higher than the commercial graphite anode material (372mAh/g), has abundant crust storage and proper working voltage, and is considered as one of the most potential high-capacity anode materials.
However, silicon as a semiconductor has poor conductivity to lithium ions and electrons, and the volume expansion of particles is as high as-300% in the charging and discharging process due to the alloying reaction of silicon and lithium, which easily causes the structural damage of electrodes and the severe attenuation of battery capacity. The above problems severely limit the large-scale application of silicon anode materials. Reducing silicon particles to nanometer size, such as below 100nm, and compounding with conductive carbon materials has proven to be effective in improving their electrochemical performance, and is also the mainstream approach taken in the current research of high-performance silicon negative electrode materials.
At present, the preparation of nano silicon particles mainly comprises the steps of preparing a silicon block by high-temperature magnesium thermal reduction quartz (silicon dioxide), and further synthesizing nano silicon by methods such as laser ablation, vapor deposition or magnetron sputtering. In the aspect of preparation of the silicon/carbon composite material, silicon nanoparticles and a carbon precursor are often directly adopted for compounding, and the carbon material completely coats the silicon particles in the compounding process, so that on one hand, the conductivity of the silicon cathode can be improved, and on the other hand, the electrochemical reaction speed of lithium ions and the silicon material is also hindered to a certain extent.
Chinese patent publication No. CN105655555A discloses a method for preparing a silicon-carbon composite negative electrode material for a lithium ion battery, in which a silicon metal alloy material is mixed with graphite, and subjected to two acid pickups to prepare a porous silicon/carbon composite material, the porous silicon/carbon composite material is mixed with an organic carbon source, and subjected to a heat treatment to prepare a silicon-carbon composite material, which improves the electrochemical performance of the silicon-based material to a certain extent, but is affected by the compact structure of the carbon material in the composite, and the composite material has low first discharge capacity and first coulombic efficiency, poor rate capability, and needs to further improve the overall electrochemical performance.
Disclosure of Invention
Aiming at the problems of low coulombic efficiency, poor rate capability and the like of the existing silicon/carbon composite material for the first time, the invention aims to provide the nano silicon/porous carbon composite negative electrode material which has a special core-shell structure, can effectively relieve the volume change of silicon in the charge and discharge process and improve the conductivity and the electrochemical reaction activity of the silicon.
The second purpose of the invention is to provide a method for preparing the nano-silicon/porous carbon composite anode material of the lithium ion battery, which has the advantages of simple operation, low energy consumption and easy mass production.
The third purpose of the invention is to provide the application of the nano-silicon/porous carbon composite negative electrode material in the lithium ion battery, and the lithium ion battery negative electrode prepared from the nano-silicon/porous carbon composite negative electrode material can obviously improve the first coulombic efficiency of the lithium ion battery, and improve the rate capability and other performances.
In order to achieve the technical purpose, the invention provides a nano silicon/porous carbon composite anode material for a lithium ion battery, which is a core-shell structure material consisting of a porous nano silicon particle inner core and a porous carbon layer outer shell.
The nano silicon/porous carbon composite cathode material has a special core-shell structure, the inner core is porous nano silicon, the shell is a porous carbon layer, the porous carbon layer of the shell not only provides a buffer space for the volume expansion of the inner core nano silicon in the charging and discharging processes, but also improves the conductivity of the nano silicon, meanwhile, the inner core nano silicon has a porous structure, the specific surface is large, the electrochemical activity is high, and the carbon layer of the shell is porous, can provide a lithium ion channel, is favorable for improving the electrochemical reaction rate, and thus improves the electrochemical performance of the cathode material.
In a preferable scheme, the outer diameter of the core-shell structure material is 30-120 nm.
Preferably, the thickness of the porous carbon layer shell is 1-10 nm.
In a preferable scheme, the particle size of the porous nano silicon particle inner core is 20-100 nm.
In a preferred scheme, the silicon mass of the porous nano silicon particles is 70-95% of the mass of the core-shell structure material. The proportion of silicon and carbon is controlled in a proper range, so that the porous carbon material can be ensured to uniformly coat the nano silicon particles, the conductivity of the silicon particles and the reaction rate of the silicon particles and lithium ions can be effectively improved, and the electrochemical performance, especially the rapid charge-discharge rate performance, of the prepared nano silicon/porous carbon composite material can be further improved.
The invention also provides a preparation method of the nano silicon/porous carbon composite cathode material for the lithium ion battery, which comprises the steps of coating an organic polymer layer on the surface of aluminum-silicon alloy powder, and then carrying out carbonization treatment to obtain aluminum-silicon alloy particles coated by a carbon layer; and removing aluminum and forming pores on the carbon layer by acid etching of the aluminum-silicon alloy particles coated by the carbon layer.
According to the technical scheme, low-cost commercial aluminum-silicon alloy powder is used as a raw material, an organic polymer is coated on the surface of the raw material, then the raw material is carbonized at high temperature, the key point of a carbonized product is that acid treatment is adopted, aluminum can be etched and removed through acid, the aluminum-silicon alloy forms porous nano silicon by utilizing the template effect of the aluminum, the volume of the porous nano silicon is reduced relative to that of the aluminum-silicon alloy, and a space is reserved for silicon volume expansion; and hydrogen generated in the violent reaction process of acid and aluminum escapes, and the coated carbon layer is subjected to porosification, so that the nano silicon/porous carbon composite anode material with the special core-shell structure is obtained.
The difference between the prior preparation technical route of similar silicon-carbon materials and the technical scheme of the invention and the structural characteristics of the obtained silicon-carbon materials can be seen from figure 1. The prior method for processing the metal-silicon alloy by acid etching is to firstly corrode the metal-silicon alloy by acid and then coat a carbon layer. The key point of the technical scheme of the invention is that the carbon coating and acid etching treatment sequence is changed, the carbon layer is coated firstly, then the acid etching is carried out, and the acid etching process simultaneously realizes the removal of the aluminum component in the aluminum-silicon alloy and the porosification of the carbon layer. The carbon layer is subjected to porosification, so that the conductivity of the composite material is improved, the lithium ion is rapidly diffused, and the volume expansion of silicon particles in the charging and discharging process can be further buffered.
In the technical scheme of the invention, low-cost commercial aluminum-silicon alloy powder is used as a raw material, wherein an aluminum component can be used as a template of porous silicon and can react with an acid solution to generate hydrogen to escape so that the coated carbon layer has a porous structure, and the need of introducing an additional template agent (such as silicon dioxide and the like) for pore forming is avoided like the prior method. Compared with the existing preparation method of the silicon/carbon composite material, the technical scheme of the invention can better solve the problems of the first coulombic efficiency and the multiplying power of silicon, thereby further improving the electrochemical performance of the prepared composite material.
In a preferred embodiment, the process of coating the aluminum-silicon alloy powder with the organic polymer layer comprises: mixing the alcohol dispersion liquid of the aluminum-silicon alloy powder with the alcohol solution of the organic polymer, performing ultrasonic dispersion, and drying.
Preferably, the mass of the organic polymer is 5 to 40% of the mass of the aluminum-silicon alloy powder. The thickness of the carbon layer of the shell of the nano silicon/porous carbon composite anode material can be regulated and controlled by regulating and controlling the dosage of the organic polymer, and the electrochemical performance of the nano silicon/porous carbon composite anode material is greatly influenced.
Preferably, the aluminum-silicon alloy powder has a silicon content of 5 to 40 wt% and a particle size of 50 to 200 nm. In a further preferable scheme, 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 embodiment, the organic polymer is polyvinylpyrrolidone. Preferably, the polyvinylpyrrolidone is carbonized to obtain a nitrogen-doped carbon material, and the conductivity of the carbon layer can be further improved.
In a preferable scheme, the molecular weight of the polyvinylpyrrolidone is 4-6 ten thousand.
Preferably, the carbonization conditions are as follows: and (3) carrying out heat treatment for 4-8 h at 400-800 ℃ under the condition of protective atmosphere.
In a preferred embodiment, the process of acid etching the carbon-coated aluminum-silicon alloy particles comprises: coating aluminum-silicon alloy particles with carbon layer by adopting H+And (3) carrying out immersion treatment on the acid solution with the concentration of 1-4 mol/L. H in acid solution+Should not be less than the stoichiometric molar mass for fully reacting the aluminum in the aluminum-silicon alloy; h in acid solution+The molar ratio of the aluminum to aluminum in the aluminum-silicon alloy is 3: 1-10: 1; preferably 4:1 to 6: 1. Preferably, the temperature in the etching treatment process is 40-60 ℃. And under the preferable temperature, the etching treatment time is 2-6 h.
In order to further improve the performance of the silicon/carbon composite anode material, the method also comprises a purification step of the nano silicon/porous carbon composite anode material; and (3) dipping the prepared nano silicon/porous carbon composite negative electrode material by using a hydrofluoric acid solution with the mass concentration of 5-20%, and then washing and drying to obtain the purified nano silicon/porous carbon composite negative electrode material.
After the hydrofluoric acid treatment with the concentration, the impurities such as silicon oxide and the like remained after the etching treatment can be further removed, and the performance of the nano silicon/porous carbon composite negative electrode material is further improved. The treatment temperature in the purification process is preferably room temperature; the treatment time is 8-14 h at the optimal temperature.
The aluminum-silicon alloy powder adopted in the technical scheme of the invention is prepared by the existing hot-melting mixed spraying method, or the existing commercial raw materials are adopted; the particle morphology is regular spherical, more importantly, aluminum and silicon in the particles are uniformly mixed together at atomic level and form an Al-Si chemical bond; the silicon particles obtained by the etching of the invention have smaller particle size and narrow distribution. Compared with the existing general silicon and metal powder ball milling and etching method, the composite material prepared by the invention has better performance.
The invention also provides application of the nano silicon/porous carbon composite negative electrode material of the lithium ion battery, and the nano silicon/porous carbon composite negative electrode material is used as a negative electrode active material to be applied to preparation of a lithium ion battery negative electrode.
According to the preferable scheme, the negative electrode material layer is prepared on the copper foil by the coating method of the nano silicon/porous carbon composite negative electrode material, the conductive carbon and the binder, and then the negative electrode of the lithium ion battery is obtained.
The preparation method is characterized in that a nano silicon/porous carbon composite negative electrode material is used as an active substance, and the active substance, a conductive agent, a binder and the like are used for preparing the negative electrode of the lithium ion battery by adopting the conventional preparation technology of the negative electrode of the lithium ion battery. The adopted conductive agent and the adhesive are conventional materials. Such as conductive carbon black, sodium carboxymethyl cellulose. If sodium carboxymethylcellulose is used as a binder and dispersed in water, adding the silicon/carbon composite material and carbon black into a prepared sodium carboxymethylcellulose aqueous solution, and stirring at room temperature for 8-12 h to obtain slurry; coating the slurry on a copper foil, and drying to obtain a negative electrode of the silicon/carbon composite material; the content of active component silicon in the negative electrode is 50-80 wt%.
Compared with the prior art, the technical scheme of the invention has the beneficial effects that:
1. the nano silicon/porous carbon composite cathode material has a special structure and is a core-shell structure material consisting of a porous nano silicon inner core and a porous carbon layer shell. The shell porous carbon layer not only provides a buffer space for the volume expansion of the core nano silicon in the charging and discharging process, but also improves the conductivity of the nano silicon, and meanwhile, the shell porous carbon layer has the advantages of being porous, providing a lithium ion channel and being beneficial to improving the electrochemical reaction rate. And the inner core nano silicon has a porous structure, large specific surface and high electrochemical activity. Due to the special structure, the nano silicon/porous carbon composite negative electrode material shows excellent electrochemical performance, is used in a lithium ion battery, and has the advantages of high charge-discharge rate, high initial capacity and excellent rate performance.
2. According to the technical scheme, the nano silicon/porous carbon composite negative electrode material is prepared by taking cheap aluminum-silicon alloy powder as a raw material, and the preparation method is simple, efficient, low in energy consumption and easy for large-scale production.
3. The nano silicon/porous carbon composite negative electrode material is used as a negative electrode active material to prepare a lithium ion battery, and shows excellent electrochemical performance, such as initial reversible capacity of 2921mAh/g under a current density of 200mA/g, initial capacity of 2105mAh/g under a current density of 500mA/g, and capacity of 1826mAh/g is kept after 100 cycles. The capacities were 2097, 2029 and 1980mAh/g at 1000, 2000 and 3000mA/g, respectively, high current densities. High capacity, excellent cycle and rate performance and great application prospect.
Drawings
FIG. 1 shows the difference between the present invention and the prior art and the structure of the obtained material;
FIG. 2 is a Transmission Electron Microscope (TEM) image of the Al-Si alloy powder used as the raw material in examples 1 to 4;
FIG. 3 is a thermogravimetric analysis (calculation of silicon content) of the nano-silicon/porous carbon composite material 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 a graph showing the cycle and rate performance of the nano-silicon/porous carbon composite material prepared in example 1;
FIG. 8 is a graph showing the cycle and rate performance of the nano-silicon/porous carbon composite material prepared in example 2;
FIG. 9 is a graph showing the cycle and rate performance of the nano-silicon/porous carbon composite material prepared in example 3;
fig. 10 is a graph of cycle and rate performance of the nano silicon/carbon composite material prepared in example 4.
Detailed Description
In order to make the technical means, the creation characteristics, the achievement purposes and the effects of the invention easy to understand, the invention is further described with the specific embodiments.
Example 1
Adding 2g of aluminum-silicon alloy powder (commercial aluminum-silicon alloy powder with the particle size of 50-200 nm) and 0.1g of PVP into 30mL and 20mL of absolute ethyl alcohol respectively, carrying out ultrasonic dispersion for 5min to obtain a suspension of the aluminum-silicon alloy in the absolute ethyl alcohol and a solution of the PVP in the absolute ethyl alcohol, mixing the suspension and the solution, carrying out ultrasonic dispersion for 5min, and carrying out magnetic stirring at 80 ℃ to evaporate the absolute ethyl alcohol to obtain solid powder. And (3) placing the powder in a tube furnace in an argon atmosphere at the speed of 2 ℃/min, heating to 600 ℃ and treating for 4h to obtain the carbon-coated aluminum-silicon alloy powder. Weighing 2g of carbon-coated aluminum-silicon alloy powder, adding the powder into 80mL of 4mol/L hydrochloric acid aqueous solution, stirring and reacting for 4h at the temperature of 40 ℃, filtering, washing, drying and grinding to obtain solid powder. Adding the powder into 10 wt% hydrofluoric acid aqueous solution, reacting for 12h at room temperature, and centrifugally washing with distilled water and absolute ethyl alcohol to obtain the nano silicon/porous carbon composite negative electrode material which is named as 92% Si/p-NC (the silicon content is 92% and can be obtained from figure 3).
15mgNa-CMC was dissolved in 2mL deionized water and stirred at room temperature for 4 h. Grinding and uniformly mixing 70mg of nano-silicon/porous carbon and 15mg of conductive carbon black powder, adding the mixture into Na-CMC solution, stirring for 12 hours at room temperature to obtain negative electrode slurry, coating the prepared negative electrode slurry on copper foil by using a film coating machine, drying for 2 hours at 110 ℃, and slicing to obtain the nano-silicon/porous carbon composite negative electrode, wherein the silicon content in the negative electrode is 64%. Pairing the obtained nano silicon/porous carbon negative electrode with lithium metal, and mixing with 1mol/L LiPF6The EC/DEC (volume ratio 1:1) solution is used as electrolyte, and a 2032 lithium ion button cell is assembled for cycle performance test.
Example 2
Adding 2g of aluminum-silicon alloy powder (commercial aluminum-silicon alloy powder with the particle size of 50-200 nm) and 0.3g of PVP (polyvinyl pyrrolidone) into 30mL of absolute ethyl alcohol and 20mL of absolute ethyl alcohol respectively, carrying out ultrasonic dispersion for 5min to obtain a suspension of the aluminum-silicon alloy in the absolute ethyl alcohol and a solution of the PVP in the absolute ethyl alcohol, mixing the suspension and the solution, carrying out ultrasonic dispersion for 5min, and carrying out magnetic stirring at 80 ℃ to evaporate the absolute ethyl alcohol to obtain solid powder. And (3) placing the powder in a tube furnace in an argon atmosphere at the speed of 2 ℃/min, heating to 600 ℃ and treating for 4h to obtain the carbon-coated aluminum-silicon alloy powder. Weighing 2g of carbon-coated aluminum-silicon alloy powder, adding the powder into 80mL of 4mol/L hydrochloric acid aqueous solution, stirring and reacting for 4h at the temperature of 40 ℃, filtering, washing, drying and grinding to obtain solid powder. Adding the powder into 10 wt% hydrofluoric acid aqueous solution, reacting for 12h at room temperature, and centrifugally washing with distilled water and absolute ethyl alcohol to obtain the nano silicon/porous carbon composite negative electrode material which is named as 88% Si/p-NC (the silicon content of 88% can be obtained from figure 3).
15mgNa-CMC was dissolved in 2mL deionized water and stirred at room temperature for 4 h. Grinding and uniformly mixing 70mg of nano-silicon/porous carbon and 15mg of conductive carbon black powder, adding the mixture into Na-CMC solution, stirring for 12 hours at room temperature to obtain negative electrode slurry, coating the prepared negative electrode slurry on copper foil by using a film coating machine, drying for 2 hours at 110 ℃, and slicing to obtain the nano-silicon/porous carbon composite negative electrode, wherein the silicon content in the negative electrode is 62%. Pairing the obtained nano silicon/porous carbon negative electrode with lithium metal, and mixing with 1mol/L LiPF6The EC/DEC (volume ratio 1:1) solution is used as electrolyte, and a 2032 lithium ion button cell is assembled for cycle performance test.
Example 3
Adding 2g of aluminum-silicon alloy powder (commercial aluminum-silicon alloy powder with the particle size of 50-200 nm) and 0.5g of PVP (polyvinyl pyrrolidone) into 30mL of absolute ethyl alcohol and 20mL of absolute ethyl alcohol respectively, carrying out ultrasonic dispersion for 5min to obtain a suspension of the aluminum-silicon alloy in the absolute ethyl alcohol and a solution of the PVP in the absolute ethyl alcohol, mixing the suspension and the solution, carrying out ultrasonic dispersion for 5min, and carrying out magnetic stirring at 80 ℃ to evaporate the absolute ethyl alcohol to obtain solid powder. And (3) placing the powder in a tube furnace in an argon atmosphere at the speed of 2 ℃/min, heating to 600 ℃ and treating for 4h to obtain the carbon-coated aluminum-silicon alloy powder. Weighing 2g of carbon-coated aluminum-silicon alloy powder, adding the powder into 80mL of 4mol/L hydrochloric acid aqueous solution, stirring and reacting for 4h at the temperature of 40 ℃, filtering, washing, drying and grinding to obtain solid powder. Adding the powder into 10 wt% hydrofluoric acid aqueous solution, reacting for 12h at room temperature, and centrifugally washing with distilled water and absolute ethyl alcohol to obtain the nano silicon/porous carbon composite negative electrode material which is named as 79% Si/p-NC (the silicon content is 79% and can be obtained from figure 3).
15mgNa-CMC was dissolved in 2mL deionized water and stirred at room temperature for 4 h. Grinding and uniformly mixing 70mg of nano-silicon/porous carbon and 15mg of conductive carbon black powder, adding the mixture into Na-CMC solution, stirring for 12 hours at room temperature to obtain negative electrode slurry, coating the prepared negative electrode slurry on copper foil by using a film coating machine, drying for 2 hours at 110 ℃, and slicing to obtain the nano-silicon/porous carbon composite negative electrode, wherein the silicon content in the negative electrode is 55%. Pairing the obtained nano silicon/porous carbon negative electrode with lithium metal, and mixing with 1mol/L LiPF6The EC/DEC (volume ratio 1:1) solution is used as electrolyte, and a 2032 lithium ion button cell is assembled for cycle performance test.
Example 4
This example is a comparison to illustrate the pore structure and electrochemical performance of composites not strictly following the inventive technique or prepared by previous methods alone.
Adding 2g of aluminum-silicon alloy powder (commercial aluminum-silicon alloy powder with the particle size of 50-200 nm) into 80mL of 4mol/L hydrochloric acid aqueous solution, stirring and reacting for 4 hours at 40 ℃, filtering, washing, drying and grinding to obtain solid powder. Adding the powder into 10 wt% hydrofluoric acid water solution, reacting for 12h at room temperature, and centrifugally washing with distilled water and absolute ethyl alcohol to obtain the nano silicon. Weighing 0.2g of nano silicon powder and 0.3g of PVP, respectively adding the nano silicon powder and the PVP into 10mL of absolute ethyl alcohol and 20mL of absolute ethyl alcohol, carrying out ultrasonic dispersion for 5min to obtain a suspension of the nano silicon in the absolute ethyl alcohol and a solution of the PVP in the absolute ethyl alcohol, mixing the suspension of the nano silicon in the absolute ethyl alcohol and the solution of the PVP in the absolute ethyl alcohol, carrying out ultrasonic dispersion for 5min, and carrying out magnetic stirring at 80 ℃ to evaporate the absolute ethyl alcohol to. And (3) placing the powder in a tube furnace in an argon atmosphere at the temperature of 2 ℃/min, heating to 600 ℃ and treating for 4h to obtain the nano silicon/carbon composite material, which is named as Si/NC.
15mgNa-CMC was dissolved in 2mL deionized water and stirred at room temperature for 4 h. Grinding and uniformly mixing 70mg of nano silicon/carbon and 15mg of conductive carbon black powder, adding the mixture into Na-CMC solution, stirring the mixture for 12 hours at room temperature to obtain negative electrode slurry, coating the prepared negative electrode slurry on copper foil by using a film coating machine, drying the copper foil for 2 hours at 110 ℃, and slicing the copper foil to obtain nano silicon/carbon composite negative electrodeThe silicon content of the cathode was 62%. Pairing the obtained nano silicon/carbon negative electrode with lithium metal, and mixing with 1mol/L LiPF6The EC/DEC (volume ratio 1:1) solution is used as electrolyte, and a 2032 lithium ion button cell is assembled for cycle performance test.
Table 1 shows the specific surface area and pore volume data of the composite materials prepared in examples 1 to 4, and it can be seen from the table that the specific surface area is significantly increased after the carbon-coated aluminum-silicon alloy is etched by the acid solution, and the specific surface area is increased with the increase of the carbon content. The pore volume data demonstrated the presence of pores in the material after acid etching, with the 88% Si/p-NC sample having the largest pore volume. In all 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, which indicates that the composite material prepared not strictly according to the technical route of the invention or only by the conventional method cannot obtain the pore structure of the material obtained in the invention.
Fig. 1 shows a structural schematic of the core-shell structure nano silicon/porous carbon composite material prepared by the technical method of the invention, and the structure of the prepared material can be significantly influenced by changing the sequence of carbon coating and acid etching by using aluminum-silicon alloy powder as a raw material.
The transmission electron microscope figure 2 shows that the aluminum-silicon alloy raw material is spherical particles with the size of about 100 nm.
Fig. 3 is a thermogravimetric curve of the nano-silicon/porous carbon composite material prepared in examples 1-3, and the content of the electrochemically active component silicon in the prepared composite material can be calculated through the thermogravimetric curve, and the content of the carbon in the coating layer gradually increases with the increase of the PVP dosage, and the silicon content is respectively reduced from 92% in example 1 to 88% in example 2 and 79% in example 3.
As can be seen from the transmission electron microscope images in FIGS. 4-6, the particle size of the nano silicon/porous carbon composite material prepared by the invention is about 50-100 nm, the porous carbon uniformly coats the nano silicon particles, a small amount of agglomeration phenomenon exists, and the thickness of the carbon layer is continuously increased along with the increase of the consumption of PVP in examples 1-3.
FIGS. 7-9 are the results of electrochemical performance tests of examples 1-3, respectively, and it can be seen that the cycle performance and rate performance of example 2 are superior to those of examples 1 and 3, the initial reversible capacity of 88% Si/p-NC composite at 200mA/g current density is 2921mAh/g, the initial capacity of 500mA/g current density is 2105mAh/g, and the capacity remains 1826mAh/g after 100 cycles. The capacities were 2097, 2029 and 1980mAh/g at 1000, 2000 and 3000mA/g, respectively, high current densities.
Fig. 10 is a result of electrochemical performance test of the composite material obtained in comparative example 4 by the conventional method without strictly following the technical route of the present invention, and it can be seen that the cycling and rate performance of the silicon/carbon composite material is significantly inferior to that of the nano silicon/porous carbon composite material prepared by the present invention, the initial capacity of 500mA/g current density is 1759mAh/g, and the capacity after 100 cycles is only 272 mAh/g. The capacities at 1000, 2000 and 3000mA/g current densities were 1279, 1047 and 815mAh/g, respectively, which is about 50% of the nano-silicon/porous carbon composite material.
Table 1: tables of specific surface area and pore volume data of the composite materials prepared in examples 1 to 4;
the main method features and advantages of the invention for in-situ preparation of the nano-silicon/porous carbon composite anode material for lithium ion batteries are shown and described above. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are intended to illustrate the principles and procedures of the invention, but that various changes and modifications may be made without departing from the spirit and scope of the invention, and the invention is intended to be covered by the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.
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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| CN107623121B (en) * | 2017-10-18 | 2019-12-27 | 山东大学 | Metal-coated porous silicon composite electrode material and preparation method thereof |
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| CN110350181B (en) * | 2019-07-16 | 2021-08-24 | 昆明理工大学 | Preparation method of nano porous silicon negative electrode material of lithium ion battery |
| CN112670458B (en) * | 2019-10-16 | 2023-11-17 | 中国科学院福建物质结构研究所 | Preparation method and application of silicon-carbon material |
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| CN111769269B (en) * | 2020-07-10 | 2022-02-15 | 黄杰 | Porous polymer nano-silicon composite anode material and preparation method and application thereof |
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| CN115911292A (en) * | 2021-09-30 | 2023-04-04 | 贝特瑞新材料集团股份有限公司 | Negative electrode material, preparation method thereof and lithium ion battery |
| CN114551850A (en) * | 2022-01-25 | 2022-05-27 | 合肥国轩电池材料有限公司 | Silicon-carbon cathode composite material with porous structure and preparation method and application thereof |
| CN114639807A (en) * | 2022-03-04 | 2022-06-17 | 东华大学 | Porous silicon nanoparticle/porous carbon nanofiber composite electrode material and preparation method and application thereof |
| CN115020662A (en) * | 2022-06-01 | 2022-09-06 | 浙江工业大学 | Preparation method and application of core-shell structure porous silicon/carbon composite material |
| CN115275107B (en) * | 2022-09-28 | 2022-12-13 | 四川启睿克科技有限公司 | Silicon-based negative electrode with integrated structure and preparation method thereof |
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