CN114242962B - Lithium orthosilicate and carbon coated nano-silicon composite material and preparation method and application thereof - Google Patents
Lithium orthosilicate and carbon coated nano-silicon composite material and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a lithium orthosilicate and carbon coated nano-silicon composite material, and a preparation method and application thereof, wherein the method comprises the following steps: sintering nano silicon in air atmosphere to generate a silicon oxide coating layer on the surface of the nano silicon; dispersing nano silicon with a silicon oxide coating layer in an organic solvent, adding lithium hydroxide monohydrate, and stirring to obtain a first suspension; adding the carbon nano tube and polyvinylpyrrolidone into an organic solvent for ultrasonic dispersion to obtain a second suspension; mixing the first suspension and the second suspension, stirring, heating and drying to obtain a precursor of the lithium orthosilicate and carbon-coated nano-silicon composite material; and carrying out heat treatment on the precursor to obtain the lithium orthosilicate and carbon-coated nano-silicon composite material. The composite material prepared by the invention has higher specific capacity, rate capability and cycle stability. The preparation method has the advantages of low preparation cost and simple preparation method, and is easy for industrial production.
Description
Technical Field
The invention relates to the field of lithium ion batteries, in particular to a lithium orthosilicate and carbon-coated nano-silicon composite material, and a preparation method and application thereof.
Background
Silicon has the advantages of high theoretical capacity, moderate working voltage, high utilization rate, environmental friendliness and the like, and is considered as one of the best choices for replacing widely used graphite cathodes of lithium ion batteries. However, the silicon negative electrode material has the problems of large volume change, low conductivity and ionic conductivity, unstable solid electrolyte interface and the like, so that the silicon is crushed and the capacity is seriously attenuated, and the practical application of the silicon negative electrode material is hindered. Among the numerous solutions, carbon recombination is a promising and remarkable solution, and is receiving increasing attention.
In the silicon/carbon composite anode material, silicon is used as a high-capacity active material, and carbon enhances conductivity and simultaneously slows down expansion of silicon. In order to solve the problems of poor conductivity and volume expansion of the silicon material, the modification method mainly comprises silicon particle size nanocrystallization, carbon coating and the like. The nanometer silicon powder is dispersed in a three-dimensional conductive network formed by graphene, so that the tight contact between the nanometer silicon powder and the graphene can be maintained, the diffusion path of lithium ions is shortened, and the electron conduction of an electrode material is ensured not to be lost. The carbon coating limits the volume expansion of silicon in charge-discharge circulation to a certain extent, avoids side reactions of silicon and electrolyte, and improves the electronic conductivity of the material. The technical means can achieve the technical effects of improving the capacity and conductivity of the anode material and improving the structural stability and the cycle stability of the material, but has high preparation cost and complex preparation process, and is not suitable for mass production.
Therefore, how to prepare the silicon-based composite material with excellent electrochemical performance at low cost is an urgent problem to be solved in developing the silicon anode material.
Disclosure of Invention
In view of the shortcomings of the prior art, the invention aims to provide a lithium orthosilicate and carbon coated nano-silicon composite material, and a preparation method and application thereof, and aims to solve the problem of high preparation cost of the traditional silicon-based composite material.
The technical scheme of the invention is as follows:
the preparation method of the lithium orthosilicate and carbon coated nano silicon composite material comprises the following steps:
sintering nano silicon in the air atmosphere at 300-600 ℃ for 1-5 hours to generate a silicon oxide coating on the surface of the nano silicon;
dispersing nano silicon with a silicon oxide coating layer in an organic solvent, adding lithium hydroxide monohydrate, and stirring to obtain a first suspension;
adding the carbon nano tube and polyvinylpyrrolidone into an organic solvent for ultrasonic dispersion to obtain a second suspension;
mixing the first suspension and the second suspension, stirring, heating and drying to obtain a precursor of the lithium orthosilicate and carbon-coated nano-silicon composite material;
and carrying out heat treatment on the precursor of the lithium orthosilicate and carbon-coated nano-silicon composite material to obtain the lithium orthosilicate and carbon-coated nano-silicon composite material.
Further, the nano silicon is prepared by the following method: and ball milling the micron silicon in absolute ethyl alcohol, and drying to obtain powdery nano silicon.
Further, the organic solvent is one or more of methanol, ethanol, glycol and propanol.
Further, the addition amount of the lithium hydroxide monohydrate is 10.5% -17.5% of the mass of the nano silicon.
Further, the mass ratio of the carbon nano tube to the polyvinylpyrrolidone is 1:1, and the mass ratio of the carbon nano tube to the nano silicon is 1:2.
Further, the step of performing heat treatment on the precursor of the lithium orthosilicate and carbon-coated nano-silicon composite material to obtain the lithium orthosilicate and carbon-coated nano-silicon composite material specifically comprises the following steps:
and (3) putting the precursor of the lithium orthosilicate and carbon-coated nano-silicon composite material into a sintering furnace, and performing heat treatment for 1-5 hours at the temperature of 800-1000 ℃ in an inert gas atmosphere to obtain the lithium orthosilicate and carbon-coated nano-silicon composite material.
Further, the temperature is raised to 800-1000 ℃ at a heating rate of 3-10 ℃/min.
Further, the inert gas is selected from one or more of nitrogen, helium and argon.
A lithium orthosilicate and carbon coated nano-silicon composite, comprising: nano silicon, lithium orthosilicate coated on the surface of the nano silicon and a carbon material coated on the surface of the lithium orthosilicate;
and/or the lithium orthosilicate and carbon coated nano-silicon composite material is prepared by adopting the preparation method.
The invention discloses application of a lithium orthosilicate and carbon-coated nano-silicon composite material as a lithium ion battery anode material.
The beneficial effects are that: the method comprises the steps of carrying out surface treatment on nano silicon, sintering the nano silicon in an air atmosphere to generate an oxide coating layer of silicon, then reacting the oxide coating layer with lithium hydroxide to obtain nano silicon coated by lithium orthosilicate, and finally compounding the nano silicon coated by lithium orthosilicate with a carbon material to obtain the nano silicon composite material coated by lithium orthosilicate and carbon. The lithium orthosilicate and carbon coated nano-silicon composite material prepared by the simple method realizes that the lithium orthosilicate is uniformly coated on the surface of the nano-silicon, and the carbon material forms a three-dimensional conductive network, so that the volume expansion of the nano-silicon is effectively limited, the direct contact between electrolyte and nano-silicon particles is reduced, and meanwhile, the electronic conductivity of the composite material is remarkably improved. Therefore, the lithium orthosilicate and carbon coated nano silicon composite material has higher specific discharge capacity, excellent rate capability and long-cycle stability. Meanwhile, the lithium orthosilicate and carbon coated nano silicon composite material has low preparation cost and simple preparation method, and is easy for industrial production.
Drawings
FIG. 1 is an X-ray powder diffraction pattern of a lithium orthosilicate and carbon coated nano-silicon composite material obtained in example 1;
FIG. 2 is a Raman spectrum of the lithium orthosilicate and carbon coated nano-silicon composite obtained in example 1 and comparative example 3;
FIG. 3 is a scanning electron microscope image of the lithium orthosilicate and carbon coated nano-silicon composite obtained in example 1;
FIG. 4 is a transmission electron microscope image of the lithium orthosilicate and carbon coated nano-silicon composite obtained in example 1;
FIG. 5 is a graph showing the rate performance test of the lithium orthosilicate and carbon coated nano-silicon composite materials obtained in example 1, example 3, and example 4;
FIG. 6 is a graph showing the specific discharge capacity versus cycle number of the lithium orthosilicate and carbon coated nano-silicon composite materials obtained in example 1, example 2, and comparative example 1;
FIG. 7 is a graph showing the specific discharge capacity versus cycle number of the lithium orthosilicate and carbon coated nano-silicon composites obtained in example 1, example 3, and example 4;
fig. 8 is an ac impedance test chart of the lithium orthosilicate and carbon coated nano-silicon composite obtained in example 1, example 2, and comparative example 1.
Detailed Description
The invention provides a lithium orthosilicate and carbon coated nano-silicon composite material, a preparation method and application thereof, and the invention is further described in detail below in order to make the purposes, technical schemes and effects of the invention clearer and more definite. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
The embodiment of the invention provides a preparation method of a lithium orthosilicate and carbon-coated nano-silicon composite material, which comprises the following steps:
s1, sintering nano silicon in an air atmosphere at 300-600 ℃ for 1-5 hours to generate a silicon oxide coating on the surface of the nano silicon;
s2, dispersing nano silicon with a silicon oxide coating layer in an organic solvent, adding lithium hydroxide monohydrate, and stirring to obtain a first suspension;
s3, adding the carbon nano tube and polyvinylpyrrolidone into an organic solvent, and performing ultrasonic dispersion to obtain a second suspension;
s4, mixing the first suspension and the second suspension, and then stirring, heating and drying to obtain a precursor of the lithium orthosilicate and carbon-coated nano-silicon composite material;
s5, performing heat treatment on the precursor of the lithium orthosilicate and carbon-coated nano-silicon composite material to obtain the lithium orthosilicate and carbon-coated nano-silicon composite material.
In this embodiment, the nano silicon is subjected to surface treatment, and sintered in an air atmosphere to form a silicon oxide coating layer, then reacted with lithium hydroxide to obtain lithium orthosilicate coated nano silicon, and finally compounded with a carbon material to obtain the lithium orthosilicate and carbon coated nano silicon composite material. That is, the lithium orthosilicate and carbon coated nano-silicon composite includes: the nano silicon substrate, lithium orthosilicate coated on the surface of the nano silicon substrate and a carbon material coated on the surface of the lithium orthosilicate.
In the lithium orthosilicate and carbon coated nano-silicon composite material, the lithium orthosilicate is a fast ion conductor, and the lithium orthosilicate coating layer can improve the ion conductivity of the composite material, effectively relieve the volume expansion effect of nano-silicon particles in the charge and discharge process, and simultaneously avoid the generation of an excessively thick solid electrolyte interface film by direct contact of the nano-silicon particles with electrolyte. The three-dimensional conductive network carbon material with the coating structure can be formed on the surface of the lithium orthosilicate coating layer after heat treatment by taking the carbon nano tube and polyvinylpyrrolidone as carbon sources. Therefore, the prepared lithium orthosilicate and carbon coated nano silicon composite material has higher specific capacity, rate capability and cycle stability. Meanwhile, the lithium orthosilicate and carbon coated nano silicon composite material has low preparation cost and simple preparation method, and is easy for industrial production.
The lithium orthosilicate and the carbon-coated nano silicon composite material provided by the embodiment are used as a lithium ion battery anode material, the specific capacity of the lithium ion battery anode material is better than that of other carbon-coated nano silicon composite materials, the voltage range is 0.01-3V, and the average specific discharge capacities are 1200.7mAh/g, 1098.08mAh/g, 937.37mAh/g, 822.9mAh/g and 734.16mAh/g respectively under the current densities of 0.1A/g, 0.2A/g, 0.5A/g, 1A/g and 2A/g.
In the embodiment, the nano silicon is used as a raw material, so that the price is low; the thermal oxidation treatment process is simple in the air atmosphere, and the preparation cost is low; the lithium hydroxide is used as a lithium source for lithiation treatment, so that uniform dispersion in atomic level is easy to realize, and a uniform lithium orthosilicate lithium ion conductor coating can be prepared; carbon nano tubes and polyvinylpyrrolidone are used as carbon sources, and a three-dimensional conductive network with a coating structure can be formed after heat treatment.
In step S1, in one embodiment, the nano-silicon is prepared by the following method: and (3) ball-milling the micron silicon in absolute ethyl alcohol with high energy, and drying to obtain powdery nano silicon (particle size is 50-200 nanometers). The nano silicon is obtained by high-energy ball milling of the micron silicon, and the nano silicon is used as a raw material, so that the price is low.
In step S2, nano silicon having a silicon oxide coating layer is dispersed in an organic solvent, lithium hydroxide monohydrate is added, and the mixture is stirred uniformly (for 5 to 15 minutes, for example, 10 minutes) to obtain a first suspension. In this step, the lithium source is uniformly dispersed in the first suspension.
In one embodiment, the lithium hydroxide monohydrate is added in an amount of 10.5% to 17.5% by mass of the nano-silicon. When the content is lower than 10.5%, the electrochemical performance of the prepared lithium orthosilicate and carbon coated nano silicon composite material is not obviously improved due to the fact that the consumption of a lithium source is too small, and when the content is higher than 17.5%, the lithium orthosilicate coating layer on the silicon surface is too thick, the capacity is difficult to develop, and the commercialized application is not facilitated.
In one embodiment, the organic solvent is one or more of methanol, ethanol, ethylene glycol, propanol, etc., without limitation thereto.
In step S3, the carbon nanotubes and polyvinylpyrrolidone are added to an organic solvent, and subjected to ultrasonic dispersion (for 20-40 minutes, for example, 30 minutes) to obtain a second suspension. The polyvinylpyrrolidone can uniformly disperse the carbon nanotubes in an organic solvent, amorphous carbon can be generated after subsequent heat treatment, nano silicon particles are coated, and meanwhile, the carbon nanotubes are mutually adhered to form a conductive network with a coating structure.
In one embodiment, the mass ratio of the carbon nanotubes to the nano-silicon is 1:2. The carbon nanotubes have low capacity, so that the addition amount of the carbon nanotubes is too low, and the cycle stability is poor due to too low addition amount.
In one embodiment, the organic solvent is one or more of methanol, ethanol, ethylene glycol, propanol, etc., without limitation thereto.
In one embodiment, the mass ratio of carbon nanotubes to polyvinylpyrrolidone is 1:1.
In step S4, in one embodiment, the stirring time is 5-15 minutes, such as 10 minutes. In one embodiment, the temperature of the heat drying is 100-110 ℃, such as 105 ℃.
In step S5, heat treatment is performed on the precursor of the lithium orthosilicate and carbon coated nano silicon composite material, in the heat treatment process, lithium hydroxide reacts with silicon oxide on the surface of nano silicon to generate lithium orthosilicate, polyvinylpyrrolidone is subjected to carbonization reaction to generate amorphous carbon, nano silicon particles are coated, and carbon nanotubes are adhered to each other to form a conductive network with a coating structure, so that the lithium orthosilicate and carbon coated nano silicon composite material is obtained.
In one embodiment, the step of performing heat treatment on the precursor of the lithium orthosilicate and carbon coated nano-silicon composite material to obtain the lithium orthosilicate and carbon coated nano-silicon composite material specifically comprises the following steps:
and (3) putting the precursor of the lithium orthosilicate and carbon-coated nano-silicon composite material into a sintering furnace, and performing heat treatment for 1-5 hours at the temperature of 800-1000 ℃ in an inert gas atmosphere to obtain the lithium orthosilicate and carbon-coated nano-silicon composite material.
In one embodiment, the temperature is increased to 800-1000 ℃ at a rate of 3-10 ℃/min. For example, the heating rate may be 3 ℃/min, 5 ℃/min, 10 ℃/min, or the like. By controlling the temperature rising rate during heat treatment, the reaction process can be more stable, and the reaction can be more thoroughly carried out.
In one embodiment, after the heat treatment is finished, cooling, grinding and sieving are sequentially performed to obtain the lithium orthosilicate and carbon-coated nano-silicon composite material. Further, the cooling is performed at a certain cooling rate, and the cooling rate can be 5 ℃/min or 7 ℃/min, etc. The reaction process can be more stable and thorough by controlling the cooling rate. The heating rate and the cooling rate may be the same or different.
In one embodiment, the inert gas is selected from one or more of nitrogen, helium, argon, and the like.
The embodiment of the invention provides a lithium orthosilicate and carbon-coated nano-silicon composite material, which comprises the following components: nano silicon, lithium orthosilicate coated on the surface of the nano silicon and a carbon material coated on the surface of the lithium orthosilicate;
and/or the lithium orthosilicate and carbon coated nano-silicon composite material is prepared by adopting the preparation method disclosed by the embodiment of the invention.
According to the lithium orthosilicate and carbon coated nano-silicon composite material prepared by the simple method, the lithium orthosilicate is uniformly coated on the surface of the nano-silicon, a three-dimensional conductive network is formed by the carbon material, the volume expansion of the nano-silicon is effectively limited, the direct contact between electrolyte and nano-silicon particles is reduced, and meanwhile, the electronic conductivity of the composite material is remarkably improved. Therefore, the lithium orthosilicate and carbon coated nano silicon composite material has higher specific discharge capacity, excellent rate capability and long-cycle stability.
The embodiment of the invention provides an application of the lithium orthosilicate and carbon-coated nano-silicon composite material as a lithium ion battery anode material.
The lithium orthosilicate and carbon-coated nano-silicon composite material, the preparation method and the application thereof provided by the invention are further explained by specific preparation examples and comparative examples.
Example 1
Preparation of lithium orthosilicate and carbon coated nano-silicon composite precursor: sintering 1g of nano silicon powder for 3 hours at 450 ℃ in air atmosphere, cooling, ultrasonically dispersing into 50ml of ethanol solvent, adding 0.14g of lithium hydroxide monohydrate, and uniformly stirring to obtain a first suspension; dispersing 0.5g of carbon nano tube and 0.5g of polyvinylpyrrolidone in 100ml of ethanol solution, and performing ultrasonic dispersion to obtain uniformly dispersed second suspension; mixing the two suspensions, uniformly stirring, heating and drying to obtain the precursor of the lithium orthosilicate and carbon-coated nano-silicon composite material.
And (3) heat treatment: and (3) putting the obtained precursor of the lithium orthosilicate and carbon-coated nano-silicon composite material into a tube furnace, performing heat treatment for 3 hours at the temperature of 900 ℃ in an argon atmosphere, naturally cooling, grinding and sieving to obtain the powdery lithium orthosilicate and carbon-coated nano-silicon composite material.
Example 2
Preparation of silicon oxide and carbon coated nano silicon composite precursor: sintering 1g of nano silicon powder for 3 hours at the temperature of 450 ℃ in air atmosphere, cooling, ultrasonically dispersing into 50ml of ethanol solvent, and uniformly stirring to form a first suspension; dispersing 0.5g of carbon nano tube and 0.5g of polyvinylpyrrolidone in 100ml of ethanol solution, and performing ultrasonic dispersion to obtain uniformly dispersed second suspension; mixing the two suspensions, uniformly stirring, heating and drying to obtain the silicon oxide and carbon-coated nano silicon composite precursor.
And (3) heat treatment: and (3) putting the obtained silicon oxide and carbon-coated nano silicon composite precursor into a tube furnace, performing heat treatment for 3 hours at the temperature of 900 ℃ in an argon atmosphere, naturally cooling, grinding and sieving to obtain the powdery silicon oxide and carbon-coated nano silicon composite.
Example 3
Preparation of lithium orthosilicate and carbon coated nano-silicon composite precursor: sintering 1g of nano silicon powder for 3 hours at 450 ℃ in air atmosphere, cooling, ultrasonically dispersing into 50ml of ethanol solvent, adding 0.105g of lithium hydroxide monohydrate, and uniformly stirring to obtain a first suspension; dispersing 0.5g of carbon nano tube and 0.5g of polyvinylpyrrolidone in 100ml of ethanol solution, and performing ultrasonic dispersion to obtain uniformly dispersed second suspension; mixing the two suspensions, uniformly stirring, heating and drying to obtain the precursor of the lithium orthosilicate and carbon-coated nano-silicon composite material.
And (3) heat treatment: and (3) putting the obtained precursor of the lithium orthosilicate and carbon-coated nano-silicon composite material into a tube furnace, performing heat treatment for 3 hours at the temperature of 900 ℃ in an argon atmosphere, naturally cooling, grinding and sieving to obtain the powdery lithium orthosilicate and carbon-coated nano-silicon composite material.
Example 4
Preparation of lithium orthosilicate and carbon coated nano-silicon composite precursor: sintering 1g of nano silicon powder for 3 hours at the temperature of 450 ℃ in air atmosphere, cooling, ultrasonically dispersing into 50ml of ethanol solvent, adding 0.175g of lithium hydroxide monohydrate, and uniformly stirring to obtain a first suspension; dispersing 0.5g of carbon nano tube and 0.5g of polyvinylpyrrolidone in 100ml of ethanol solution, and performing ultrasonic dispersion to obtain uniformly dispersed second suspension; mixing the two suspensions, uniformly stirring, heating and drying to obtain the precursor of the lithium orthosilicate and carbon-coated nano-silicon composite material.
And (3) heat treatment: and (3) putting the obtained precursor of the lithium orthosilicate and carbon-coated nano-silicon composite material into a tube furnace, performing heat treatment for 3 hours at the temperature of 900 ℃ in an argon atmosphere, naturally cooling, grinding and sieving to obtain the powdery lithium orthosilicate and carbon-coated nano-silicon composite material.
Comparative example 1
Nano silicon powder is used.
Comparative example 2
Carbon nanotubes are used.
Comparative example 3
4.2g of lithium hydroxide monohydrate is weighed and dissolved in 200ml of water, the mixture is stirred uniformly, 1.5g of silicon dioxide is added after the mixture is fully dissolved, the mixture is fully stirred, the mixture is dried at 105 ℃, and the mixture is sintered for 3 hours at 900 ℃ in an air atmosphere, so that lithium orthosilicate is obtained.
In order to test that the composite material provided by the invention has the energy storage characteristic and can be used for a lithium ion battery cathode material, the materials obtained in the examples and the comparative examples are subjected to tests such as X-ray diffraction, raman spectrum, scanning electron microscope, transmission electron microscope, multiplying power performance of the composite material, cycle performance of the composite material, alternating current impedance spectrum of the composite material and the like, and the test results are shown in figures 1 to 8.
Specifically, fig. 1 is an X-ray diffraction chart of the composite material obtained in example 1, and it can be seen from the figure that the diffraction peak of the composite material is identical to the PDF card of pure silicon, and it is explained that the main component is silicon, and that the peak around 28 ° is a characteristic peak of carbon nanotubes. FIG. 2 is a Raman spectrum of the material obtained in example 1 and comparative example 3, wherein example 1 has a characteristic peak of silicon, a D peak, a G peak and a 2D peak which are characteristic of a carbon material, and the peak is 900cm -1 The presence of lithium orthosilicate in the composite material is evidenced by the presence of a peak of lithium orthosilicate. FIG. 3 is a lithium orthosilicate and carbon coated obtained in example 1The scanning electron microscope photograph of the nano silicon composite material shows that the carbon nano tube uniformly winds the nano silicon coated by the lithium orthosilicate, thereby forming a good three-dimensional conductive network. Fig. 4 is a transmission electron micrograph of the lithium orthosilicate and carbon coated nano-silicon composite material obtained in example 1, and the morphology feature of the composite material can be seen clearly as lattice fringes of silicon and a uniform lithium orthosilicate coating layer on the silicon surface. FIG. 5 is a graph showing the rate performance test of the materials obtained in examples 1, 3 and 4, wherein the average specific discharge capacities of the composite materials prepared by the invention are 1200.7mAh/g, 1098.08mAh/g, 937.37mAh/g, 822.9mAh/g and 734.16mAh/g under the current densities of 0.1A/g, 0.2A/g, 0.5A/g, 1A/g, 2A/g and 0.1A/g. FIG. 6 is a graph showing the cycle performance test of the materials obtained in comparative example 1, example 1 and example 2, wherein the composite material prepared in example 1 of the present invention has a specific discharge capacity of 1239.0mAh/g after 400 charge and discharge cycles at a current density of 0.5A/g, and the initial coulomb efficiency reaches 86.31%; the specific discharge capacities of the nano silicon powder of the comparative example 1 and the composite material prepared in the example 2 after 400 charge and discharge cycles are 527.5mAh/g and 773.2mAh/g respectively under the current density of 0.5A/g (the activation treatment is carried out at the current density of 0.1A/g in the first cycle). From this, it can be seen that the lithium orthosilicate and carbon coated nano-silicon composite material prepared in example 1 of the present invention is used as a negative electrode material of a lithium ion battery, and the specific capacity of the composite material is superior to that of the silicon oxide and carbon coated nano-silicon composite material prepared in example 2. FIG. 7 is a graph showing the cycle performance test of the composites prepared in example 1, example 2 and example 3 (the first cycle was conducted with an activation treatment at a current density of 0.1A/g), and the composites prepared in example 1 of the present invention exhibited the best specific capacity and stability. Fig. 8 is an ac impedance test chart of the composite materials prepared in comparative example 1 and example 2, and in example 1, compared with comparative example 1, the charge transfer resistance is reduced from 138.4Ω to 77.2Ω, and the method can significantly reduce the charge transfer resistance of the electrode and improve the electron conductivity of the composite material.
It is to be understood that the invention is not limited in its application to the examples described above, but is capable of modification and variation in light of the above teachings by those skilled in the art, and that all such modifications and variations are intended to be included within the scope of the appended claims.
Claims (9)
1. The preparation method of the lithium orthosilicate and carbon coated nano-silicon composite material is characterized by comprising the following steps:
sintering nano silicon in the air atmosphere at 300-600 ℃ for 1-5 hours to generate a silicon oxide coating on the surface of the nano silicon;
dispersing nano silicon with a silicon oxide coating layer in an organic solvent, adding lithium hydroxide monohydrate, and stirring to obtain a first suspension;
adding the carbon nano tube and polyvinylpyrrolidone into an organic solvent for ultrasonic dispersion to obtain a second suspension;
mixing the first suspension and the second suspension, stirring, heating and drying to obtain a precursor of the lithium orthosilicate and carbon-coated nano-silicon composite material;
performing heat treatment on the precursor of the lithium orthosilicate and carbon-coated nano-silicon composite material to obtain the lithium orthosilicate and carbon-coated nano-silicon composite material;
the addition amount of the lithium hydroxide monohydrate is 10.5-17.5% of the mass of the nano silicon.
2. The method for preparing the lithium orthosilicate and carbon coated nano-silicon composite material according to claim 1, wherein the nano-silicon is prepared by the following method: and ball milling the micron silicon in absolute ethyl alcohol, and drying to obtain powdery nano silicon.
3. The method for preparing a lithium orthosilicate and carbon coated nano-silicon composite material according to claim 1, wherein the organic solvent is one or more of methanol, ethanol, ethylene glycol, and propanol.
4. The method for preparing a lithium orthosilicate and carbon coated nano-silicon composite material according to claim 1, wherein the mass ratio of the carbon nanotubes to polyvinylpyrrolidone is 1:1, and the mass ratio of the carbon nanotubes to the nano-silicon is 1:2.
5. The method for preparing a lithium orthosilicate and carbon coated nano-silicon composite material according to claim 1, wherein the step of performing heat treatment on the precursor of the lithium orthosilicate and carbon coated nano-silicon composite material to obtain the lithium orthosilicate and carbon coated nano-silicon composite material specifically comprises:
and (3) putting the precursor of the lithium orthosilicate and carbon-coated nano-silicon composite material into a sintering furnace, and performing heat treatment for 1-5 hours at the temperature of 800-1000 ℃ in an inert atmosphere to obtain the lithium orthosilicate and carbon-coated nano-silicon composite material.
6. The method for preparing a lithium orthosilicate and carbon coated nano-silicon composite material according to claim 5, wherein the temperature is raised to 800-1000 ℃ at a temperature raising rate of 3-10 ℃/min.
7. The method of preparing a lithium orthosilicate and carbon coated nano-silicon composite according to claim 5, wherein the inert atmosphere is one or more selected from nitrogen, helium, and argon.
8. A lithium orthosilicate and carbon coated nano-silicon composite, comprising: nano silicon, lithium orthosilicate coated on the surface of the nano silicon, and a carbon material coated on the surface of the lithium orthosilicate,
the lithium orthosilicate and carbon coated nano-silicon composite material is prepared by the preparation method of any one of claims 1-6.
9. Use of the lithium orthosilicate and carbon coated nano-silicon composite material according to claim 8 as a negative electrode material of a lithium ion battery.
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