CN109950475B - Flexible graphene-nano silicon composite membrane, preparation method and application thereof, and lithium ion battery - Google Patents
Flexible graphene-nano silicon composite membrane, preparation method and application thereof, and lithium ion battery Download PDFInfo
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Abstract
The invention provides a flexible graphene-nano silicon composite membrane, a preparation method and application thereof, and a lithium ion battery, and relates to the technical field of battery materials. The flexible graphene-nano silicon composite film provided by the invention not only can effectively improve the specific capacity, the cycle performance and the conductivity of lithium storage, but also has flexibility, can be bent and stretched, and has wide application prospects in the field of foldable energy storage products.
Description
Technical Field
The invention relates to the technical field of battery materials, in particular to a flexible graphene-nano silicon composite membrane, a preparation method and application thereof, and a lithium ion battery.
Background
With the rapid development of electronic technology, more and more electronic devices are developing in the direction of light weight, thinness and flexibility, some well-known enterprises have introduced flexible and foldable screens at home, and are planning to introduce products such as foldable mobile phones. At present, both a display assembly and a circuit can be flexible and foldable, but the biggest challenge is that foldable energy storage power supply products and traditional products such as lithium ion batteries and super capacitors are heavy in size and cannot be folded, and when the size is changed too much, short circuit can even occur between a positive electrode and a negative electrode, thermal runaway is caused, and serious safety problems are caused.
Therefore, in order to adapt to the development of the next-generation flexible electronic device, the development direction of the lithium ion battery should also develop towards flexibility and folding, and the obstacle to achieving the greatest flexibility is to use a flexible energy storage material, which is required to ensure that the flexible electrode has good mechanical properties and good electrochemical properties.
In view of the above, the present invention is particularly proposed.
Disclosure of Invention
One of the objectives of the present invention is to provide a flexible graphene-nano silicon composite film to improve the technical problem that the conventional energy storage power supply product cannot be folded.
The flexible graphene-nano silicon composite film provided by the invention comprises nano silicon and graphene, wherein the nano silicon is coated in a sheet layer of the graphene;
preferably, the graphene is multilayer graphene;
preferably, the particle size of the nano silicon is 10-200nm, preferably 10-80 nm.
The second purpose of the present invention is to provide a preparation method of the flexible graphene-nano silica composite film, which comprises the following steps:
(a) uniformly mixing nano silicon dioxide with positive charge groups loaded on the surface, graphene oxide and a metal sheet in a solvent, and carrying out redox reaction on the graphene oxide and the metal sheet to obtain a graphene oxide-nano silicon dioxide composite film loaded on the metal sheet;
(b) separating the metal sheet from the graphene oxide-nano silicon dioxide composite film to obtain a graphene oxide-nano silicon dioxide composite film;
(c) carrying out reduction treatment on the graphene oxide-nano silicon dioxide composite membrane to obtain a flexible graphene-nano silicon composite membrane;
preferably, in the step (a), the solvent is a mixed solution of a lower alcohol and water, preferably a mixed solution of ethanol and water;
further preferably, the volume ratio of ethanol to water is (1-2): (1-2), more preferably 1: 1.
Further, the nano-silica with the surface loaded with the positive groups is prepared by coupling treatment of the nano-silica with the coupling agent with the positive groups;
preferably, the positively charged group coupling agent is an aminosilane coupling agent;
preferably, the aminosilane coupling agent is selected from at least one of gamma-aminopropyltriethoxysilane, gamma-aminopropyltrimethoxysilane, N-beta (aminoethyl) -gamma-aminopropylmethyldimethoxysilane, N-beta (aminoethyl) -gamma-aminopropyltriethoxysilane, phenylaminomethyltriethoxysilane, phenylaminomethyltrimethoxysilane, aminoethylaminopropyltrimethoxysilane and polyaminoalkyltrialkoxysilane, preferably gamma-aminopropyltriethoxysilane.
Further, the mass ratio of the graphene oxide to the nano silicon dioxide is (70-95): (30-5), preferably (80-90): (10-20), preferably 85: 15.
Further, the metal sheet comprises at least one of an iron sheet, a magnesium sheet, a zinc sheet, an aluminum sheet and a copper sheet, and is preferably a zinc sheet.
Further, in the step (a), the time of the oxidation-reduction reaction is 8 to 16 hours, preferably 10 to 15 hours, and more preferably 12 hours.
Further, in the step (c), the graphene oxide-nano silicon dioxide composite membrane is subjected to high-temperature hydrogenation reduction treatment;
preferably, H is used2Carrying out high-temperature hydrogenation reduction treatment on the Ar mixed gas;
preferably, H2And Ar in a volume ratio of (5-20): (95-80), preferably (10-20): (90-80), more preferably 20: 80;
preferably, the temperature of the hydrogenation reduction is 700-900 ℃, and the time of the hydrogenation reduction is 10-15 h;
preferably, the temperature of the hydrogenation reduction is 750-850 ℃, and the time of the hydrogenation reduction is 11-13 h.
Preferably, the graphene oxide is formed by oxidation of graphite flakes;
and/or the nano silicon dioxide is prepared by a precipitation method.
The invention also aims to provide application of the flexible graphene-nano composite membrane provided by the invention or the flexible graphene-nano silicon composite membrane prepared by the preparation method of the flexible graphene-nano silicon composite membrane provided by the invention in a lithium ion battery cathode material.
The fourth purpose of the invention is to provide a lithium ion battery, which comprises the flexible graphene-nano composite film provided by the invention.
The flexible graphene-nano silicon composite film provided by the invention has the following beneficial effects:
(1) according to the flexible graphene-nano silicon composite membrane provided by the invention, the nano silicon is coated in the graphene sheet layer, so that the agglomeration of the nano silicon is reduced, and the graphene provides an effective buffer space for the volume expansion of the nano silicon, so that when the flexible graphene-nano silicon composite membrane is used as a lithium ion battery cathode material, the lithium storage specific capacity and the cycle performance can be effectively improved;
(2) the flexible graphene-nano silicon composite film provided by the invention effectively improves the conductivity through the mutual cooperation of the graphene and the nano silicon;
(3) the flexible graphene-nano silicon composite film provided by the invention not only has flexibility, but also can be bent and stretched, and has a wide application prospect in the field of foldable energy storage products.
The preparation method of the flexible graphene-nano silicon composite membrane provided by the invention is prepared by in-situ redox deposition and reduction sequentially through electrostatic coupling, is simple, has easily controlled process conditions, strong operability and good repeatability, can be suitable for large-scale production, is beneficial to improving the preparation efficiency and reducing the production cost.
Drawings
Fig. 1 is a TEM image of a flexible graphene-nano silicon composite film provided in example 1 of the present invention;
fig. 2 is an SEM image of the flexible graphene-nano silicon composite film provided in example 1 of the present invention;
fig. 3 is an XRD chart of the flexible graphene-nano silicon composite film provided in example 1 of the present invention;
fig. 4 is a test curve diagram of the flexible graphene-nano silicon composite film provided in embodiment 1 of the present invention in a new wilr BTS battery test system;
fig. 5 is a test curve diagram of the flexible graphene-nano silicon composite film provided in embodiment 2 of the present invention in a new wilr BTS battery test system.
Detailed Description
The technical solutions of the present invention will be described clearly and completely below, and it should be apparent that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The theoretical capacity of the graphite cathode material of the lithium ion battery is 370mAh/g, and the theoretical capacity is obviously bottleneck in the aspect of improving the energy density of the battery. Compared with a graphite cathode material, the silicon-based cathode material has obvious energy density advantage, the theoretical capacity is up to 4200mAh/g, and the capacity of an active substance in a battery can be improved, however, the volume expansion change of lithium intercalation/deintercalation of nano silicon is large and is about 300%, the conductivity is poor, the property is close to that of an insulator, more lithium ions are consumed, the irreversible capacity loss is caused, and the first charge-discharge efficiency is low. At present, a coating or highly dispersed system is formed mainly by adopting methods such as surface modification, doping, compounding and the like for modifying a high-capacity nano silicon negative electrode material, and the damage of internal stress generated by volume expansion in the lithium releasing and embedding process to a material structure is relieved by improving the mechanical property of the material, so that the electrochemical cycle stability of the material is improved.
In 2004, geom and Novoselov, two great scientists in uk, obtained single-layer multi-layer graphene for the first time through a mechanical stripping method, and then became popular research points all over the world, and the two scientists also obtained the nobel prize in 2010 due to the discovery. The multilayer graphene is formed by sp2The hybridized hexagonal honeycomb single-layer flaky crystal material formed by the carbon atoms has good heat conduction performance, mechanical characteristics and more lithium ion storage space, and the theoretical capacity of the material is 2 times that of graphite. In addition, the multilayer graphene belongs to a carbon nano material, the lithium ion diffusion path is short, the electron conduction rate is high, and the rate capability, the power performance and the safety performance of the material are improved.
In order to develop a high-performance flexible energy storage device, a person skilled in the art needs to develop a novel energy storage material.
According to a first aspect of the present invention, there is provided a flexible graphene-nano silicon composite film comprising nano silicon and graphene, wherein the nano silicon is coated in a sheet layer of the graphene.
In the present invention, "-" in the flexible graphene-nano silicon composite film represents "and".
The flexible graphene-nano silicon composite film provided by the invention has the following beneficial effects:
(1) according to the flexible graphene-nano silicon composite membrane provided by the invention, the nano silicon is coated in the graphene sheet layer, so that the agglomeration of the nano silicon is reduced, and the graphene provides an effective buffer space for the volume expansion of the nano silicon, so that when the flexible graphene-nano silicon composite membrane is used as a lithium ion battery cathode material, the lithium storage specific capacity and the cycle performance can be effectively improved;
(2) the flexible graphene-nano silicon composite film provided by the invention effectively improves the conductivity through the mutual cooperation of the graphene and the nano silicon;
(3) the flexible graphene-nano silicon composite film provided by the invention not only has flexibility, but also can be bent and stretched, and has a wide application prospect in the field of foldable energy storage products.
In a preferred embodiment of the present invention, the graphene is a multilayer graphene. By selecting the multilayer graphene to coat the nano silicon, the nano silicon can be more uniformly and completely coated. Typically, but not by way of limitation, the number of graphene layers is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15.
In a preferred embodiment of the present invention, the nano-silicon has a particle size of 10 to 200nm, preferably 10 to 80 nm.
By selecting the nano silicon with the particle size of 10-200nm to be coated in the graphene sheet layer, the specific surface area of the nano silicon is more favorably improved, so that the diffusion distance of lithium ions in the flexible graphene-nano silicon composite membrane is reduced, the lithium storage specific capacity of the flexible graphene-nano silicon is favorably improved, the permeation of electrolyte is facilitated, and the electronic conductivity of the flexible graphene-nano silicon composite membrane is improved. Particularly, when the particle size of the nano silicon is 10-80nm, the lithium storage specific capacity and the electronic conductivity of the flexible graphene-nano silicon composite film are higher. Typically, but not by way of limitation, the nanosilica has a particle size of, for example, 10, 20, 30, 40, 50, 60, 70, 80, 100, 120, 150, 180, or 200 nm.
According to a second aspect of the present invention, the present invention provides a preparation method of the above flexible graphene-nano silica composite film, comprising the steps of:
(a) uniformly mixing nano silicon dioxide with positive charge groups loaded on the surface, graphene oxide and a metal sheet in a solvent, and carrying out redox reaction on the graphene oxide and the metal sheet to obtain a graphene oxide-nano silicon dioxide composite film loaded on the metal sheet;
(b) separating the metal sheet from the graphene oxide-nano silicon dioxide composite film to obtain a graphene oxide-nano silicon dioxide composite film;
(c) and carrying out reduction treatment on the graphene oxide-nano silicon dioxide composite membrane to obtain the graphene-nano silicon composite membrane.
In the invention, in the step (a), the nano silicon dioxide with a surface loaded with positive charge groups and the graphene oxide with a surface loaded with a large number of negative charge groups (carboxyl and hydroxyl) are subjected to electrostatic adsorption, so that the nano disilicon is coated in a graphene oxide sheet layer; the graphene oxide and the metal sheet are subjected to oxidation-reduction reaction, and the graphene oxide is coated with nano silicon dioxide and deposited on the surface of the metal sheet under the action of oxidation and reduction motive power to form a graphene oxide-nano silicon dioxide composite film (deposited film); and (c) separating and reducing the deposited film and the metal sheet to obtain the flexible graphene-nano silicon composite film.
The preparation method of the flexible graphene-nano silicon composite membrane provided by the invention is prepared by in-situ redox deposition and reduction sequentially through electrostatic coupling, is simple, has easily controlled process conditions, strong operability and good repeatability, can be suitable for large-scale production, is beneficial to improving the preparation efficiency and reducing the production cost.
In a preferred embodiment of the present invention, the solvent used for dispersing the graphene oxide and the nanosilica loaded with positive charge groups in step (a) is a mixed solution of a lower alcohol and water. The lower alcohol is C1-C4 alcohol, such as methanol, ethanol, propanol and isopropanol.
In a further preferred embodiment of the present invention, the solvent is a mixed solution of ethanol and water, and the mixed solution of ethanol and water is used as the solvent, which is beneficial to uniformly mixing the graphene oxide and the nanosilicon dioxide loaded with positive charge groups.
When the volume ratio of the ethanol to the water is (1-2): (1-2), the graphene oxide and the nano-silica loaded with the positive charge groups are more favorably and uniformly mixed, and particularly, when the volume ratio of the ethanol to the water is 1:1, the graphene oxide is better in solubility, so that the graphene oxide and the nano-silica loaded with the positive charge groups are more uniformly mixed. Typically, but not limitatively, the volume of ethanol and water in the solvent is, for example, 1:2, 2:1 or 1: 1.
In a preferred embodiment of the present invention, the nanosilica with positively charged groups loaded on the surface is prepared by coupling the nanosilica with a coupling agent with positively charged groups. The nano silicon dioxide is coupled by adopting a coupling agent with a positive electric group, so that the coupling agent is coupled on the surface of the nano silicon dioxide, and the nano silicon dioxide loaded with the positive electric group is prepared.
In a preferred embodiment of the present invention, the positively charged group coupling agent is an aminosilane. The nano silicon dioxide is coupled by adopting the amino silane coupling agent, so that the amino silane coupling agent and the nano silicon dioxide are coupled more firmly. Typically, but not by way of limitation, the aminosilane coupling agent is selected from one or more of gamma-aminopropyltriethoxysilane, gamma-aminopropyltrimethoxysilane, N-beta (aminoethyl) -gamma-aminopropylmethyldimethoxysilane, N-beta (aminoethyl) -gamma-aminopropyltriethoxysilane, phenylaminomethyltriethoxysilane, phenylaminomethyltrimethoxysilane, aminoethylaminopropyltrimethoxysilane, and polyaminoalkyltrialkoxysilanes, and particularly when the aminosilane agent is gamma-aminopropyltriethoxysilane, the nanosilica is more strongly coupled to the coupling agent and the supported positively charged groups are more abundant.
In a preferred embodiment of the present invention, the mass ratio of graphene oxide to nano-silica is (70-95): (30-5), preferably (80-90): (10-20), preferably 85: 15.
By controlling the mass ratio of the graphene oxide to the nano silicon dioxide, the generated flexible graphene-nano silicon composite membrane is controlled to have flexibility, can be bent and extended, and also has good conductivity and lithium storage specific capacity. When the mass ratio of the graphite oxide silicon to the nano silicon dioxide is (80-90): (10-20), the flexibility, the conductivity and the lithium storage specific capacity of the prepared flexible graphene-nano silicon composite film; particularly, when the mass ratio of the graphene oxide to the nano silicon dioxide is 85:15, the prepared flexible graphene-nano silicon composite membrane has more excellent comprehensive performance.
Typically, but not limitatively, the nano-silica dispersion liquid with the surface loaded with positive charge groups is prepared according to the following steps:
dispersing part of nano silicon dioxide into dimethylbenzene, performing ultrasonic treatment, adding 3-aminopropyltriethoxysilane (KH550), heating to 80 ℃, refluxing under the protection of inert gas, performing suction filtration, washing with absolute ethyl alcohol for multiple times, and dispersing in absolute ethyl alcohol again to obtain nano silicon dioxide suspension with amino groups coupled on the surface.
In a preferred embodiment of the present invention, the metal sheet includes at least one of an iron sheet, a magnesium sheet, a chip, an aluminum sheet, and a copper sheet, and is preferably a zinc sheet. The metal sheet is selected according to the principle that the metal sheet can perform oxidation-reduction reaction with graphene oxide, so that the graphene oxide and the metal sheet can perform in-situ oxidation-reduction reaction.
In a preferred embodiment of the present invention, in step (a), the redox reaction time is from 8 to 16h, preferably from 10 to 15h, preferably 12 h. The time of the oxidation-reduction reaction is controlled to be 8-16h, so that the oxidation-reduction reaction is carried out more completely. Typically, but not by way of limitation, the redox reaction time is, for example, 8, 9, 10, 11, 12, 13, 14, 15, or 16 h.
In a preferred embodiment of the present invention, in the step (c), the graphene oxide-nano silica composite film is subjected to a high-temperature hydrogenation reduction treatment. By adopting high-temperature hydrogenation reduction treatment, the graphene oxide-nano silicon dioxide composite membrane is reduced more completely.
In a preferred embodiment of the invention, H is used2-Ar(H2And Ar) mixed gas is subjected to high-temperature hydrogenation reduction treatment to ensure that no other side reaction occurs in the reduction process, so that the purity of the generated flexible graphene-nano silicon composite membrane is ensured.
In a further preferred embodiment of the invention, H2And Ar in a volume ratio of (5-20): (95-80), preferably (10-20): (90-80), more preferably 20: 80. By controlling H2And Ar in a volume ratio of (5-20): (95-80) to improve the reduction efficiency while ensuring the completion of the reduction reaction; when H is present2And Ar in a volume ratio of (10-20): (90-80), the hydrogenation reduction efficiency is higher; especially when H is2And Ar in a volume ratio of 20:80, the hydrogenation reduction efficiency is higher.
Typically, but not by way of limitation, H2In the mixed gas of-Ar, H2And Ar is in a volume of, for example, 10:90, 12:88, 15:85, 18:82, 20:80, 22:78, 25:75, 28:78, or 30: 70.
In a preferred embodiment of the invention, the temperature of the hydrogenation reduction is 700-900 ℃, and the time of the hydrogenation reduction is 10-15 h. By controlling the temperature and time of hydrogenation reduction, the hydrogenation reduction reaction is carried out more completely, the performance of the flexible graphene-nano silicon composite membrane is better ensured, particularly the temperature of the hydrogenation reduction reaction is 750-850 ℃, and the time of the hydrogenation reduction is 11-13h, so that the efficiency of the hydrogenation reduction reaction is higher.
Typically, but not by way of limitation, the temperature of the hydrogenation reduction reaction is, for example, 700, 710, 730, 740, 750, 760, 770, 780, 790, 800, 810, 820, 830, 840, 850, 860, 870, 880, 890, or 900 ℃; the hydrogenation reduction time is, for example, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5 or 15 h.
In a preferred embodiment of the present invention, the graphene oxide is formed by oxidation of a graphite sheet. The graphene oxide is prepared by oxidizing the graphite flakes, so that the raw materials are cheaper, and the cost is lower.
Typically, but not by way of limitation, graphene oxide is prepared as follows:
(1) dispersing graphite flakes in concentrated sulfuric acid, stirring uniformly, slowly adding potassium permanganate powder, stirring for 30min, and reacting at 45 ℃ for 24h to obtain a reaction solution.
(2) And (2) cooling the reaction liquid obtained in the step (1) to room temperature, pouring the reaction liquid into ice water, adding hydrogen peroxide at room temperature until the mixed liquid turns brown yellow, then performing centrifugal separation, washing with dilute hydrochloric acid, washing with deionized water until the pH value is 6.8-7.2, and dialyzing for one week by using a dialysis bag to obtain the graphene oxide dispersion liquid.
In a preferred embodiment of the invention, the nanosilica is prepared by precipitation. The nano silicon dioxide prepared by the precipitation method is cheaper in raw material and easier in process condition control, so that the preparation cost can be effectively reduced.
Typically, but not by way of limitation, nanosilica is prepared as follows:
weighing a mixed solution of distilled water, hydrochloric acid and absolute ethyl alcohol according to a certain proportion, slowly dropwise adding ethyl orthosilicate under the stirring condition, stirring, filtering, washing with absolute ethyl alcohol and drying to obtain the nano silicon dioxide.
According to a third aspect of the invention, the invention provides an application of a flexible graphene-nano silicon composite membrane in a lithium ion battery anode material.
When the flexible graphene-nano silicon composite film provided by the invention is used as a lithium ion battery cathode material, the lithium storage specific capacity and the cycle performance can be effectively improved, the conductivity can be improved, and the flexible graphene-nano silicon composite film has flexibility, can be bent and extended, and has a wide application prospect in a foldable lithium ion battery.
The technical solution provided by the present invention is further described below with reference to examples and comparative examples.
Example 1
The embodiment 1 provides a flexible graphene-nano silicon composite film, which is prepared according to the following steps:
(A) preparation of graphene oxide Dispersion
(1) Measuring 160mL of H2SO4Adding 4g of graphite flake into a three-neck flask, stirring for 0.5h, and slowly adding 1.6g of KMnO at the temperature of 45 DEG C4And reacting for 24 hours.
(2) Slowly adding the reaction solution into a certain aqueous solution under the ice-bath condition, and dropwise adding a proper amount of H2O2Until the mixture turns brown-yellow, stirring for 2H, centrifuging, and adding 0.1M HCl and H respectively2And performing centrifugal washing for three times, and calculating the solid content of the graphene dispersion liquid.
(B) Preparation of nano-silica Dispersion having amino groups coupled to the surface
(1) Weighing 14.5mL of distilled water, 5mL of hydrochloric acid and 35mL of absolute ethyl alcohol, mixing, slowly dropwise adding 50mL of tetraethoxysilane under the stirring condition, stirring for 2 hours, filtering, washing with alcohol, and drying to obtain nano silicon dioxide powder;
(2) dispersing 1g of nano-silica powder into 100mL of dry xylene, performing ultrasonic treatment for 1h, adding 1mL of KH550, heating to 80 ℃, refluxing for 12h under the protection of inert gas, performing suction filtration, washing with absolute ethyl alcohol for multiple times, re-dispersing in absolute ethyl alcohol to obtain a nano-silica suspension with amino groups coupled on the surface, and calculating the solid content of the suspension.
(C) Preparation of flexible multilayer graphene/nano-silicon composite membrane
(1) Mixing a graphene oxide suspension and a nano-silica suspension with an amino group coupled on the surface according to a solid content ratio of 85:15, wherein the solvent ratio is 1:1 of a mixed solution of ethanol and distilled water, uniformly stirring, vertically adding a zinc sheet, reacting at normal temperature for 24 hours to obtain a deposited film, washing unreacted graphene on the surface with distilled water, and soaking the zinc sheet in the distilled water for 3 hours for freeze drying;
(2) scraping the deposited film off the chip completely by using a blade, soaking the film in 0.1M dilute hydrochloric acid for 3 hours, then soaking the film in distilled water, and performing freeze drying to obtain a flexible graphene oxide-nano silicon dioxide composite film;
(3) graphene oxide-nano silicon dioxide composite membrane in H2Carrying out hydrogenation reduction treatment at 800 ℃ for 12h in the presence of mixed gas of/Ar (the mixing ratio is 20:80) to obtain the flexible graphene-nano silicon composite membrane.
Example 2
This example 4 provides a flexible graphene-nano silicon composite film, which is prepared by a method different from that in example 1, in the step (C), the graphene oxide suspension and the nano silicon dioxide suspension having an amino group coupled to the surface are mixed according to a solid content of 95: 5, mixing in proportion; the rest steps and raw materials are the same as those in example 1, and are not described again.
Example 3
This example 3 provides a flexible graphene-nano silicon composite film, and the preparation method thereof is different from that in example 1, in the step (C), a graphene oxide suspension and a nano silicon dioxide suspension with an amino group coupled to the surface are mixed according to a solid content ratio of 70:30, and the remaining steps and raw materials are the same as those in example 1, and are not described herein again.
Example 4
This example 4 provides a flexible graphene-nano silicon composite film, which is prepared by a method different from that in example 1, in the step (C), the graphene oxide suspension and the nano silicon dioxide suspension having an amino group coupled to the surface are mixed according to a solid content of 90: 10, and the rest steps and raw materials are the same as those in example 1, and are not described again.
Example 5
This example 5 provides a flexible graphene-nano silicon composite film, which is prepared by a method different from that of example 1, in that, in the step (C), a graphene oxide suspension and a nano silicon dioxide suspension having an amino group coupled to a surface thereof are mixed in a solid content of 80: 20, and the rest steps and raw materials are the same as those in example 1, and are not described again.
Example 6
This example 4 provides a flexible graphene-nano silicon composite film, which is prepared by a method different from that in example 1, in the step (C), the graphene oxide suspension and the nano silicon dioxide suspension having an amino group coupled to the surface are mixed according to a solid content ratio of 99: 1, and the rest steps and raw materials are the same as those in example 1 and are not described again.
Example 7
This example 5 provides a flexible graphene-nano silicon composite film, which is prepared by a method different from that of example 1, in that, in the step (C), a graphene oxide suspension and a nano silicon dioxide suspension having an amino group coupled to a surface thereof are mixed in a solid content ratio of 50: 50, and the rest steps and raw materials are the same as those in example 1 and are not described again.
Comparative example 1
This comparative example 1 provides a nano-silicon having a particle size of 10 to 50 nm.
Test example 1
The flexible graphene-nano silicon composite film provided in example 1 was tested using Tecnai12-TEM manufactured by FEI corporation, the netherlands, at a voltage of 100KV and JEOL JEM 2010HRTEM manufactured by japan science corporation, at a voltage of 200KV, as shown in fig. 1, it can be seen from fig. 1 that the flexible graphene-nano silicon composite film provided in example 1 includes graphene sheets and nano silicon, wherein the nano silicon is coated in the graphene sheets, and the particle size of the nano silicon is 10 to 50 nm.
Test example 2
The flexible graphene-nano silicon composite film provided in example 1 was observed under a test voltage of 15kV at different magnifications using a Sigma type Scanning Electron Microscope (SEM) of national zeiss. As shown in fig. 2. As can be seen from fig. 2, the flexible-nano silicon composite film provided in example 1 includes nano silicon and graphene, and the graphene is a multilayer structure, wherein the nano silicon is coated in graphene sheets, and the particle size of the nano silicon is 10-50 nm.
Test example 3
The flexible graphene-nano silicon composite film provided in example 1 was tested by using an X-ray diffractometer model XD-2 from kyopuxin universal instruments ltd, a Cu-Ka target was used to generate a light source, 36KV high voltage, 30mV current, 0.15406nm wavelength, scanning speed of 10 °/min, scanning range of 20 ° -80 °, and the results are shown in fig. 3. As can be seen from fig. 3, the flexible graphene-nano silicon composite film provided in example 1 has distinct diffraction peaks at 2 θ angles of 26 °, 28.4 °, 47.3 °, and 56.1 °, which indicates that the flexible graphene-nano peak composite film provided in example 1 has graphene and silicon.
Test example 4 cycle performance test
The flexible graphene-nano silicon composite films provided in examples 1 to 7 were tested by using a new wiler BTS battery test system, respectively, with a test voltage range of 1V, a current density of 200mA/g, a test temperature of 25 ℃, and test results shown in table 1.
TABLE 1 lithium ion battery charging and discharging test data table
As can be seen from table 1, in the flexible graphene-nano silicon composite films provided in examples 1 to 5, as the proportion of the doped nano silicon in the composite film increases, the first charge capacity of the prepared lithium ion battery gradually increases, and particularly when the graphene oxide suspension is mixed with the nano silicon dioxide suspension with the surface coupled with amino groups according to the proportion of the solid content of 85:15, the prepared flexible graphene-nano silicon composite film has the best performance. When the solid content ratio of the graphene oxide suspension to the nano-silica suspension with the surface coupled with the amino group is lower than the ratio of 85:15, in the process of forming the flexible composite film, self-aggregation of nano-silicon occurs, the graphene cannot well coat the nano-silicon to form the flexible film, and the aggregated nano-silicon is easy to fall off in the subsequent soaking and washing process, so that the silicon content in the flexible composite film is reduced, and the charge-discharge capacity is reduced.
In addition, it can also be seen from the comparison between examples 1 to 5 and example 6 that, in the process of preparing the flexible graphene-nano silicon composite film, when the solid content ratio of the graphene oxide suspension to the nano silica suspension with the amino group coupled to the surface is higher than 95: and 5, because the content of the nano-silicon in the prepared flexible composite membrane is too low, the first charge capacity of the prepared lithium ion battery is lower than 410mAh/g, and when the solid content ratio of the graphene oxide suspension to the nano-silicon dioxide suspension with the surface coupled with amino groups is lower than 70: at 30, a flexible composite film cannot be produced.
It can be seen from comparison between examples 1 to 5 and comparative example 1 that, although the first charge capacity of the flexible graphene-nano silicon composite film is lower than that of nano silicon provided in comparative example 1 when the flexible graphene-nano silicon composite film is tested by using a new Wilbts battery test system, the capacity retention rate after 200 cycles of the flexible graphene-nano silicon composite film is far lower than that of examples 1 to 5, which indicates that the flexible graphene-nano silicon composite film not only reduces agglomeration of nano silicon by coating nano silicon in a graphene sheet layer, but also provides an effective buffer space for volume expansion of nano silicon by graphene, so that when the flexible graphene-nano silicon composite film is used as a negative electrode material of a lithium ion battery, the lithium storage specific capacity and the cycle performance can be effectively improved. In addition, fig. 4 and 5 are test curves of the flexible graphene-nano silicon composite film provided in examples 1 to 2, respectively, and it can be seen from both fig. 4 and 5 that the new wilr BTS battery test system using the flexible graphene-nano silicon composite film provided in examples 1 to 2 has good cycle performance.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (29)
1. A preparation method of a flexible graphene-nano silicon composite film is characterized by comprising the following steps:
(a) uniformly mixing nano silicon dioxide with positive charge groups loaded on the surface, graphene oxide and a metal sheet in a solvent, and carrying out redox reaction on the graphene oxide and the metal sheet to obtain a graphene oxide-nano silicon dioxide composite film loaded on the metal sheet;
(b) separating the metal sheet from the graphene oxide-nano silicon dioxide composite film to obtain a graphene oxide-nano silicon dioxide composite film;
(c) carrying out reduction treatment on the graphene oxide-nano silicon dioxide composite membrane to obtain a flexible graphene-nano silicon composite membrane;
the flexible graphene-nano silicon composite film comprises nano silicon and graphene, wherein the nano silicon is coated in a sheet layer of the graphene.
2. The method according to claim 1, wherein the graphene is a multilayer graphene.
3. The method according to claim 1, wherein the nano silicon has a particle size of 10 to 200 nm.
4. The method according to claim 1, wherein in the step (a), the solvent is a mixed solution of a lower alcohol and water.
5. The production method according to claim 4, wherein the solvent is a mixed solution of ethanol and water.
6. The method according to claim 5, wherein the volume ratio of ethanol to water is (1-2): (1-2).
7. The method according to claim 6, wherein the volume ratio of ethanol to water is 1: 1.
8. The preparation method according to claim 1, wherein the nanosilica with the surface loaded with the positive charge groups is prepared by coupling the nanosilica with a coupling agent with the positive charge groups.
9. The method of claim 8, wherein the positively charged group coupling agent is an aminosilane coupling agent.
10. The method according to claim 9, wherein the aminosilane coupling agent is at least one selected from the group consisting of γ -aminopropyltriethoxysilane, γ -aminopropyltrimethoxysilane, N- β (aminoethyl) - γ -aminopropylmethyldimethoxysilane, N- β (aminoethyl) - γ -aminopropyltriethoxysilane, phenylaminomethyltriethoxysilane, phenylaminomethyltrimethoxysilane, aminoethylaminopropyltrimethoxysilane, and polyaminoalkyltrialkoxysilanes.
11. The method of claim 10, wherein the aminosilane coupling agent is gamma-aminopropyltriethoxysilane.
12. The preparation method according to claim 1, wherein the mass ratio of the graphene oxide to the nano-silica is (70-95): (30-5).
13. The preparation method according to claim 12, wherein the mass ratio of the graphene oxide to the nano-silica is (80-90): (10-20).
14. The preparation method according to claim 12, wherein the mass ratio of the graphene oxide to the nano silicon dioxide is 85: 15.
15. The method of claim 1, wherein the metal sheet comprises at least one of an iron sheet, a magnesium sheet, a zinc sheet, an aluminum sheet, and a copper sheet.
16. The method of claim 1, wherein the metal sheet is a zinc sheet.
17. The method according to claim 1, wherein in the step (a), the redox reaction time is 8 to 16 hours.
18. The method according to claim 1, wherein in the step (a), the redox reaction time is 10 to 15 hours.
19. The method according to claim 1, wherein in the step (a), the redox reaction time is 12 hours.
20. The method according to claim 1, wherein in the step (c), the graphene oxide-nano silica composite membrane is subjected to high-temperature hydrogenation reduction treatment.
21. The method of claim 20, wherein in step (c), H is used2Carrying out high-temperature hydrogenation reduction treatment on the-Ar mixed gas.
22. The method of claim 21, wherein H is2In the mixed gas of-Ar, H2And Ar in a volume ratio of (5-20): (95-80).
23. The method of claim 21, wherein H is2In the mixed gas of-Ar, H2And Ar in a volume ratio of (10-20): (90-80).
24. The method of claim 21, wherein H is2In the mixed gas of-Ar, H2And Ar in a volume ratio of 20: 80.
25. The method as claimed in claim 20, wherein the temperature of the hydrogenation reduction is 700 ℃ and 900 ℃ and the time of the hydrogenation reduction is 10-15 h.
26. The method as claimed in claim 20, wherein the temperature of the hydrogenation reduction is 750-850 ℃, and the time of the hydrogenation reduction is 11-13 h.
27. The production method according to any one of claims 1 to 26, wherein the graphene oxide is formed by oxidation of a graphite sheet;
and/or the nano silicon dioxide is prepared by a precipitation method.
28. The application of the flexible graphene-nano silicon composite membrane obtained by the preparation method according to any one of claims 1 to 27 in a lithium ion battery anode material.
29. A lithium ion battery comprising the flexible graphene-nano silicon composite film obtained by the preparation method according to any one of claims 1 to 27.
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