CN113178544A - Spiral silicon/graphene composite cathode for lithium battery and preparation method - Google Patents

Spiral silicon/graphene composite cathode for lithium battery and preparation method Download PDF

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CN113178544A
CN113178544A CN202110388164.6A CN202110388164A CN113178544A CN 113178544 A CN113178544 A CN 113178544A CN 202110388164 A CN202110388164 A CN 202110388164A CN 113178544 A CN113178544 A CN 113178544A
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silicon
graphene
flexible substrate
spiral
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陈庆
廖健淞
司文彬
李钧
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Chengdu New Keli Chemical Science Co Ltd
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    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
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    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
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    • Y02E60/10—Energy storage using batteries

Abstract

The invention relates to the technical field of polymer electrolytes, in particular to a spiral silicon/graphene composite negative electrode for a lithium battery and a preparation method thereof. According to the invention, a copper nanowire film is prepared on the surface of a flexible substrate by using screen printing, the growth of a graphene band is promoted by using a copper catalyst, a nano silicon dispersion liquid is coated on the surface, the flexible substrate is twisted according to a spiral structure and then the copper nanowire is corroded to obtain the mutually intertwined spiral structure graphene band, the spiral structure graphene band is coated by using hydrolyzed silicon dioxide nanogel after ultrasonic dispersion, and the silicon dioxide coated spiral graphene/silicon nanoparticle composite negative electrode material is obtained after thermocuring treatment. The prepared cathode material is internally provided with the spiral graphene framework, so that a larger expansion space is provided for the volume change of silicon in the charging and discharging processes, the structural stability of the cathode material is ensured, and the cycle performance of the cathode material is improved.

Description

Spiral silicon/graphene composite cathode for lithium battery and preparation method
Technical Field
The invention relates to the technical field of polymer electrolytes, in particular to a spiral silicon/graphene composite negative electrode for a lithium battery and a preparation method thereof.
Background
With the rapid development of technology, the conventional lithium secondary battery cannot meet the requirement of high specific energy for new energy vehicles, mobile devices, and advanced energy storage devices. The lithium-sulfur battery with elemental sulfur as the positive electrode and metal lithium as the negative electrode has high specific energy density 2600Wh/kg, and the sulfur positive electrode has the advantages of low price, rich resources, environmental protection and the like, so the lithium-sulfur battery becomes one of the high-energy-density secondary batteries with application potential. The silicon negative electrode material has high specific capacity, the theoretical capacity of the silicon negative electrode material is up to 4200mAh/g, the silicon negative electrode material is environment-friendly and rich in reserve, silicon can play a role of a mechanical framework in the negative electrode in the charging and discharging process, lithium atoms are dispersed, the generation of lithium dendrites due to the interface enrichment of metal lithium is inhibited, the safety performance is high, and the silicon negative electrode material is a high-energy-density lithium-sulfur battery negative electrode material with wide application prospect.
In addition, one of the most widely used negative active materials of the lithium ion battery is a graphite material, and the theoretical specific capacity of the graphite material is only 372mAh/g, so that the improvement of the energy density of the battery is limited. Although the research and development results of the new negative active material do not lack high specific capacity materials, such as silicon-based negative materials, the theoretical specific capacity is up to 4200mAh/g, but the application prospect of the new negative active material is still not optimistic due to the volume change of the new negative active material in the using process and the like. One of the best solutions to solve the huge volume change of the silicon material in the charging and discharging processes is to prepare porous silicon and reserve the space for volume expansion. The typical method for preparing porous silicon is to combine silicon and silicon dioxide by the action of some templates, and then remove the silicon dioxide by the reaction of the silicon dioxide and hydrogen fluoride, wherein the original position of the silicon dioxide is the position of the gap of the porous silicon. A typical approach is porous silicon microspheres (nat. nanotechnol., 2014, 9, 187-.
On the other hand, as is known, most of silicon materials cannot be used as a negative electrode independently, and graphite/silicon composite (i.e. silicon carbon material in general) is often prepared by using graphite as an aggregate to be used as a negative electrode in practical application. However, the nano silicon particles are easy to agglomerate and cannot be directly compounded with graphite for use, and the silicon-carbon composite material compounded by the Si/C/G is often constructed so as to meet the requirements of the lithium ion battery on the first cycle coulomb efficiency and the cycle stability of the silicon-carbon composite material in the actual application process.
However, the volume change of the silicon negative electrode material is in a linear relationship with the lithium intercalation capacity, and the reversible capacity is in direct proportion to the volume expansion in the lithium storage process, so that the silicon negative electrode material inevitably faces large volume change while obtaining high capacity. The large volume change easily causes the poor structural stability of the silicon cathode. In addition, the silicon negative electrode material has large volume change in the circulation process to cause cracks and fall off, a fresh Si surface can be exposed in the electrolyte to continuously generate an SEI film, the continuous growth of the SEI film consumes a limited lithium source and the electrolyte, the capacity of the battery is continuously attenuated, the internal resistance is continuously increased, and the volume is correspondingly expanded.
Patent CN104662715B proposes a porous silicon-based negative electrode active material, a method for preparing the same, and a lithium secondary battery containing the same, in which silicon powder is pre-lithiated during the silicon-carbon compounding process, so that silicon particles are coated with carbon powder in the form of large particles, however, this method solves the problem of volume expansion of silicon powder, and simultaneously, the lithium ion transport efficiency of the particles is affected as the silicon powder and the carbon powder cannot be in close contact with each other.
Patent CN104334496B proposes hollow silicon particles, a preparation method thereof, and a negative electrode active material for lithium secondary battery comprising the hollow silicon particles, wherein silicon powder is loaded on a polymer template and then coated with carbon, the method also affects the contact and recombination performance of silicon and carbon, and gas generated by polymer decomposition greatly affects the carbon shell on the surface layer, so that silicon powder directly contacts with electrolyte to cause more side reactions. Therefore, the design of the hollow structure of the silicon-carbon cathode has very important practical significance.
In practical application, the continuous shrinkage and expansion of the silicon negative electrode material in the lithium desorption process easily causes the breakage of particles, so that the capacity is continuously reduced in the circulation process, and the volume expansion effect of more than 300% is accompanied. Meanwhile, an unstable SEI film on the silicon negative electrode is gradually thickened and polarized in the circulating process, and large mechanical stress is caused, so that the electrode structure is further damaged, the capacity attenuation of the battery is serious, and the service life of the battery is greatly reduced.
Disclosure of Invention
In view of the above disadvantages of the prior art, an object of the present invention is to provide a method for preparing a spiral silicon/graphene composite negative electrode for a lithium battery, which is used to solve the problems of the prior art that the volume change is large in the circulation process of a silicon negative electrode material, which results in the continuous growth of an SEI film and the severe attenuation of battery capacity, and at the same time, the present invention also provides a spiral silicon/graphene composite negative electrode for a lithium battery; a copper nanowire film is prepared on the surface of a flexible substrate through screen printing, growth of a graphene belt is promoted through a copper catalyst, a nano silicon dispersion liquid is coated on the surface, the flexible substrate is twisted according to a spiral structure, then copper nanowires are corroded, the mutually-intertwined spiral structure graphene belt is obtained, hydrolyzed silicon dioxide nanogel is used for coating after ultrasonic dispersion, and the silicon dioxide-coated spiral graphene/silicon nanoparticle composite negative electrode material is obtained after thermocuring treatment, so that the cycle performance of the negative electrode material is remarkably improved.
In order to attain the above and other related objects,
the invention provides a preparation method of a spiral silicon/graphene composite negative electrode for a lithium battery, which comprises the following steps:
mixing hydroxypropyl methyl cellulose, copper nanowires, propylene glycol, a surfactant and a defoaming agent in deionized water to prepare slurry, flattening the substrate by using a flexible film containing a nickel-chromium alloy coating as a substrate, fixing the flattened substrate on a screen printing machine, printing the slurry on the surface of the flexible substrate according to a pattern, and drying in vacuum to obtain the flexible substrate loaded with the copper nanowires;
fixing the flexible substrate obtained in the step one in a vacuum deposition chamber, and depositing graphene under the catalysis of the copper nanowires by using methane and hydrogen as gas sources to obtain a flexible substrate on which a graphene strip is deposited;
step three, adding nano silicon powder into deionized water, adding a small amount of dispersant and thickener for ultrasonic treatment to obtain nano silicon dispersed slurry, and coating the slurry on the surface of the flexible substrate with the graphene belt obtained in the step two;
step four, subjecting the flexible substrate obtained in the step three to vacuum drying and thermosetting, twisting the flexible substrate according to a spiral structure, fixing the twisted substrate, corroding the flexible substrate by using a ferric trichloride corrosive liquid, unfolding the flexible substrate after the corrosion is finished, adding a deionized water solution for ultrasonic dispersion, taking out the flexible substrate, and filtering and drying to obtain the spiral graphene loaded with the nano silicon particles;
and step five, adding the helical graphene loaded with the nano-silicon particles obtained in the step four into an ethyl orthosilicate aqueous solution, adjusting the pH to acidity for hydrolysis, performing silica gel coating, and finally performing heat treatment in a vacuum furnace to obtain the composite cathode material of the helical graphene/silicon nano-particles coated with silica.
The silicon/graphene composite negative electrode of the spiral frame is prepared by preparing a copper nanowire film on the surface of a flexible substrate through screen printing, promoting the growth of a graphene band through a copper catalyst, coating a nano silicon dispersion liquid on the surface, twisting the flexible substrate according to a spiral structure, corroding the copper nanowire to obtain the mutually-intertwined spiral structure graphene band, coating the flexible substrate with hydrolyzed silicon dioxide nanogel after ultrasonic dispersion, and obtaining the silicon dioxide coated spiral graphene/silicon nanoparticle composite negative electrode material after thermocuring treatment.
According to the invention, as the graphene belt grows on the surface of the copper nanowire, the graphene on the surfaces of different copper nanowires is broken by the twisting force, so that the copper nanowire-loaded graphene with the spiral structure is formed, the graphene is separated under the action of ferric trichloride corrosive liquid, the flexible substrate is unfolded and restored to be flat, the graphene keeps the spiral structure to be stripped by ultrasound, the graphene with the spiral structure is easy to intertwine with each other, and finally, the graphene is coated by silicon dioxide to form particles.
In an embodiment of the present invention, in the first step, the flexible substrate is a high temperature resistant inorganic flexible substrate, preferably a woven glass fiber fabric.
In an embodiment of the present invention, in the step one, the weight parts of the raw materials are as follows: 1-4 parts of hydroxypropyl methyl cellulose, 0.5-4 parts of copper nanowires, 1-3 parts of propylene glycol, 1-3 parts of a surfactant, 1-3 parts of a defoaming agent and 15-20 parts of deionized water.
In an embodiment of the invention, the thickness of the deposited graphene in the second step is 100-500 nm; the deposition temperature is 900-1100 ℃.
In an embodiment of the invention, in step three, the dispersant is PVP30, the thickener is sodium carboxymethyl cellulose, and the addition mass ratio of PVP30 to sodium carboxymethyl cellulose is 0.5-2: 5-10;
the solid content of the nano silicon dispersion slurry is 15-25%;
the slurry is coated by one of spraying, blade coating and roller coating, and the coating thickness is 10-20 um.
In an embodiment of the invention, the thermal curing in the fourth step is thermal curing in a muffle furnace at normal pressure, and the thermal processing temperature is 300-350 ℃.
In an embodiment of the invention, the formula of the ferric trichloride corrosive liquid in the fourth step is as follows by weight: 500-600 parts of ferric trichloride, 20-100 parts of hydrochloric acid and 1000 parts of water;
the corrosion temperature of the ferric trichloride corrosion solution is 40-60 ℃.
In an embodiment of the present invention, the pH of the hydrolysis of tetraethoxysilane in the step five is 3 to 5;
the vacuum heat treatment temperature is 400-600 ℃, and the treatment atmosphere is hydrogen or argon.
According to experimental tests, the conductivity of the silicon/graphene composite cathode of the spiral frame prepared by the preparation method is obviously improved, and the preparation method is characterized in that a copper nanowire film is prepared, graphene grows on the surface of the copper nanowire film, then a mutually-interlaced graphene belt with a spiral structure is obtained through spiral, a nano silicon dispersion liquid is coated on the copper nanowire loaded with the graphene, the copper nanowire film is coated by hydrolyzed silicon dioxide nanogel, and the silicon dioxide-coated composite cathode material of the spiral graphene/silicon nanoparticle is obtained after thermocuring treatment. According to the preparation method, the silicon/graphene composite cathode of the spiral frame is obtained by obtaining the graphene with the spiral structure and coating the surface of the graphene with silicon dioxide, and the preparation method is simple and can be processed in a large scale.
The silicon/graphene composite cathode with the spiral framework prepared by the preparation method has good interface stability and high conductivity.
In a second aspect of the present invention, a spiral silicon/graphene composite negative electrode for a lithium battery is provided, wherein the silicon/graphene composite negative electrode of the spiral frame is prepared by the above preparation method.
As described above, the spiral silicon/graphene composite negative electrode for the lithium battery, the preparation method thereof and the lithium battery provided by the invention have the following beneficial effects:
1. according to the invention, as the graphene belt grows on the surface of the copper nanowire, the graphene on the surfaces of different copper nanowires is broken by the twisting force, so that the copper nanowire-loaded graphene with the spiral structure is formed, the graphene is separated under the action of ferric trichloride corrosive liquid, the flexible substrate is unfolded and restored to be flat, the graphene keeps the spiral structure to be stripped by ultrasound, the graphene with the spiral structure is easy to intertwine with each other, and finally, the graphene is coated by silicon dioxide to form particles.
2. Through experimental tests, the conductivity of the silicon/graphene composite cathode with the spiral framework prepared by the preparation method is obviously improved, and the reason is that the preparation method increases the composite interface of graphene and silicon dioxide. In addition, the nano-silicon dispersion liquid is coated on the surface of the copper nanowire film, then the graphene band with the spiral structure which is mutually intertwined is obtained through spiral, the hydrolyzed silicon dioxide nanogel is coated, and the composite negative electrode material of the silicon dioxide coated spiral graphene/silicon nanoparticles is obtained after thermocuring treatment. According to the preparation method, the silicon/graphene composite cathode of the spiral frame is obtained by obtaining the graphene with the spiral structure and coating the surface of the graphene with silicon dioxide, and the preparation method is simple and can be processed in a large scale.
3. The spiral graphene in the silicon/graphene composite negative electrode of the spiral frame serves as the frame, a larger expansion space is provided for silicon volume change in the charging and discharging processes, the structural stability of the negative electrode material is guaranteed, and the cycle performance of the negative electrode material is improved. Meanwhile, the silicon dioxide coating on the surface can effectively isolate the direct contact between the nano silicon and the electrolyte, thereby improving the cycle performance of the lithium battery.
Drawings
FIG. 1 is a schematic illustration of a flexible substrate according to the present invention distorted;
FIG. 2 is a schematic diagram of the structure of a sample according to the present invention, namely graphene, 2 nano-silicon particles and 3 silica gel;
FIG. 3 is a process flow diagram of the present invention;
FIG. 4 is a photograph of a density test of example 1;
fig. 5 is a photograph of a density test of comparative example 1.
Detailed Description
The present invention will be described in further detail with reference to specific embodiments, but it should not be construed that the scope of the present invention is limited to the following examples. Various substitutions and alterations can be made by those skilled in the art and by conventional means without departing from the spirit of the method of the invention described above.
Example 1
A preparation method of a spiral silicon/graphene composite negative electrode for a lithium battery comprises the following steps:
mixing hydroxypropyl methyl cellulose, copper nanowires, propylene glycol, a surfactant and a defoaming agent in deionized water to prepare slurry, flattening the substrate by using a flexible film containing a nickel-chromium alloy coating as a substrate, fixing the flattened substrate on a screen printing machine, printing the slurry on the surface of the flexible substrate according to a pattern, and drying in vacuum to obtain the flexible substrate loaded with the copper nanowires; the flexible substrate is glass fiber woven cloth; the weight parts of the raw materials are as follows: 3 parts of hydroxypropyl methyl cellulose, 2 parts of copper nanowires, 2 parts of propylene glycol, 2 parts of a surfactant, 2 parts of a defoaming agent and 18 parts of deionized water;
fixing the flexible substrate obtained in the step one in a vacuum deposition chamber, and depositing graphene under the catalysis of copper nanowires by using methane and hydrogen as gas sources to obtain a flexible substrate for depositing a graphene band, wherein the thickness of the deposited graphene is 300nm, and the deposition temperature is 1000 ℃;
step three, adding nano silicon powder into deionized water, adding a small amount of dispersant and thickener for ultrasonic treatment to obtain nano silicon dispersed slurry with the solid content of 20%, and coating the slurry on the surface of the flexible substrate with the graphene belt obtained in the step two; the dispersing agent is PVP30, the thickening agent is sodium carboxymethyl cellulose, and the adding mass ratio of PVP30 to sodium carboxymethyl cellulose is 1: 8; the slurry is coated in a spraying mode, and the coating thickness is 15 um;
step four, subjecting the flexible substrate obtained in the step three to vacuum drying and thermosetting, twisting the flexible substrate according to a spiral structure, fixing the twisted substrate, corroding the flexible substrate by using a ferric trichloride corrosive liquid, unfolding the flexible substrate after the corrosion is finished, adding a deionized water solution for ultrasonic dispersion, taking out the flexible substrate, and filtering and drying to obtain the spiral graphene loaded with the nano silicon particles; the thermal curing treatment is normal-pressure muffle furnace thermal treatment curing, and the thermal treatment temperature is 330 ℃; the formula of the ferric trichloride corrosive liquid comprises the following components in parts by weight: 550 parts of ferric trichloride, 60 parts of hydrochloric acid and 1000 parts of water; the corrosion temperature is 50 ℃;
and step five, adding the helical graphene loaded with the nano-silicon particles obtained in the step four into an ethyl orthosilicate aqueous solution, adjusting the pH to acidity for hydrolysis, carrying out silicon dioxide gel coating, and finally carrying out heat treatment in a vacuum furnace at the temperature of 500 ℃ in the presence of hydrogen to obtain the silicon dioxide coated helical graphene/silicon nano-particle composite negative electrode material.
Example 2
A preparation method of a spiral silicon/graphene composite negative electrode for a lithium battery comprises the following steps:
mixing hydroxypropyl methyl cellulose, copper nanowires, propylene glycol, a surfactant and a defoaming agent in deionized water to prepare slurry, flattening the substrate by using a flexible film containing a nickel-chromium alloy coating as a substrate, fixing the flattened substrate on a screen printing machine, printing the slurry on the surface of the flexible substrate according to a pattern, and drying in vacuum to obtain the flexible substrate loaded with the copper nanowires; the flexible substrate is glass fiber woven cloth; the weight parts of the raw materials are as follows: 1 part of hydroxypropyl methyl cellulose, 0.5 part of copper nanowire, 3 parts of propylene glycol, 3 parts of surfactant, 3 parts of defoaming agent and 20 parts of deionized water;
fixing the flexible substrate obtained in the step one in a vacuum deposition chamber, and depositing graphene under the catalysis of copper nanowires by using methane and hydrogen as gas sources to obtain a flexible substrate for depositing a graphene strip, wherein the thickness of the deposited graphene is 500nm, and the deposition temperature is 900 ℃;
step three, adding nano silicon powder into deionized water, adding a small amount of dispersant and thickener for ultrasonic treatment to obtain nano silicon dispersed slurry with the solid content of 25%, and coating the slurry on the surface of the flexible substrate with the graphene belt obtained in the step two; the dispersing agent is PVP30, the thickening agent is sodium carboxymethyl cellulose, and the addition mass ratio of PVP30 to sodium carboxymethyl cellulose is 0.5: 5; the slurry is coated in a blade coating mode, and the coating thickness is 20 microns;
step four, subjecting the flexible substrate obtained in the step three to vacuum drying and thermosetting, twisting the flexible substrate according to a spiral structure, fixing the twisted substrate, corroding the flexible substrate by using a ferric trichloride corrosive liquid, unfolding the flexible substrate after the corrosion is finished, adding a deionized water solution for ultrasonic dispersion, taking out the flexible substrate, and filtering and drying to obtain the spiral graphene loaded with the nano silicon particles; the thermal curing treatment is normal-pressure muffle furnace thermal treatment curing, and the thermal treatment temperature is 350 ℃; the formula of the ferric trichloride corrosive liquid comprises the following components in parts by weight: 600 parts of ferric trichloride, 100 parts of hydrochloric acid and 1000 parts of water; the corrosion temperature is 40 ℃;
and step five, adding the helical graphene loaded with the nano-silicon particles obtained in the step four into an ethyl orthosilicate aqueous solution, adjusting the pH to acidity for hydrolysis, carrying out silicon dioxide gel coating, and finally carrying out heat treatment in a vacuum furnace at the temperature of 400 ℃ in argon atmosphere to obtain the silicon dioxide coated helical graphene/silicon nano-particle composite negative electrode material.
Example 3
A preparation method of a spiral silicon/graphene composite negative electrode for a lithium battery comprises the following steps:
mixing hydroxypropyl methyl cellulose, copper nanowires, propylene glycol, a surfactant and a defoaming agent in deionized water to prepare slurry, flattening the substrate by using a flexible film containing a nickel-chromium alloy coating as a substrate, fixing the flattened substrate on a screen printing machine, printing the slurry on the surface of the flexible substrate according to a pattern, and drying in vacuum to obtain the flexible substrate loaded with the copper nanowires; the flexible substrate is glass fiber woven cloth; the weight parts of the raw materials are as follows: 4 parts of hydroxypropyl methyl cellulose, 4 parts of copper nanowires, 1 part of propylene glycol, 2 parts of a surfactant, 3 parts of a defoaming agent and 20 parts of deionized water;
fixing the flexible substrate obtained in the step one in a vacuum deposition chamber, and depositing graphene under the catalysis of copper nanowires by using methane and hydrogen as gas sources to obtain a flexible substrate for depositing a graphene strip, wherein the thickness of the deposited graphene is 500nm, and the deposition temperature is 1100 ℃;
step three, adding nano silicon powder into deionized water, adding a small amount of dispersant and thickener for ultrasonic treatment to obtain nano silicon dispersed slurry with solid content of 15%, and coating the slurry on the surface of the flexible substrate with the graphene belt obtained in the step two; the dispersing agent is PVP30, the thickening agent is sodium carboxymethyl cellulose, and the addition mass ratio of PVP30 to sodium carboxymethyl cellulose is 1: 9; the slurry is coated by roller coating, and the coating thickness is 20 um;
step four, subjecting the flexible substrate obtained in the step three to vacuum drying and thermosetting, twisting the flexible substrate according to a spiral structure, fixing the twisted substrate, corroding the flexible substrate by using a ferric trichloride corrosive liquid, unfolding the flexible substrate after the corrosion is finished, adding a deionized water solution for ultrasonic dispersion, taking out the flexible substrate, and filtering and drying to obtain the spiral graphene loaded with the nano silicon particles; the thermal curing treatment is normal-pressure muffle furnace thermal treatment curing, and the thermal treatment temperature is 320 ℃; the formula of the ferric trichloride corrosive liquid comprises the following components in parts by weight: 600 parts of ferric trichloride, 80 parts of hydrochloric acid and 1000 parts of water; the corrosion temperature is 60 ℃;
and step five, adding the helical graphene loaded with the nano-silicon particles obtained in the step four into an ethyl orthosilicate aqueous solution, adjusting the pH to acidity for hydrolysis, carrying out silicon dioxide gel coating, and finally carrying out heat treatment in a vacuum furnace at the temperature of 450 ℃ in the presence of hydrogen to obtain the silicon dioxide coated helical graphene/silicon nano-particle composite negative electrode material.
Example 4
A preparation method of a spiral silicon/graphene composite negative electrode for a lithium battery comprises the following steps:
mixing hydroxypropyl methyl cellulose, copper nanowires, propylene glycol, a surfactant and a defoaming agent in deionized water to prepare slurry, flattening the substrate by using a flexible film containing a nickel-chromium alloy coating as a substrate, fixing the flattened substrate on a screen printing machine, printing the slurry on the surface of the flexible substrate according to a pattern, and drying in vacuum to obtain the flexible substrate loaded with the copper nanowires; the flexible substrate is glass fiber woven cloth; the weight parts of the raw materials are as follows: 3 parts of hydroxypropyl methyl cellulose, 2 parts of copper nanowires, 1 part of propylene glycol, 3 parts of a surfactant, 2 parts of a defoaming agent and 18 parts of deionized water;
fixing the flexible substrate obtained in the step one in a vacuum deposition chamber, and depositing graphene under the catalysis of copper nanowires by using methane and hydrogen as gas sources to obtain a flexible substrate for depositing a graphene band, wherein the thickness of the deposited graphene is 300nm, and the deposition temperature is 1000 ℃;
step three, adding nano silicon powder into deionized water, adding a small amount of dispersant and thickener for ultrasonic treatment to obtain nano silicon dispersed slurry with the solid content of 20%, and coating the slurry on the surface of the flexible substrate with the graphene belt obtained in the step two; the dispersing agent is PVP30, the thickening agent is sodium carboxymethyl cellulose, and the adding mass ratio of PVP30 to sodium carboxymethyl cellulose is 0.5: 7; the slurry is coated in a spraying mode, and the coating thickness is 13 um;
step four, subjecting the flexible substrate obtained in the step three to vacuum drying and thermosetting, twisting the flexible substrate according to a spiral structure, fixing the twisted substrate, corroding the flexible substrate by using a ferric trichloride corrosive liquid, unfolding the flexible substrate after the corrosion is finished, adding a deionized water solution for ultrasonic dispersion, taking out the flexible substrate, and filtering and drying to obtain the spiral graphene loaded with the nano silicon particles; the thermal curing treatment is normal-pressure muffle furnace thermal treatment curing, and the thermal treatment temperature is 340 ℃; the formula of the ferric trichloride corrosive liquid comprises the following components in parts by weight: 560 parts of ferric trichloride, 70 parts of hydrochloric acid and 1000 parts of water; the corrosion temperature is 55 ℃;
and step five, adding the helical graphene loaded with the nano-silicon particles obtained in the step four into an ethyl orthosilicate aqueous solution, adjusting the pH to acidity for hydrolysis, carrying out silicon dioxide gel coating, and finally carrying out heat treatment in a vacuum furnace at the temperature of 500 ℃ in argon atmosphere to obtain the silicon dioxide coated helical graphene/silicon nano-particle composite negative electrode material.
Example 5
A preparation method of a spiral silicon/graphene composite negative electrode for a lithium battery comprises the following steps:
mixing hydroxypropyl methyl cellulose, copper nanowires, propylene glycol, a surfactant and a defoaming agent in deionized water to prepare slurry, flattening the substrate by using a flexible film containing a nickel-chromium alloy coating as a substrate, fixing the flattened substrate on a screen printing machine, printing the slurry on the surface of the flexible substrate according to a pattern, and drying in vacuum to obtain the flexible substrate loaded with the copper nanowires; the flexible substrate is glass fiber woven cloth; the weight parts of the raw materials are as follows: 3 parts of hydroxypropyl methyl cellulose, 2 parts of copper nanowires, 3 parts of propylene glycol, 3 parts of a surfactant, 1 part of a defoaming agent and 19 parts of deionized water;
fixing the flexible substrate obtained in the step one in a vacuum deposition chamber, and depositing graphene under the catalysis of copper nanowires by using methane and hydrogen as gas sources to obtain a flexible substrate for depositing a graphene band, wherein the thickness of the deposited graphene is 350nm, and the deposition temperature is 950 ℃;
step three, adding nano silicon powder into deionized water, adding a small amount of dispersant and thickener for ultrasonic treatment to obtain nano silicon dispersed slurry with the solid content of 22%, and coating the slurry on the surface of the flexible substrate with the graphene belt obtained in the step two; the dispersing agent is PVP30, the thickening agent is sodium carboxymethyl cellulose, and the addition mass ratio of PVP30 to sodium carboxymethyl cellulose is 1: 9; the slurry is coated by roller coating, and the coating thickness is 18 um;
step four, subjecting the flexible substrate obtained in the step three to vacuum drying and thermosetting, twisting the flexible substrate according to a spiral structure, fixing the twisted substrate, corroding the flexible substrate by using a ferric trichloride corrosive liquid, unfolding the flexible substrate after the corrosion is finished, adding a deionized water solution for ultrasonic dispersion, taking out the flexible substrate, and filtering and drying to obtain the spiral graphene loaded with the nano silicon particles; the thermal curing treatment is normal-pressure muffle furnace thermal treatment curing, and the thermal treatment temperature is 340 ℃; the formula of the ferric trichloride corrosive liquid comprises the following components in parts by weight: 570 parts of ferric trichloride, 90 parts of hydrochloric acid and 1000 parts of water; the corrosion temperature is 55 ℃;
and step five, adding the helical graphene loaded with the nano-silicon particles obtained in the step four into an ethyl orthosilicate aqueous solution, adjusting the pH to acidity for hydrolysis, carrying out silicon dioxide gel coating, and finally carrying out heat treatment in a vacuum furnace at 550 ℃ in the presence of hydrogen to obtain the silicon dioxide coated helical graphene/silicon nano-particle composite negative electrode material.
Example 6
A preparation method of a spiral silicon/graphene composite negative electrode for a lithium battery comprises the following steps:
mixing hydroxypropyl methyl cellulose, copper nanowires, propylene glycol, a surfactant and a defoaming agent in deionized water to prepare slurry, flattening the substrate by using a flexible film containing a nickel-chromium alloy coating as a substrate, fixing the flattened substrate on a screen printing machine, printing the slurry on the surface of the flexible substrate according to a pattern, and drying in vacuum to obtain the flexible substrate loaded with the copper nanowires; the flexible substrate is glass fiber woven cloth; the weight parts of the raw materials are as follows: 2 parts of hydroxypropyl methyl cellulose, 3 parts of copper nanowires, 3 parts of propylene glycol, 2 parts of a surfactant, 3 parts of a defoaming agent and 17 parts of deionized water;
fixing the flexible substrate obtained in the step one in a vacuum deposition chamber, and depositing graphene under the catalysis of copper nanowires by using methane and hydrogen as gas sources to obtain a flexible substrate for depositing a graphene strip, wherein the thickness of the deposited graphene is 350nm, and the deposition temperature is 1050 ℃;
step three, adding nano silicon powder into deionized water, adding a small amount of dispersant and thickener for ultrasonic treatment to obtain nano silicon dispersed slurry with the solid content of 20%, and coating the slurry on the surface of the flexible substrate with the graphene belt obtained in the step two; the dispersing agent is PVP30, the thickening agent is sodium carboxymethyl cellulose, and the addition mass ratio of PVP30 to sodium carboxymethyl cellulose is 2: 9; the slurry is coated in a blade coating mode, and the coating thickness is 17 um;
step four, subjecting the flexible substrate obtained in the step three to vacuum drying and thermosetting, twisting the flexible substrate according to a spiral structure, fixing the twisted substrate, corroding the flexible substrate by using a ferric trichloride corrosive liquid, unfolding the flexible substrate after the corrosion is finished, adding a deionized water solution for ultrasonic dispersion, taking out the flexible substrate, and filtering and drying to obtain the spiral graphene loaded with the nano silicon particles; the thermal curing treatment is normal-pressure muffle furnace thermal treatment curing, and the thermal treatment temperature is 340 ℃; the formula of the ferric trichloride corrosive liquid comprises the following components in parts by weight: 540 parts of ferric trichloride, 80 parts of hydrochloric acid and 1000 parts of water; the corrosion temperature is 50 ℃;
and step five, adding the helical graphene loaded with the nano-silicon particles obtained in the step four into an ethyl orthosilicate aqueous solution, adjusting the pH to acidity for hydrolysis, carrying out silicon dioxide gel coating, and finally carrying out heat treatment in a vacuum furnace at 550 ℃ in the presence of hydrogen to obtain the silicon dioxide coated helical graphene/silicon nano-particle composite negative electrode material.
Comparative example 1
A preparation method of a spiral silicon/graphene composite negative electrode for a lithium battery comprises the following steps:
adding graphene nanosheets and nano silicon powder into deionized water, adding a small amount of dispersing agent and thickening agent for ultrasonic treatment to obtain mixed slurry of graphene and silicon powder, and coating the mixed slurry on the surface of a copper mesh; the dispersing agent is PVP30, the thickening agent is sodium carboxymethyl cellulose, and the addition mass ratio of PVP30 to sodium carboxymethyl cellulose is 2: 9; the slurry is coated in a blade coating mode, and the coating thickness is 17 um;
step two, subjecting the copper net coated with the mixed slurry obtained in the step one to vacuum drying and thermosetting, twisting according to a spiral structure, fixing the twisted substrate, corroding by using a ferric trichloride corrosive liquid, unfolding the flexible substrate copper net after the corrosion is finished, adding a deionized water solution for ultrasonic dispersion, taking out the flexible substrate copper net, and filtering and drying to obtain the spiral graphene loaded with nano silicon particles; the thermal curing treatment is normal-pressure muffle furnace thermal treatment curing, and the thermal treatment temperature is 340 ℃; the formula of the ferric trichloride corrosive liquid comprises the following components in parts by weight: 540 parts of ferric trichloride, 80 parts of hydrochloric acid and 1000 parts of water; the corrosion temperature is 50 ℃;
and step three, adding the helical graphene loaded with the nano-silicon particles obtained in the step two into an ethyl orthosilicate aqueous solution, adjusting the pH to acidity for hydrolysis, carrying out silicon dioxide gel coating, and finally carrying out heat treatment in a vacuum furnace at 550 ℃ in the presence of hydrogen to obtain the silicon dioxide coated helical graphene/silicon nano-particle composite negative electrode material.
The difference between the comparative example 1 and the example 6 is that in the comparative example 1, a graphene sheet and silicon powder are directly mixed and then coated on the surface of a flexible substrate copper mesh to obtain the silicon dioxide coated spiral graphene/silicon nanoparticle composite negative electrode material.
Comparative example 2
A preparation method of a silicon/graphene composite negative electrode for a lithium battery comprises the following steps:
mixing hydroxypropyl methyl cellulose, copper nanowires, propylene glycol, a surfactant and a defoaming agent in deionized water to prepare slurry, flattening the substrate by using a flexible film containing a nickel-chromium alloy coating as a substrate, fixing the flattened substrate on a screen printing machine, printing the slurry on the surface of the flexible substrate according to a pattern, and drying in vacuum to obtain the flexible substrate loaded with the copper nanowires; the flexible substrate is glass fiber woven cloth; the weight parts of the raw materials are as follows: 2 parts of hydroxypropyl methyl cellulose, 3 parts of copper nanowires, 3 parts of propylene glycol, 2 parts of a surfactant, 3 parts of a defoaming agent and 17 parts of deionized water;
fixing the flexible substrate obtained in the step one in a vacuum deposition chamber, and depositing graphene under the catalysis of copper nanowires by using methane and hydrogen as gas sources to obtain a flexible substrate for depositing a graphene strip, wherein the thickness of the deposited graphene is 350nm, and the deposition temperature is 1050 ℃;
step three, adding nano silicon powder into deionized water, adding a small amount of dispersant and thickener for ultrasonic treatment to obtain nano silicon dispersed slurry with the solid content of 20%, and coating the slurry on the surface of the flexible substrate with the graphene belt obtained in the step two; the dispersing agent is PVP30, the thickening agent is sodium carboxymethyl cellulose, and the addition mass ratio of PVP30 to sodium carboxymethyl cellulose is 2: 9; the slurry is coated in a blade coating mode, and the coating thickness is 17 um;
step four, carrying out vacuum drying and thermosetting on the flexible substrate obtained in the step three, corroding the flexible substrate by using a ferric trichloride corrosive liquid, adding a deionized water solution for ultrasonic dispersion after the corrosion is finished, taking out the flexible substrate, and filtering and drying to obtain the graphene loaded with the nano silicon particles; the thermal curing treatment is normal-pressure muffle furnace thermal treatment curing, and the thermal treatment temperature is 340 ℃; the formula of the ferric trichloride corrosive liquid comprises the following components in parts by weight: 540 parts of ferric trichloride, 80 parts of hydrochloric acid and 1000 parts of water; the corrosion temperature is 50 ℃;
and step five, adding the graphene loaded with the nano-silicon particles obtained in the step four into an ethyl orthosilicate aqueous solution, adjusting the pH to acidity for hydrolysis, carrying out silicon dioxide gel coating, and finally carrying out heat treatment in a vacuum furnace at 550 ℃ in the presence of hydrogen to obtain the silicon dioxide coated graphene/silicon nano-particle composite negative electrode material.
Comparative example 2 is different from example 6 in that the flexible substrate loaded with graphene is not subjected to the spiral twist process in comparative example 2.
Comparative example 3
A preparation method of a spiral silicon/graphene composite negative electrode for a lithium battery comprises the following steps:
mixing hydroxypropyl methyl cellulose, copper nanowires, propylene glycol, a surfactant and a defoaming agent in deionized water to prepare slurry, flattening the substrate by using a flexible film containing a nickel-chromium alloy coating as a substrate, fixing the flattened substrate on a screen printing machine, printing the slurry on the surface of the flexible substrate according to a pattern, and drying in vacuum to obtain the flexible substrate loaded with the copper nanowires; the flexible substrate is glass fiber woven cloth; the weight parts of the raw materials are as follows: 2 parts of hydroxypropyl methyl cellulose, 3 parts of copper nanowires, 3 parts of propylene glycol, 2 parts of a surfactant, 3 parts of a defoaming agent and 17 parts of deionized water;
fixing the flexible substrate obtained in the step one in a vacuum deposition chamber, and depositing graphene under the catalysis of copper nanowires by using methane and hydrogen as gas sources to obtain a flexible substrate for depositing a graphene strip, wherein the thickness of the deposited graphene is 350nm, and the deposition temperature is 1050 ℃;
step three, adding nano silicon powder into deionized water, adding a small amount of dispersant and thickener for ultrasonic treatment to obtain nano silicon dispersed slurry with the solid content of 20%, and coating the slurry on the surface of the flexible substrate with the graphene belt obtained in the step two; the dispersing agent is PVP30, the thickening agent is sodium carboxymethyl cellulose, and the addition mass ratio of PVP30 to sodium carboxymethyl cellulose is 2: 9; the slurry is coated in a blade coating mode, and the coating thickness is 17 um;
step four, subjecting the flexible substrate obtained in the step three to vacuum drying and thermosetting, twisting the flexible substrate according to a spiral structure, fixing the twisted substrate, corroding the flexible substrate by using a ferric trichloride corrosive liquid, unfolding the flexible substrate after the corrosion is finished, adding a deionized water solution for ultrasonic dispersion, taking out the flexible substrate, and filtering and drying to obtain the spiral graphene loaded with the nano silicon particles; the thermal curing treatment is normal-pressure muffle furnace thermal treatment curing, and the thermal treatment temperature is 340 ℃; the formula of the ferric trichloride corrosive liquid comprises the following components in parts by weight: 540 parts of ferric trichloride, 80 parts of hydrochloric acid and 1000 parts of water; the corrosion temperature is 50 ℃;
and fifthly, carrying out heat treatment on the spiral graphene loaded with the nano silicon particles obtained in the fourth step in a vacuum furnace at the temperature of 550 ℃ in the presence of hydrogen to obtain the composite anode material of the spiral graphene/silicon nanoparticles.
Comparative example 3 differs from example 6 in that no surface silica gel coating was performed in comparative example 3.
Performance testing
1. The negative electrode materials obtained in examples 1 to 6 and comparative examples 1 to 3 were prepared as a slurry with PVDF binder and super-P conductive agent in deionized water at a ratio of 8:1:1, coated on the surface of copper foil as a positive electrode, a lithium sheet as a negative electrode, lithium hexafluorophosphate/ethylene carbonate as an electrolyte, and celgard2400 as a separator, assembled into a CR2032 button cell in a glove box, and the cell was tested for cycle performance in a novice cell tester with a test current density of 0.4mA/g (about 0.3C) for 100 cycles. The test results are shown in table 1.
2. 100g of each of the powders of examples 1 to 6 and comparative examples 1 to 3 was weighed, and added to 300g of deionized water to prepare a dispersion, and the volume change of the solution before and after the addition was recorded to calculate the density of the powder.
Table form
Figure DEST_PATH_IMAGE002
First discharge capacity (mah/g) 100-cycle capacity loss (%) Powder Density (g/cm 3)
Example 1 665.8 13.6 0.674
Example 2 663.4 13.8 0.673
Example 3 666.2 14.3 0.670
Example 4 663.7 14.1 0.677
Example 5 660.6 13.9 0.675
Example 6 665.8 14.2 0.669
Comparative example 1 648.4 44.3 1.333
Comparative example 2 660.5 28.9 0.795
Comparative example 3 657.3 32.1 1.006
As can be seen from the data in the table 1, the first discharge capacities of the examples 1 to 6 are 663 to 667, which are obviously superior to the first discharge capacities of the comparative examples 1 to 3; therefore, the first discharge capacity of the silicon/graphene composite cathode with the spiral framework prepared by the preparation method is obviously improved. The capacity loss of the batteries of the embodiments 1 to 6 is only about 13.5% after 100 cycles of circulation, and the batteries are superior to those of the comparative examples 1, 2 and 3, so that the batteries with the internal spiral graphene frame structure prepared by the invention have obvious influence on the space volume change of the whole negative electrode material, and the silicon volume expansion space can be greatly increased by growing and depositing the graphene on the flexible substrate copper mesh and adding silicon powder to form a spiral structure, and the cycle performance of the lithium battery is ensured.
In the comparative example 1, the graphene nanosheet and the silicon powder are directly subjected to ultrasonic stirring and mixing in the PVP dispersing agent and the CMC thickening agent, vacuum drying and thermosetting treatment are carried out, then silicon dioxide coating treatment is carried out, and due to the lack of the step of dispersing and depositing the copper mesh by the graphene, the obtained mixed slurry has more graphene aggregation and poor dispersion; meanwhile, the dispersibility between the graphene and the silicon powder is poor, so that the battery has low initial capacitance, the capacitance loss is large after 100 cycles, the powder density is high, and the stability of the battery is poor.
In comparative example 2, the flexible substrate loaded with graphene is not subjected to spiral twisting treatment, so that the silicon powder expansion space is small, the silicon powder volume expansion is large, and the first capacitance and the cycle stability of the graphene/silicon composite cathode are affected.
In the comparative example 3, no surface silica gel coating is performed, and no surface protection effect is performed on the silicon/graphene composite negative electrode, so that the nano silicon is in direct contact with the electrolyte, and the cycle performance and the stability of the lithium battery are reduced.
In conclusion, the spiral graphene framework is arranged in the negative electrode material prepared by the invention, so that a larger expansion space is provided for the volume change of silicon in the charging and discharging processes, the structural stability of the negative electrode material is ensured, and the cycle performance of the negative electrode material is improved. Meanwhile, the silicon dioxide coating on the surface can effectively isolate the direct contact between the nano silicon and the electrolyte, thereby improving the cycle performance of the lithium battery. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.

Claims (9)

1. A preparation method of a spiral silicon/graphene composite negative electrode for a lithium battery is characterized by comprising the following steps:
mixing hydroxypropyl methyl cellulose, copper nanowires, propylene glycol, a surfactant and a defoaming agent in deionized water to prepare slurry, flattening the substrate by using a flexible film containing a nickel-chromium alloy coating as a substrate, fixing the flattened substrate on a screen printing machine, printing the slurry on the surface of the flexible substrate according to a pattern, and drying in vacuum to obtain the flexible substrate loaded with the copper nanowires;
fixing the flexible substrate obtained in the step one in a vacuum deposition chamber, and depositing graphene under the catalysis of the copper nanowires by using methane and hydrogen as gas sources to obtain a flexible substrate on which a graphene strip is deposited;
step three, adding nano silicon powder into deionized water, adding a small amount of dispersant and thickener for ultrasonic treatment to obtain nano silicon dispersed slurry, and coating the slurry on the surface of the flexible substrate with the graphene belt obtained in the step two;
step four, subjecting the flexible substrate obtained in the step three to vacuum drying and thermosetting, twisting the flexible substrate according to a spiral structure, fixing the twisted substrate, corroding the flexible substrate by using a ferric trichloride corrosive liquid, unfolding the flexible substrate after the corrosion is finished, adding a deionized water solution for ultrasonic dispersion, taking out the flexible substrate, and filtering and drying to obtain the spiral graphene loaded with the nano silicon particles;
and step five, adding the helical graphene loaded with the nano-silicon particles obtained in the step four into an ethyl orthosilicate aqueous solution, adjusting the pH to acidity for hydrolysis, performing silica gel coating, and finally performing heat treatment in a vacuum furnace to obtain the composite cathode material of the helical graphene/silicon nano-particles coated with silica.
2. The method for preparing a spiral silicon/graphene composite anode for a lithium battery according to claim 1, wherein: in the first step, the flexible substrate is high-temperature-resistant inorganic flexible substrate glass fiber woven cloth.
3. The method for preparing a spiral silicon/graphene composite anode for a lithium battery according to claim 1, wherein: the weight parts of the raw materials in the step one are as follows: 1-4 parts of hydroxypropyl methyl cellulose, 0.5-4 parts of copper nanowires, 1-3 parts of propylene glycol, 1-3 parts of a surfactant, 1-3 parts of a defoaming agent and 15-20 parts of deionized water.
4. The method for preparing a spiral silicon/graphene composite anode for a lithium battery according to claim 1, wherein: the thickness of the deposited graphene in the second step is 100-500 nm; the deposition temperature is 900-1100 ℃.
5. The method for preparing a spiral silicon/graphene composite anode for a lithium battery according to claim 1, wherein: in the third step, the dispersing agent is PVP30, the thickening agent is sodium carboxymethyl cellulose, and the addition mass ratio of PVP30 to sodium carboxymethyl cellulose is 0.5-2: 5-10;
the solid content of the nano silicon dispersion slurry is 15-25%;
the slurry is coated by one of spraying, blade coating and roller coating, and the coating thickness is 10-20 um.
6. The method for preparing a spiral silicon/graphene composite anode for a lithium battery according to claim 1, wherein: the thermal curing treatment in the fourth step is normal pressure muffle furnace thermal treatment curing, and the thermal treatment temperature is 300-350 ℃.
7. The method for preparing a spiral silicon/graphene composite anode for a lithium battery according to claim 1, wherein: the formula of the ferric trichloride corrosive liquid in the fourth step comprises the following components in parts by weight: 500-600 parts of ferric trichloride, 20-100 parts of hydrochloric acid and 1000 parts of water;
the corrosion temperature of the ferric trichloride corrosion solution is 40-60 ℃.
8. The method for preparing a spiral silicon/graphene composite anode for a lithium battery according to claim 1, wherein: in the fifth step, the pH value of the hydrolysis of the tetraethoxysilane is 3-5;
the vacuum heat treatment temperature is 400-600 ℃, and the treatment atmosphere is hydrogen or argon.
9. A spiral silicon/graphene composite negative electrode for a lithium battery, which is characterized in that the silicon/graphene composite negative electrode of the spiral frame is prepared by the preparation method of any one of claims 1 to 8.
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Publication number Priority date Publication date Assignee Title
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115928279A (en) * 2022-12-31 2023-04-07 武汉纺织大学 Graphene/silicone rubber coaxial fiber-based elastic core-spun yarn and preparation and application thereof

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