CN111952577B - C/Si/CNTs composite carbon nanofiber membrane, preparation method and application thereof - Google Patents

C/Si/CNTs composite carbon nanofiber membrane, preparation method and application thereof Download PDF

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CN111952577B
CN111952577B CN202010864591.2A CN202010864591A CN111952577B CN 111952577 B CN111952577 B CN 111952577B CN 202010864591 A CN202010864591 A CN 202010864591A CN 111952577 B CN111952577 B CN 111952577B
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nanofiber membrane
cnts
pan
carbon nanofiber
composite carbon
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CN111952577A (en
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胡毅
张亚茹
程钟灵
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Zhejiang Sci Tech University ZSTU
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention relates to a composite carbon nanofiber membrane, in particular to a C/Si/CNTs composite carbon nanofiber membrane, a preparation method and application thereof, and belongs to the technical field of energy storage system materials. Firstly, preparing a PAN/Si/Fe composite nanofiber membrane by adopting an electrostatic spinning method, growing Carbon Nanotubes (CNTs) on Fe active sites by adopting a Chemical Vapor Deposition (CVD) method on the basis, and then preparing the C/Si/CNTs composite carbon nanofiber membrane by high-temperature carbonization. The energy storage performance of the lithium ion battery is researched by means of an energy storage device of the lithium ion battery. The CNTs grown on the PAN group can effectively relieve the volume expansion of a silicon cathode, and the C/Si/CNTs composite carbon nanofiber membrane provided by the invention is used as the lithium ion battery cathode, so that the capacity attenuation of the lithium ion battery is obviously reduced, and the cycle stability of the battery is improved.

Description

C/Si/CNTs composite carbon nanofiber membrane, preparation method and application thereof
Technical Field
The invention relates to a composite carbon nanofiber membrane, in particular to a C/Si/CNTs composite carbon nanofiber membrane, a preparation method and application thereof, and belongs to the technical field of energy storage system materials.
Background
In recent years, the shortage of energy and the continuous utilization of new renewable energy have become hot spots in social research. The problem of energy storage in the continuous utilization of new energy sources makes energy storage materials a new research hotspot. On one hand, the lithium ion battery is widely applied to the aspects of electric vehicles, portable energy storage equipment and the like as a safe and low-cost electrochemical energy storage device. Silicon (Si) is due to its high theoretical capacity (4200 mAhg)-1) The low working potential and the abundance in nature are expected to become the high-capacity negative electrode of the lithium ion battery. However, its enormous volume expansion during lithiation and delithiation (300%) results in severe electrode structure pulverization and rapid capacity fading, preventing its further practical application.
On the other hand, the research direction of the functional finishing field of the traditional dyeing and finishing industry needs to be expanded urgently, so that the fiber is endowed with the energy storage function, which is a good chance for the traditional dyeing and finishing functional finishing field to change and innovate, and the electrostatic spinning of the silicon/carbon composite nanofiber becomes a breakthrough for the research of the energy storage fiber. But when the lithium ion battery cathode is used as a lithium ion battery cathode, the electrochemical energy storage performance is still not ideal. Because the semiconductor nano Si particles have poor dispersibility, a phenomenon that partial Si particles and aggregates thereof are exposed obviously exists in the silicon/carbon composite nanofiber; these Si particles and their aggregates that are exposed on the fiber surface are more likely to peel off from the fiber surface, resulting in loss of electrical contact, deactivation of the active material, and rapid capacity fade.
Disclosure of Invention
The invention provides a carbon (C)/silicon (Si)/Carbon Nano Tube (CNTs) composite carbon nano fiber membrane, which is used as a lithium ion battery cathode, effectively reduces the capacity attenuation of the lithium ion battery and improves the cycle stability of the battery.
The invention also provides a preparation method of the carbon (C)/silicon (Si)/Carbon Nano Tube (CNTs) composite carbon nanofiber membrane for the lithium ion battery cathode.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a preparation method of a C/Si/CNTs composite carbon nanofiber membrane is characterized by comprising the following steps:
(1) preparing a PAN/Si/Fe composite nanofiber membrane by electrostatic spinning:
mixing Polyacrylonitrile (PAN) powder, silicon powder (Si) and iron salt particles, dissolving the mixture in Dimethylformamide (DMF), and fully stirring the mixture at 40-80 ℃ to obtain uniformly dispersed spinning solution with 5-15% of PAN solid content; in the spinning solution, the mass of PAN is 100%, the Si content is 10% -40%, the ferric salt content is 10-30%, and the PAN/Si/Fe composite nanofiber membrane is obtained after electrostatic spinning is carried out on the spinning solution;
(2) growing Carbon Nanotubes (CNTs) by Chemical Vapor Deposition (CVD):
drying the PAN/Si/Fe composite nanofiber membrane, then placing the dried PAN/Si/Fe composite nanofiber membrane in a tubular furnace, pre-oxidizing the membrane under the air condition, and continuously introducing acetylene under the protection of inert gas to perform a Chemical Vapor Deposition (CVD) Carbon Nanotube (CNTs) process;
(3) preparing a C/Si/CNTs composite carbon nanofiber membrane by high-temperature carbonization:
after the CVD is finished, the temperature is raised to 600-900 ℃ at the speed of 5-10 ℃/min, and the temperature is kept for 4-12h for high-temperature carbonization, so that the C/Si/CNTs composite carbon nanofiber membrane is obtained.
The invention provides an idea for protecting Si nano-particles exposed on the surface of a fiber, and solves the problem of huge volume expansion (-300%) of silicon serving as a lithium ion battery cathode in lithiation and delithiation processes. Firstly, preparing a PAN/Si/Fe composite nanofiber membrane by adopting an electrostatic spinning method, growing Carbon Nanotubes (CNTs) on Fe active sites by adopting a Chemical Vapor Deposition (CVD) method on the basis, and then preparing the C/Si/CNTs composite carbon nanofiber membrane by high-temperature carbonization. The energy storage performance of the lithium ion battery is researched by means of the energy storage device of the lithium ion battery. The CNTs grown on the PAN group can effectively relieve the volume expansion of a silicon cathode, and the C/Si/CNTs composite carbon nanofiber membrane provided by the invention is used as the lithium ion battery cathode, so that the capacity attenuation of the lithium ion battery is obviously reduced, and the cycle stability of the battery is improved.
Preferably, the iron salt in step (1) is one or more selected from ferrous sulfate, ferric chloride, ferroferric oxide and ferrocene. The iron salt functions to provide active sites for the growth of Carbon Nanotubes (CNTs) during Chemical Vapor Deposition (CVD).
In the experimental exploration, the doped ferrous sulfate can better provide more active sites for the growth of the CNTs under the condition of not influencing the flexibility of the carbon nano fibers; the flexibility of the fiber is reduced due to the existence of chloride ions in the ferric chloride, so that the ferric chloride is not beneficial to being used as a slice of a lithium ion battery cathode and battery preparation; under the discussion conditions, CNTs (carbon nanotubes) grown after CVD (chemical vapor deposition) and high-temperature carbonization are fewer, and the improvement of the electrochemical performance when the nano fiber is used as a lithium ion battery cathode is not facilitated.
Preferably, the iron salt is ferrous sulfate, and the content of the ferrous sulfate in the spinning solution ranges from 15% to 20% by taking the mass of the PAN as 100%.
Preferably, the spinning solution contains 8 to 10% of PAN and 15 to 20% of Si, based on 100% of PAN by mass.
Preferably, the PAN/Si/Fe composite nanofiber membrane in the step (2) is dried at the temperature of 60-80 ℃ for 6-24 h.
Preferably, in the step (2), the pre-oxidation temperature is 180-.
Preferably, in the high-temperature carbonization in the step (3), a pure argon (Ar) atmosphere is used to prevent the composite carbon nanofiber film from being oxidized.
Preferably, the distance between the needle head and the aluminum foil receiver is set to be 10-20cm in the electrostatic spinning process in the step (1); during the spinning process, the spinning solution is continuously stirred in order to prevent the Si particles from being unevenly dispersed in the obtained nanofibers.
The invention relates to a C/Si/CNTs composite carbon nanofiber membrane prepared by the method.
The application of the C/Si/CNTs composite carbon nanofiber membrane in the preparation of lithium ion batteries is characterized in that: the C/Si/CNTs composite carbon nanofiber membrane is used as a lithium ion battery cathode.
Preferably, the application is specifically: and cutting the obtained C/Si/CNTs composite carbon nanofiber membrane into round sheets, taking a pure lithium sheet as a positive electrode and the C/Si/CNTs composite carbon nanofiber membrane as a negative electrode, and adding an electrolyte and a diaphragm to assemble the 2032 type button lithium ion half-cell.
It is further preferred that the electrolyte is a 1 mol/L lithium hexafluorophosphate + volume ratio of 1: 1: ethylene Carbonate (EC) of 1: dimethyl carbonate (DMC): ethyl Methyl Carbonate (EMC) (1M LiPF)6+ EC/DMC/EMC (1: 1: 1), the diaphragm is Celgard 2300 polypropylene film.
Compared with the prior art, the invention has the advantages that:
1. the invention adopts a Chemical Vapor Deposition (CVD) method to grow Carbon Nanotubes (CNTs) on the Fe active sites of the silicon-carbon composite nanofibers for the first time, and protects the exposed Si nanoparticles on the surfaces of the nanofibers, thereby being capable of adapting to the volume change of the Si nanoparticles in the charge/discharge process.
2. The C/Si/CNTs composite carbon nanofiber membrane is used as a battery cathode material for a lithium ion battery, and the energy storage performance of the battery cathode material is researched, so that the novel composite material can obviously reduce the capacity attenuation of the lithium ion battery and improve the cycle stability of the battery.
Drawings
FIG. 1 is 15% ferrous sulfate (FeSO)4) SEM images of the composite carbon nanofiber after spinning, CVD and carbonization;
FIG. 2 is an SEM image of a C/Si composite carbon nanofiber without a CVD step;
FIG. 3 is 10% ferrous sulfate (FeSO)4) SEM images of the composite carbon nanofiber after spinning, CVD and carbonization;
FIG. 4 is 20% ferrous sulfate (FeSO)4) SEM images of the composite carbon nanofiber after spinning, CVD and carbonization;
FIG. 5 is an SEM image of composite carbon nanofibers after 15% ferrocene spinning, CVD, and carbonization;
FIG. 6 is 15% ferric chloride (FeCl)2) SEM image of the composite carbon nanofiber after spinning, CVD and carbonization;
FIG. 7 is 15% ferrous sulfate (FeSO)4) TEM images of CNTs after spinning, CVD and carbonization;
FIG. 8 is an EIS diagram of composite carbon nanofibers after spinning, CVD and carbonization of 3 spinning dope formulations;
fig. 9 is a long cycle test plot of a composite carbon nanofiber membrane as an electrode of a lithium ion battery after 15% ferrous sulfate (FeSO 4) spinning, CVD, and carbonization.
Detailed Description
The technical solution of the present invention will be further specifically described below by way of specific examples. It is to be understood that the practice of the invention is not limited to the following examples, and that any variations and/or modifications may be made thereto without departing from the scope of the invention.
In the invention, all parts and percentages are weight units, and all equipment, raw materials and the like can be purchased from the market or are commonly used in the industry, if not specified.
In the following examples, acetylene and argon mixed gas (C) was used in step (2)2H2: ar = 7.95 v%: 92.05 v%) was CVD grown.
Example 1
A preparation method of a carbon (C)/silicon (Si)/Carbon Nano Tube (CNTs) composite carbon nanofiber membrane comprises the following specific steps:
(1) preparing a PAN/Si/CNTs composite nanofiber membrane by electrostatic spinning:
preparing a spinning solution: polyacrylonitrile (PAN) powder, silicon powder (Si) and ferrous sulfate particles are mixed, dissolved in Dimethylformamide (DMF), and stirred at 80 ℃ for 12 hours to obtain a uniformly dispersed spinning solution with 8% PAN solid content. In the spinning solution, the content of Si is 25% and the content of ferrous sulfate is 15% based on the mass of PAN (100%).
Electrostatic spinning: and (3) placing the obtained spinning solution and a magnetic stirring rotor in a needle cylinder together, setting the distance between a needle head and an aluminum foil receiver to be 15cm, setting the spinning voltage to be 15kV, and continuously spinning for 6 hours to obtain the 1.2 mu m PAN/Si/Fe composite nanofiber membrane.
(2) Growing Carbon Nanotubes (CNTs) by Chemical Vapor Deposition (CVD):
taking off the PAN/Si/Fe composite nanofiber membrane obtained by electrostatic spinning, drying at 80 ℃ for 12h, placing in a tubular furnace, pre-oxidizing at 280 ℃ in air atmosphere for 2h, and continuously introducing acetylene and argon mixed gas (C)2H2: ar = 7.95 v%: 92.05 v%) for 30min, and performing a Chemical Vapor Deposition (CVD) Carbon Nanotube (CNTs) process.
(3) Preparing a carbon (C)/silicon (Si)/Carbon Nanotube (CNTs) composite carbon nanofiber membrane by high-temperature carbonization:
and after the CVD is finished, changing the gas atmosphere into pure argon (Ar), heating to 800 ℃ at the speed of 5 ℃/min, and preserving the heat for 4h to finally obtain the C/Si/CNTs composite carbon nanofiber membrane.
The shape scanning electron microscope picture of the C/Si/CNTs composite carbon nanofiber membrane prepared by the method is shown in figure 1, Fe is used as an active site, carbon nanotubes uniformly grow on the surface of the composite nanofiber membrane to form a jungle shape, the volume expansion of Si particles in the fiber and on the surface can be effectively relieved in the lithiation/delithiation process, and the carbon nanotubes are used as an electrode material of a lithium ion battery, so that the improvement of the cycle stability of the lithium ion battery is facilitated. The transmission electron microscope image of the grown CNTs is shown in FIG. 7, the left image is a typical morphology structure of the CNTs, and the obvious lattice structure of the right image shows that the graphitization degree is higher.
Comparative example 1
A preparation method of a C/Si/CNTs composite carbon nanofiber membrane comprises the following specific steps:
(1) preparing a PAN/Si composite nanofiber membrane by electrostatic spinning:
preparing a spinning solution: mixing 8% Polyacrylonitrile (PAN) powder (accounting for the total amount of the spinning solution) and 25% silicon powder (Si) (accounting for PAN), dissolving in Dimethylformamide (DMF), and stirring at 80 deg.C for 12h to obtain a uniformly dispersed spinning solution with a solid content of 8%.
Electrostatic spinning: and (3) placing the obtained spinning solution and a magnetic stirring rotor in a needle cylinder together, setting the distance between a needle head and an aluminum foil receiver to be 15cm, setting the spinning voltage to be 15kV, and continuously spinning for 6 hours to obtain the 1-micron composite PAN/Si nanofiber membrane.
(3) Preparing a carbon (C)/silicon (Si) composite carbon nanofiber membrane by high-temperature carbonization:
the gas atmosphere is pure argon (Ar), pre-oxidation is carried out for 2h at 280 ℃, the temperature is raised to 800 ℃ at 5 ℃/min, and heat preservation is carried out for 4h, thus finally obtaining the C/Si composite carbon nanofiber membrane.
The scanning electron microscope image of the fiber morphology obtained without direct carbonization by CVD is shown in FIG. 2, Si nanoparticles are exposed on the surface of the fiber and agglomerated into large particles which are very unevenly distributed, and if the Si nanoparticles are used as an electrode material of a lithium ion battery, huge volume expansion is generated in the lithiation/delithiation process, so that the electrochemical performance is extremely poor.
Comparative example 2
A preparation method of a C/Si/CNTs composite carbon nanofiber membrane comprises the following specific steps:
(1) preparing a PAN/Si/CNTs composite nanofiber membrane by electrostatic spinning:
preparing a spinning solution: mixing 8% Polyacrylonitrile (PAN) powder (in the total amount of spinning solution), 25% silicon powder (Si) (in PAN), and 10% ferrous sulfate (FeSO)4) The (PAN) particles were mixed, dissolved in Dimethylformamide (DMF) and stirred at 80 ℃ for 12h to obtain a uniformly dispersed dope with a solid content of 8%.
Electrostatic spinning: the same as in example 1.
(2) Growing Carbon Nanotubes (CNTs) by Chemical Vapor Deposition (CVD):
taking off the PAN/Si/Fe composite nanofiber membrane obtained by electrostatic spinning, drying at 80 ℃ for 12h, and placing in a tubeIn a furnace, firstly preoxidizing for 2h at 280 ℃ in air atmosphere, and then continuously introducing acetylene and argon mixed gas (C)2H2: ar = 7.95 v%: 92.05 v%) for 30min, and performing a Chemical Vapor Deposition (CVD) Carbon Nanotube (CNTs) process.
(3) Preparing a carbon (C)/silicon (Si)/Carbon Nanotube (CNTs) composite carbon nanofiber membrane by high-temperature carbonization:
and after the CVD is finished, changing the gas atmosphere into pure argon (Ar), heating to 800 ℃ at the speed of 5 ℃/min, and preserving the heat for 4h to finally obtain the C/Si/CNTs composite carbon nanofiber membrane.
Adding 10% ferrous sulfate (FeSO)4) As shown in a scanning electron microscope image of the fiber after spinning, CVD and carbonization, although partial CNTs grow, the number of the grown CNTs is limited due to few active sites of Fe, the effect of relieving the volume expansion of Si is not enough, and the CNTs cannot play the role of improving the electrochemical performance when being used as an electrode material of a lithium ion battery.
Comparative example 3
A preparation method of a C/Si/CNTs composite carbon nanofiber membrane comprises the following specific steps:
(1) preparing a PAN/Si/CNTs composite nanofiber membrane by electrostatic spinning:
preparing a spinning solution: mixing 8% Polyacrylonitrile (PAN) powder (in the total amount of spinning solution), 25% silicon powder (Si) (in PAN), and 20% ferrous sulfate (FeSO)4) The (PAN) particles were mixed, dissolved in Dimethylformamide (DMF) and stirred at 80 ℃ for 12h to obtain a uniformly dispersed dope with a solid content of 8%.
Electrostatic spinning: the same as in example 1.
(2) Growing Carbon Nanotubes (CNTs) by Chemical Vapor Deposition (CVD): the same as in example 1.
(3) Preparing a carbon (C)/silicon (Si)/Carbon Nanotube (CNTs) composite carbon nanofiber membrane by high-temperature carbonization: the same as in example 1.
Adding 20% ferrous sulfate (FeSO)4) Scanning electron micrographs of fibers after spinning, CVD and carbonization are shown in FIG. 4, which shows that CNTs are grown to tightly coat the nanofibers, but the activity is increased due to the increased Fe contentThe increase of the sites and the excessive growth of the CNTs lead the nanofiber membrane to become brittle, so that the nanofiber membrane can not be completely sliced into the electrode plate of the lithium ion battery.
Comparative example 4
A preparation method of a C/Si/CNTs composite carbon nanofiber membrane comprises the following specific steps:
(1) preparing a PAN/Si/CNTs composite nanofiber membrane by electrostatic spinning:
preparing a spinning solution: mixing 8% Polyacrylonitrile (PAN) powder (accounting for the total amount of the spinning solution), 25% silicon powder (Si) (accounting for PAN) and 15% ferrocene (accounting for PAN) particles, dissolving in Dimethylformamide (DMF), and stirring at 80 ℃ for 12h to obtain the uniformly dispersed spinning solution with the solid content of 8%.
Electrostatic spinning: the same as in example 1.
(2) Growing Carbon Nanotubes (CNTs) by Chemical Vapor Deposition (CVD): the same as in example 1.
(3) Preparing a carbon (C)/silicon (Si)/Carbon Nanotube (CNTs) composite carbon nanofiber membrane by high-temperature carbonization: the same as in example 1.
The shape scanning electron microscope image of the composite nanofiber added with 15% of ferrocene is shown in fig. 5, and it is found that Si is still exposed on the surface of the fiber and is seriously agglomerated, and although there is an Fe active site, there is almost no CNTs growth, which is not favorable for improving the electrochemical performance of the composite nanofiber in the application of a lithium ion battery.
Comparative example 5
A preparation method of a C/Si/CNTs composite carbon nanofiber membrane comprises the following specific steps:
(1) preparing a PAN/Si/CNTs composite nanofiber membrane by electrostatic spinning:
preparing a spinning solution: mixing 8% Polyacrylonitrile (PAN) powder (in the total amount of spinning solution), 25% silicon powder (Si) (in PAN), and 15% ferric chloride (FeCl)2) The (PAN) particles were mixed, dissolved in Dimethylformamide (DMF) and stirred at 80 ℃ for 12h to obtain a uniformly dispersed dope with a solid content of 8%.
Electrostatic spinning: the same as in example 1.
(2) Growing Carbon Nanotubes (CNTs) by Chemical Vapor Deposition (CVD): the same as in example 1.
(3) Preparing a carbon (C)/silicon (Si)/Carbon Nanotube (CNTs) composite carbon nanofiber membrane by high-temperature carbonization: the same as in example 1.
15% iron chloride (FeCl)2) The scanning electron microscope image of the morphology of the composite nanofiber is shown in fig. 6, many CNTs grow on the surface of the nanofiber, but a fiber film is very fragile and is not beneficial to slicing.
Application example 1
The C/Si/CNTs composite carbon nanofiber membrane prepared by the invention is mainly applied to the preparation of lithium ion batteries and is used as a battery cathode.
Cutting the C/Si/CNTs composite carbon nanofiber membrane obtained in example 1 into disks with the diameter of 12mm, adding 1 mol/L lithium hexafluorophosphate to serve as a lithium ion battery cathode, wherein the volume ratio of the lithium hexafluorophosphate to the carbon nanofiber membrane is 1: 1: ethylene Carbonate (EC) of 1: dimethyl carbonate (DMC): ethyl Methyl Carbonate (EMC) (1M LiPF)6 A2032 type button lithium ion half-cell is assembled by + EC/DMC/EMC (1: 1: 1) as electrolyte and Celgard 2300 polypropylene film as separator, and the electrochemical performance is characterized, and the result is shown in figure 9.
Adding 10% ferrous sulfate (FeSO)4) 15% ferrous sulfate (FeSO)4) And 20% ferrous sulfate (FeSO)4) The composite carbon nanofiber membrane is prepared into a lithium ion battery electrode for electrochemical performance test after being prepared into spinning solution and subjected to spinning, CVD and carbonization. FIG. 8 is a graph comparing EIS of FeSO4The increase of the amount reduces the impedance of the battery, but the flexibility of the battery is poor in view of the surface appearance of the battery, and electrode slicing is not facilitated, so that the spinning solution added with 15% of ferrous sulfate is selected as the optimal spinning solution formula.
The long cycle test chart of the lithium ion battery prepared by using the composite carbon nanofiber membrane prepared by adding 15% ferrous sulfate spinning solution through spinning, CVD and high-temperature carbonization as an electrode is shown in FIG. 9, and the long cycle test chart is shown in FIG. 2-1At the current density, after circulating for 50 circles, 750mAhg is still kept-1The specific discharge capacity and the coulombic efficiency are kept above 98 percent. Shows that CNTs grown on PAN base can effectively relieve severe volume expansion of silicon in lithiation/delithiation processThe capacity attenuation of the lithium ion battery can be obviously reduced, and the cycling stability of the battery is improved. Other iron salts and the proportion have relatively weak effects, but still play a certain role in relieving the volume of silicon.
The embodiments are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same or similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
The C/Si/CNTs composite carbon nanofiber membrane, the preparation method and the application thereof provided by the invention are described in detail above. The principles and embodiments of the present invention are explained herein using specific examples, which are presented only to assist in understanding the method and its core concepts. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.

Claims (7)

1. A preparation method of a C/Si/CNTs composite carbon nanofiber membrane is characterized by comprising the following steps in sequence:
(1) preparing a PAN/Si/Fe composite nanofiber membrane by electrostatic spinning:
mixing Polyacrylonitrile (PAN) powder, silicon powder (Si) and iron salt particles, dissolving the mixture in Dimethylformamide (DMF), and fully stirring the mixture at 40-80 ℃ to obtain uniformly dispersed spinning solution with 5-15% of PAN solid content; in the spinning solution, the mass of PAN is 100%, the Si content is 10% -40%, the ferric salt content is 10-30%, and the PAN/Si/Fe composite nanofiber membrane is obtained after electrostatic spinning is carried out on the spinning solution;
the ferric salt is ferrous sulfate, and the content of the ferrous sulfate in the spinning solution is 15% by taking the mass of the PAN as 100%; in the spinning solution, the mass of PAN is 100%, the content of PAN is 8% -10%, and the content of Si is 15% -20%;
(2) growing Carbon Nanotubes (CNTs) by Chemical Vapor Deposition (CVD):
drying the PAN/Si/Fe composite nanofiber membrane, then placing the dried PAN/Si/Fe composite nanofiber membrane in a tubular furnace, pre-oxidizing the membrane under the air condition, and continuously introducing acetylene under the protection of inert gas to perform a Chemical Vapor Deposition (CVD) Carbon Nanotube (CNTs) process;
(3) preparing a C/Si/CNTs composite carbon nanofiber membrane by high-temperature carbonization:
after the Chemical Vapor Deposition (CVD) is finished, the temperature is raised to 600-900 ℃ at the speed of 5-10 ℃/min, and the temperature is kept for 4-12h for high-temperature carbonization, so that the C/Si/CNTs composite carbon nanofiber membrane is obtained.
2. The method of claim 1, wherein: and (3) drying the PAN/Si/Fe composite nanofiber membrane in the step (2) at the temperature of 60-80 ℃ for 6-24 h.
3. The method of claim 1, wherein: in the step (2), the pre-oxidation temperature is 180-300 ℃, and the pre-oxidation time is 0.5-3 h.
4. The method of claim 1, wherein: and (4) adopting pure argon (Ar) atmosphere in the high-temperature carbonization process in the step (3).
5. A C/Si/CNTs composite carbon nanofiber membrane made by the method of claim 1.
6. An application of the C/Si/CNTs composite carbon nanofiber membrane of claim 1 in the preparation of lithium ion batteries is characterized in that: the C/Si/CNTs composite carbon nanofiber membrane is used as a lithium ion battery cathode.
7. Use according to claim 6, characterized in that: the application specifically comprises the following steps: and cutting the obtained C/Si/CNTs composite carbon nanofiber membrane into round sheets, taking a pure lithium sheet as a positive electrode and the C/Si/CNTs composite carbon nanofiber membrane as a negative electrode, and adding an electrolyte and a diaphragm to assemble the 2032 type button lithium ion half-cell.
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