CN115602802A - Porous silicon-carbon composite negative electrode material, preparation method and application thereof, and lithium ion battery - Google Patents

Porous silicon-carbon composite negative electrode material, preparation method and application thereof, and lithium ion battery Download PDF

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CN115602802A
CN115602802A CN202110771305.2A CN202110771305A CN115602802A CN 115602802 A CN115602802 A CN 115602802A CN 202110771305 A CN202110771305 A CN 202110771305A CN 115602802 A CN115602802 A CN 115602802A
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silicon
negative electrode
nano
carbon composite
carbon
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徐军红
陈和平
陈玉
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LUOYANG YUEXING NEW ENERGY TECHNOLOGY CO LTD
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LUOYANG YUEXING NEW ENERGY TECHNOLOGY CO LTD
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    • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
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    • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
    • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
    • D04H1/70—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres
    • D04H1/72—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres the fibres being randomly arranged
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    • Y02E60/10—Energy storage using batteries

Abstract

The invention belongs to the field of preparation of lithium ion battery materials, and particularly discloses a porous silicon-carbon composite negative electrode material, a preparation method and application thereof, and a lithium ion battery. According to the invention, a polymer and tetraethoxysilane are combined by an electrostatic spinning method to form a nanofiber membrane with high strength and proper pores, so that a proper space is provided for embedding of nano silicon and carbon nanotubes later, the volume expansion of silicon in the charging and discharging process is greatly relieved, and the cycle performance is improved; according to the invention, nano silicon and carbon nanotubes are filled in the interlamination and pore structures of the nanofiber membrane, so that the tap density and the contact area of the material are improved, and the electronic impedance is reduced; the invention also utilizes the coupling effect of the silane coupling agent among the nano silicon, the carbon nano tube and the nano fiber membrane to improve the conductivity and the structural stability of the material, and finally obtains the silicon-carbon composite cathode material with high porosity, large specific surface area and low expansion rate. The method has simple preparation process and simple and convenient operation, and is suitable for planning industrial production.

Description

Porous silicon-carbon composite negative electrode material, preparation method and application thereof, and lithium ion battery
Technical Field
The invention belongs to the field of preparation of lithium ion battery materials, and particularly relates to a porous silicon-carbon composite negative electrode material, a preparation method and application thereof, and a lithium ion battery.
Background
With the increase of the demand of marketization on the lithium ion battery with high specific energy density, the lithium ion battery cathode material is required to have high specific capacity and low expansion, and most of the lithium ion battery cathodes in the current market adopt graphite as a raw material, the theoretical capacity of the graphite is only 372mAh/g, and the requirement of the market on higher performance of the cathode material is difficult to meet.
The silicon material is uniformly paid attention by researchers due to the advantages of the silicon material such as the theoretical capacity of up to 4200mAh/g, lower lithium removal potential, rich storage capacity and the like. However, the silicon material has huge volume change and low conductivity during charging and discharging, and the rate capability and the cycle performance of the silicon material are seriously influenced. In the past decades, efforts have been made to improve the electrochemical performance of silicon-based anode materials. For example, to reduce the grain size of silicon to a nanometer level or to have amorphous structural features to relieve structural stress caused by excessive volume change. However, the nano silicon particles have large surface energy and are easily agglomerated to cause capacity fading, which also offsets the advantages of the nano particles. In addition, the problem of poor conductivity cannot be solved by the nano-formation of silicon material. Therefore, it is considered that the silicon material is compounded with other materials by a suitable preparation method to obtain the silicon-based composite material, and the physical properties of the other materials are utilized to improve the electrochemical performance of the simple substance silicon. The method is more ideal for compounding the silicon material with the carbon material with stable structure and excellent conductivity, and the carbon material is used for relieving the volume expansion effect of the silicon and providing a transmission channel of electrons and lithium ions while fully playing the high capacity of the silicon material. However, the actually prepared silicon-carbon composite material has low first efficiency while reducing volume expansion, the electronic conductivity is not obviously improved, and material peeling is easy to occur between the silicon core and the shell carbon in the long-term circulation process, so that the circulation performance of the silicon-carbon composite material is influenced. In order to solve the problem, chinese patent application CN106129367a discloses a silicon/carbon nano composite fiber, which is composed of carbon fiber and silicon nano particles, wherein a hollow structure is formed on the surface of the carbon fiber and embedded with the silicon nano particles, and a gap exists between the silicon nano particles and the carbon fiber to accommodate the volume expansion of the silicon nano particles. The composite material can protect single silicon particles in the carbon fibers, and the structural stability of the composite material is improved due to the existence of the void structure. However, the preparation process of the material is complicated, and the conductivity needs to be further improved.
Disclosure of Invention
The invention aims to provide a porous silicon-carbon composite negative electrode material, which solves the problems of poor conductivity and unstable structure of the existing silicon-carbon material.
Secondly, the invention provides a preparation method of the porous silicon-carbon composite negative electrode material.
The invention further provides application of the porous silicon-carbon composite negative electrode material in preparation of a lithium ion battery.
Finally, the invention provides a lithium ion battery using the porous silicon-carbon composite negative electrode material.
In order to realize the purpose, the technical scheme adopted by the invention is as follows:
a porous silicon-carbon composite negative electrode material is prepared by a method comprising the following steps:
(1) Mixing a polymer, tetraethoxysilane and an organic solvent to obtain a precursor solution;
taking the precursor solution to carry out electrostatic spinning to obtain a nanofiber membrane;
(2) Dispersing the nanofiber membrane in a silane coupling agent solution, uniformly mixing the nanofiber membrane with nano silicon and a conductive agent, then carrying out hydrothermal reaction, cleaning with acid liquor after the reaction, and drying to obtain a silicon oxide compound/nano silicon composite material;
and soaking the silicon oxide compound/nano silicon composite material in an ammonium fluoride solution, taking out the composite material and carbonizing the composite material to obtain the silicon oxide/nano silicon composite material.
According to the invention, the polymer and the tetraethoxysilane are combined through electrostatic spinning, the formed nanofiber membrane has high strength and proper pores, a proper space is provided for the embedding of the nanometer silicon, the expansion of the silicon in the charging and discharging process is greatly relieved, and the cycle performance is improved. Meanwhile, the nano-silicon is filled between the nano-fiber membrane layers, so that the tap density and the contact area of the material are improved, the electronic impedance of the material is reduced, the bonding force between the nano-silicon and a silicon oxide compound (such as silicon dioxide) is improved by utilizing the bridge function of the silane coupling agent between the nano-silicon and the nano-fiber membrane, and the structural stability of the material is improved. According to the invention, the silane coupling agent is added before the hydrothermal reaction, so that the dispersibility of the nano silicon and the carbon nano tube is increased, the binding capacity of the nano silicon and the carbon nano tube with the nanofiber membrane is improved, and a network structure is formed; the silane coupling agent also generates silicon radicals during the hydrothermal reaction, and then the silicon radicals are cooled to generate a material containing a silicon-oxygen compound. That is, the hydrothermal reaction is mainly to generate radicals by vaporization of a material, and then the radicals are combined to generate different compounds when the temperature is lowered.
As a preferred embodiment, in step (1), the polymer is selected from one or more of polyvinyl alcohol, polyvinylidene fluoride, polyethylene oxide, polyvinyl acetate, polyvinyl butyral, and polyvinyl pyrrolidone. Further preferably, the polymer is selected from one of polyvinyl alcohol, polyethylene oxide and polyvinyl acetate.
As a preferred embodiment, in the step (1), the organic solvent is one or more selected from ethanol, ethylene glycol, isopropanol, glycerol, N-dimethylformamide, and N-methylpyrrolidone. Further preferably, the organic solvent is one selected from the group consisting of ethylene glycol, isopropyl alcohol, and N, N-dimethylformamide.
In a preferred embodiment, in the step (1), the mass ratio of the polymer, the tetraethoxysilane and the organic solvent is (1-12): (1-12): 100.
as a preferred embodiment, in step (1), the process parameters of the electrostatic spinning are as follows: the receiving distance is 10-20 cm, the voltage is 10-20 kV, the injection speed of the spinning solution (namely precursor solution) is 0.01-0.1 mL/min, and the rotating speed of the roller receiving device is 50-100 r/min.
In a preferred embodiment, in step (1), the nanofiber membrane is obtained by drying at 40 to 60 ℃ for 40 to 60 hours under vacuum after the electrospinning. Further preferably, the drying is carried out at 50 ℃ under vacuum for 48h.
As a preferred embodiment, in the step (2), the silane coupling agent is selected from one or more of gamma-aminopropyltriethoxysilane (KH-550), gamma- (2,3-glycidoxy) propyltrimethoxysilane (KH-560), and gamma- (methacryloyloxy) propyltrimethoxysilane (KH-570).
As a preferred embodiment, in the step (2), one or more of ethylene glycol, isopropanol, dichloromethane, petroleum ether and toluene are used as a solvent in the preparation of the silane coupling agent solution. The concentration of the silane coupling agent solution is 0.1-0.4 wt%.
As a preferable embodiment, in the step (2), the conductive agent is carbon nanotubes.
In a preferred embodiment, in the step (2), the mass ratio of the nanofiber membrane, the silane coupling agent, the nano-silicon and the carbon nanotubes is (10 to 20): (0.5-2): (1-5): (0.5-2).
In a preferred embodiment, in the step (2), the hydrothermal reaction is carried out at a temperature of (100 to 200 ℃) for a reaction time of (1 to 6) hours. The hydrothermal reaction conditions can ensure that the materials are fully mixed, and the hydrothermal synthesis method has the advantages of good uniformity, high synthesis efficiency and good consistency.
In a preferred embodiment, in step (2), the acid solution is a dilute hydrochloric acid solution, and the concentration is (0.5-2) wt%, and more preferably 1wt%. The washing with the acid solution is performed at least 2 times, preferably 3 times. The main function of the acid cleaning is to remove the slightly alkaline silane coupling agent, and simultaneously, the hydrogen ions in the hydrochloric acid slightly etch the surface of the silicon compound.
As a preferred embodiment, in the step (2), the drying is freeze-drying. Preferably, the freeze drying is carried out for 40-60 h at (-20 to-40) DEG C. More preferably, it is freeze-dried at-30 ℃ for 48h.
In a preferred embodiment, in the step (2), the ammonium fluoride solution is an aqueous solution of ammonium fluoride. The concentration of the ammonium fluoride solution is 40 to 60%, preferably 50%. One of the purposes of soaking in the ammonium fluoride solution is to utilize nitrogen element doping in the ammonium fluoride to improve the electronic conductivity of the material, and on the other hand, the aqueous solution of the ammonium fluoride is an acidic solution which can slightly etch the surface of the silicon-based material.
In a preferred embodiment, in the step (2), the soaking time is (24 to 72) hours.
In a preferred embodiment, in the step (2), the raw material is dried at 70 to 90 ℃ under vacuum for 24 to 48 hours before the carbonization treatment. Preferably, the drying is carried out at 80 ℃ under vacuum.
As a preferred embodiment, in the step (2), the carbonization conditions are as follows: heating to 600-1000 ℃ at a heating rate of 1-10 ℃/min under an inert atmosphere, and keeping the temperature for 1-24 hours.
In a preferred embodiment, in step (2), after the carbonization treatment, the temperature is naturally reduced to room temperature in an inert atmosphere, and then the porous silicon-carbon composite negative electrode material is obtained by ball milling and crushing. The inert atmosphere is argon atmosphere. The particle size of the porous silicon-carbon composite negative electrode material is (1-15) mu m, preferably (5-10) mu m.
A preparation method of a porous silicon-carbon composite negative electrode material comprises the following steps:
(1) Mixing a polymer, tetraethoxysilane and an organic solvent to obtain a precursor solution;
taking the precursor solution to carry out electrostatic spinning to obtain a nanofiber membrane;
(2) Dispersing the nanofiber membrane in a silane coupling agent solution, uniformly mixing the nanofiber membrane with nano silicon and a conductive agent, then carrying out hydrothermal reaction, cleaning with acid liquor after the reaction, and drying to obtain a silicon oxide compound/nano silicon composite material;
and (3) soaking the silicon-oxygen compound/nano-silicon composite material in an ammonium fluoride solution, taking out the silicon-oxygen compound/nano-silicon composite material, and carbonizing the silicon-oxygen compound/nano-silicon composite material to obtain the silicon-oxygen compound/nano-silicon composite material.
As a preferable embodiment, in the step (1), the polymer is selected from one or more of polyvinyl alcohol, polyvinylidene fluoride, polyethylene oxide, polyvinyl acetate, polyvinyl butyral, and polyvinyl pyrrolidone. Further preferably, the polymer is selected from one of polyvinyl alcohol, polyethylene oxide and polyvinyl acetate.
As a preferred embodiment, in the step (1), the organic solvent is one or more selected from ethanol, ethylene glycol, isopropanol, glycerol, N-dimethylformamide, and N-methylpyrrolidone. Further preferably, the organic solvent is one selected from the group consisting of ethylene glycol, isopropyl alcohol, and N, N-dimethylformamide.
In a preferred embodiment, in the step (1), the mass ratio of the polymer, the tetraethoxysilane and the organic solvent is (1-12): (1-12): 100.
as a preferred embodiment, in step (1), the process parameters of the electrostatic spinning are as follows: the receiving distance is 10-20 cm, the voltage is 10-20 kV, the injection speed of the spinning solution (namely precursor solution) is 0.01-0.1 mL/min, and the rotating speed of the roller receiving device is 50-100 r/min.
In a preferred embodiment, in step (1), the nanofiber membrane is obtained by drying at 40 to 60 ℃ for 40 to 60 hours under vacuum after the electrospinning. Further preferably, the drying is carried out at 50 ℃ under vacuum for 48h.
As a preferred embodiment, in the step (2), the silane coupling agent is selected from one or more of gamma-aminopropyltriethoxysilane (KH-550), gamma- (2,3-glycidoxy) propyltrimethoxysilane (KH-560) and gamma- (methacryloyloxy) propyltrimethoxysilane (KH-570).
As a preferred embodiment, in the step (2), one or more of ethylene glycol, isopropanol, dichloromethane, petroleum ether and toluene are used as a solvent in the preparation of the silane coupling agent solution. The concentration of the silane coupling agent solution is 0.1-0.4 wt%.
As a preferable embodiment, in the step (2), the conductive agent is carbon nanotubes.
In a preferred embodiment, in the step (2), the mass ratio of the nanofiber membrane, the silane coupling agent, the nano-silicon and the carbon nanotubes is (10 to 20): (0.5-2): (1-5): (0.5-2).
In a preferred embodiment, in the step (2), the hydrothermal reaction is carried out at a temperature of (100 to 200 ℃) for a reaction time of (1 to 6) hours.
In a preferred embodiment, in step (2), the acid solution is a dilute hydrochloric acid solution, and the concentration is (0.5-2) wt%, and more preferably 1wt%. The washing with acid is carried out at least 2 times, preferably 3 times.
As a preferred embodiment, in the step (2), the drying is freeze-drying. Preferably, the freeze-drying is carried out at (-20 to-40) DEG C for (40 to 60) h. More preferably, it is freeze-dried at-30 ℃ for 48h.
In a preferred embodiment, in the step (2), the ammonium fluoride solution is an aqueous solution of ammonium fluoride. The concentration of the ammonium fluoride solution is 40 to 60%, preferably 50%.
In a preferred embodiment, in the step (2), the soaking time is (24 to 72) hours.
In a preferred embodiment, in the step (2), the raw material is dried at 70 to 90 ℃ under vacuum for 24 to 48 hours before the carbonization treatment. Preferably, the drying is carried out at 80 ℃ under vacuum.
As a preferred embodiment, in the step (2), the carbonization conditions are as follows: heating to 600-1000 ℃ at a heating rate of 1-10 ℃/min under an inert atmosphere, and keeping the temperature for 1-24 hours.
In a preferable embodiment, in the step (2), after the carbonization treatment, the temperature is naturally reduced to room temperature under an inert atmosphere, and then the porous silicon-carbon composite negative electrode material is obtained by ball milling and crushing. The inert atmosphere is argon atmosphere. The particle size of the porous silicon-carbon composite negative electrode material is (1-15) mu m, preferably (5-10) mu m.
According to the invention, the polymer and the tetraethoxysilane are combined through electrostatic spinning, so that the formed nanofiber membrane has the advantages of high strength and moderate pore space, a proper space is provided for the embedding of the nanometer silicon and the carbon nano tube, the volume expansion of the silicon in the charging and discharging process is greatly relieved, and the cycle performance of the silicon is improved. Meanwhile, nano silicon and carbon nanotubes are doped between network layers formed by nano fibers by a hydrothermal method, and the conductivity and the structural stability of the material are improved by utilizing the coupling effect of a silane coupling agent between the nano silicon and the carbon nanotubes and a nanofiber membrane, so that the silicon-carbon composite cathode material with high porosity, large specific surface area and low expansion rate is finally obtained.
An application of a porous silicon-carbon composite negative electrode material in the preparation of a lithium ion battery.
The lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm and electrolyte, wherein the negative electrode comprises a negative electrode current collector and a negative electrode material layer coated on the surface of the negative electrode current collector, the negative electrode material layer comprises a negative electrode material, a conductive agent and a binder, and the negative electrode material adopts the porous silicon-carbon composite negative electrode material.
The invention has the beneficial effects that:
in the porous silicon-carbon composite negative electrode material, nano silicon is uniformly dispersed in meshes of a frame formed by nano fibers, and the fibers are mutually staggered and penetrated to form pores, so that the volume expansion of silicon can be reduced; meanwhile, the invention utilizes the network structure formed by the coupling action of the silane coupling agent among the nano silicon, the carbon nano tube and the nano fiber membrane to improve the conductivity and the structural stability of the material, and finally obtains the silicon-carbon composite cathode material with high porosity, large specific surface area, low expansion rate and high specific capacity.
The preparation method comprises the steps of firstly preparing a polymer/ethyl orthosilicate nanofiber membrane, then soaking the membrane in a dispersion solution of nano silicon and carbon nano tubes, and sequentially carrying out hydrothermal reaction, freeze drying and carbonization treatment to obtain the porous silicon-carbon composite negative electrode material. The method has simple preparation process and simple and convenient operation, is suitable for planning industrial production, and accords with the modern green environmental protection concept.
Drawings
FIG. 1 is an SEM image (10 μm) of a porous Si-C composite anode material in example 1 of the present invention;
FIG. 2 is an SEM image (3 μm) of a porous Si-C composite anode material in example 1 of the present invention.
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings obtained in the experimental examples are briefly described above. It is understood that the above-mentioned drawings only show some experimental examples of the present invention and should not be considered as limiting the scope of protection of the claims in any way. For a person skilled in the art, it is possible to derive other relevant figures from these figures without inventive effort.
Detailed Description
In order to make the technical problems to be solved, the technical solutions adopted and the technical effects achieved by the present invention easier to understand, the technical solutions of the present invention are clearly and completely described below with reference to specific examples, comparative examples and experimental examples. It is to be noted that the examples, comparative examples and experimental examples, in which specific conditions are not specified, were conducted according to conventional conditions or conditions recommended by the manufacturers. The reagents, instruments and the like used in examples, comparative examples and experimental examples were all purchased from commercial sources.
Example 1
The porous silicon-carbon composite negative electrode material is prepared by the method comprising the following steps of:
(1) Preparing a nanofiber membrane:
dissolving 5g of polyvinyl alcohol and 5g of tetraethoxysilane in 100mL of glycol organic solvent to obtain a precursor solution;
carrying out electrostatic spinning on the precursor solution (the receiving distance is 15cm, the voltage is 15kV, the injection speed of the spinning solution is 0.05mL/min, and the rotating speed of a roller receiving device is 80 r/min), and then drying for 48h under the vacuum condition of 50 ℃ to obtain a nanofiber membrane;
(2) Preparing a porous silicon-carbon composite negative electrode material:
dispersing 15g of a nanofiber membrane in 500mL of glycol organic solvent of gamma-aminopropyltriethoxysilane with the concentration of 0.2wt%, then adding 3g of nano-silicon and 1g of carbon nano-tubes, uniformly mixing, transferring to a high-pressure reaction kettle, reacting for 3 hours at the temperature of 150 ℃, then cleaning for 3 times by using 1wt% of dilute hydrochloric acid, and freeze-drying for 48 hours at the temperature of-30 ℃ to obtain a silicon oxide/nano-silicon composite material;
and transferring the silicon oxide compound/nano silicon composite material into an ammonium fluoride solution with the concentration of 50%, soaking for 48h, filtering, vacuum drying (80 ℃,36 h), heating to 700 ℃ at the heating rate of 5 ℃/min under the argon inert atmosphere, preserving heat for 12h, naturally cooling to room temperature under the argon inert atmosphere, ball-milling, and crushing to obtain the porous silicon-carbon composite negative electrode material.
Example 2
The porous silicon-carbon composite negative electrode material is prepared by the method comprising the following steps of:
(1) Preparing a nanofiber membrane:
dissolving 1g of polyoxyethylene and 1g of tetraethoxysilane in 100mL of isopropanol organic solvent to obtain a precursor solution;
carrying out electrostatic spinning on the precursor solution (the receiving distance is 10cm, the voltage is 10kV, the injection speed of the spinning solution is 0.01mL/min, and the rotating speed of a roller receiving device is 50 r/min), and then drying for 48h under the vacuum condition of 50 ℃ to obtain a nanofiber membrane;
(2) Preparing a porous silicon-carbon composite negative electrode material:
dispersing 10g of a nanofiber membrane in 500mL of isopropanol organic solvent of gamma- (methacryloyloxy) propyl trimethoxy silane with the concentration of 0.1wt%, then adding 1g of nano-silicon and 0.5g of carbon nano-tubes, uniformly mixing, transferring to a high-pressure reaction kettle, reacting for 6 hours at the temperature of 100 ℃, then cleaning for 3 times by using 1wt% of dilute hydrochloric acid, and freeze-drying for 48 hours at the temperature of-30 ℃ to obtain a silicon oxide/nano-silicon composite material;
and transferring the silicon oxide compound/nano silicon composite material into an ammonium fluoride solution with the concentration of 50%, soaking for 24h, filtering, vacuum drying (80 ℃,36 h), heating to 600 ℃ at the heating rate of 1 ℃/min under the argon inert atmosphere, preserving heat for 24h, naturally cooling to room temperature under the argon inert atmosphere, ball-milling, and crushing to obtain the porous silicon-carbon composite negative electrode material.
Example 3
The porous silicon-carbon composite negative electrode material is prepared by the method comprising the following steps of:
(1) Preparing a nanofiber membrane:
dissolving 10g of polyvinyl acetate and 10g of tetraethoxysilane in 100mL of N, N-dimethylformamide organic solvent to obtain precursor solution;
carrying out electrostatic spinning on the precursor solution (the receiving distance is 20cm, the voltage is 20kV, the injection speed of the spinning solution is 0.1mL/min, and the rotating speed of a roller receiving device is 100 r/min), and then drying for 48h under the vacuum condition of 50 ℃ to obtain a nanofiber membrane;
(2) Preparing a porous silicon-carbon composite negative electrode material:
dispersing 20g of a nanofiber membrane in 500mL of dichloromethane organic solvent of gamma- (2,3-epoxypropoxy) propyl trimethoxy silane with the concentration of 0.4wt%, then adding 5g of nano silicon and 2g of carbon nano tubes, uniformly mixing, transferring to a high-pressure reaction kettle, reacting for 1h at the temperature of 200 ℃, then cleaning for 3 times by adopting 1wt% of dilute hydrochloric acid, and freeze-drying for 48h at the temperature of-30 ℃ to obtain a silicon oxide/nano silicon composite material;
and transferring the silicon oxide compound/nano silicon composite material into an ammonium fluoride solution with the concentration of 50%, soaking for 72h, filtering, vacuum drying (80 ℃ and 36 h), heating to 1000 ℃ at the heating rate of 10 ℃/min under the argon inert atmosphere, preserving heat for 1h, naturally cooling to room temperature under the argon inert atmosphere, ball-milling, and crushing to obtain the porous silicon-carbon composite negative electrode material.
Comparative example
The silicon-carbon composite negative electrode material of the comparative example is prepared by the method comprising the following steps:
adding 15g of silicon dioxide and 3g of nano silicon into 100mL of ethylene glycol, uniformly mixing by ball milling, transferring into a tube furnace, heating to 700 ℃ at a heating rate of 5 ℃/min under an argon inert atmosphere, keeping the temperature for 12h, naturally cooling to room temperature under the argon inert atmosphere, and carrying out ball milling and crushing to obtain the silicon-carbon composite negative electrode material.
Examples of the experiments
1. SEM test
SEM test was performed on the silicon carbon composite anode material of example 1, and the test results are shown in fig. 1 and 2.
As can be seen from FIG. 1, the particle size of the silicon-carbon composite negative electrode material is 5-10 μm, and the size distribution is uniform and reasonable.
As can be seen from fig. 2, the silicon-carbon composite anode material has a porous structure.
2. Physical and chemical testing
According to the method of the national standard GBT-245332009 graphite cathode material for lithium ion batteries, the silicon-carbon composite cathode materials of examples 1 to 3 and the silicon-carbon composite cathode material of comparative example 1 were subjected to physicochemical tests, and the specific surface area, the powder conductivity and the porosity thereof were respectively tested, and the test results are shown in Table 1.
TABLE 1 results of physical and chemical tests
Sample (I) Specific surface area (m) 2 /g) Conductivity (S/CM) Porosity (%)
Example 1 9.9 9.6 28.5
Example 2 8.8 9.1 26.7
Example 3 7.5 8.3 25.4
Comparative example 1 2.9 1.5 15.5
As can be seen from table 1, the silicon-carbon composite negative electrode material of the present invention has a pore structure between layers of the nanofiber membrane, such that the porosity and the specific surface area are relatively large, and the silica compound and the nano-silicon can be fully mixed uniformly and contact well by using a hydrothermal method, and the silicon-carbon composite negative electrode material contains a carbon nanotube with high conductivity, such that the conductivity is improved.
3. Button cell performance test
The silicon-carbon composite negative electrode materials of examples 1 to 3 and the silicon-carbon composite negative electrode material of comparative example 1 were used as one of the active materials to prepare a pole piece, and the specific preparation method was: adding 9g of active material, 0.5g of conductive agent SP and 0.5g of binder LA136D into 220mL of deionized water, and uniformly stirring to obtain slurry; and coating the slurry on a copper foil current collector to obtain the copper foil current collector.
The pole piece with the silicon-carbon composite negative electrode material of example 1 doped with 80% of artificial graphite as an active material is labeled a, the pole piece with the silicon-carbon composite negative electrode material of example 2 doped with 80% of artificial graphite as an active material is labeled B, the pole piece with the silicon-carbon composite negative electrode material of example 3 doped with 80% of artificial graphite as an active material is labeled C, and the pole piece with the silicon-carbon composite material of comparative example 1 doped with 80% of artificial graphite as an active material is labeled D.
The prepared pole piece is used as a positive electrode, and the positive electrode, a lithium piece, electrolyte and a diaphragm are assembled into a button cell in a glove box with the oxygen and water contents lower than 0.1 ppm. Wherein the diaphragm is celegard 2400; the electrolyte is LiPF 6 Solution, liPF 6 Is 1mol/L, and the solvent is a mixed solution of Ethylene Carbonate (EC) and diethyl carbonate (DMC) (the weight ratio is 1:1). Respectively marking the button cell as A-1,B-1,C-1 and D-1, and then testing the performance of the button cell by adopting a blue light tester under the following test conditions: charging and discharging at 0.1C rate, with voltage range of 0.05-2V, and stopping after 3 weeks of circulation. The test results are shown in table 2.
TABLE 2 button cell Performance test results
Lithium ion battery First discharge capacity (mAh/g) First efficiency (%)
A-1 1568.4 84.9
B-1 1531.6 84.1
C-1 1498.9 84.3
D-1 1139.4 77.1
As can be seen from table 2, the button cell prepared by using the silicon-carbon composite negative electrode material of the present invention has high first discharge capacity and first efficiency, on one hand, the gram capacity performance of the material is improved due to the high electronic conductivity of the silicon-carbon composite negative electrode material; on the other hand, the hydrothermal method can make nano-silicon and silicon oxide fully contact and uniformly mix, and then generate materials such as silicon monoxide and the like in the sintering process (the nano-silicon and silicon dioxide can generate disproportionation reaction at 900 ℃ to generate the silicon monoxide, and the ICP elemental analysis of the materials shows that the composite material contains the silicon oxide compounds such as the silicon monoxide and the like), so that the discharge capacity of the materials is improved.
4. Laminate polymer battery performance test
The prepared pole piece is used as a negative electrode and is mixed with a positive ternary material (LiNi) 1/3 Co 1/3 Mn 1/3 O 2 ) The electrolyte and the diaphragm are assembled into the 5Ah soft package battery. Wherein the diaphragm is celegard 2400, and the electrolyte is LiPF 6 Solution (the solvent is a mixed solution of EC and DEC with the volume ratio of 1:1, liPF 6 The concentration of (1.3 mol/L). And marking the prepared soft package batteries as A-2, B-2, C-2 and D-2 respectively.
The following performance tests were performed on the pouch cells:
(1) Dissecting and testing the thicknesses D1 of the negative pole pieces of the soft package batteries A-2, B-2, C-2 and D-2 with constant volume; then, circulating each soft package battery for 100 times (1C/1C, 25 +/-3 ℃, 2.8-4.2V), fully charging the soft package battery, and dissecting and testing the thickness D2 of the circulated negative pole piece; the swelling ratio was then calculated and the results are shown in table 3. The imbibing ability of each pole piece was also tested, and the results are shown in table 3.
Figure BDA0003153560790000101
TABLE 3 negative pole piece expansion ratio test results
Lithium ion battery D1(μm) D2(μm) Swelling ratio (%) Pole piece imbibition (mL/min)
A-2 105 155 47.6 9.7
B-2 104 154.8 48.8 9.1
C-2 106 156.1 47.3 8.9
E-2 105 182.7 74 2.5
As can be seen from table 3, the expansion rate of the negative electrode plate of the soft-package battery using the silicon-carbon composite negative electrode material of the present invention is significantly lower than that of the comparative example, and the reason for this is as follows: the composite material contains a network structure formed by silicon oxide compounds (mainly silicon dioxide) fibers with high mechanical strength, can buffer volume expansion in the charging and discharging process, and meanwhile, the carbon nano tube has high specific surface area, thereby being beneficial to improving the liquid absorption capacity of the negative pole piece.
(2) Respectively carrying out cycle performance tests on the soft package batteries A-2, B-2, C-2 and D-2 under the following test conditions: the charging and discharging voltage range is 2.8-4.2V, the temperature is 25 +/-3.0 ℃, the charging and discharging multiplying power is 1.0C/1.0C, and the test results are shown in Table 4.
Table 4 soft package battery cycle performance test results
Figure BDA0003153560790000102
As can be seen from table 4, the cycle performance of the pouch battery prepared by using the silicon-carbon composite negative electrode material of the present invention is better than that of the comparative example at each stage of the cycle, and the reason for this is that: the network structure in the composite material reduces the expansion rate and improves the cycle performance.
According to the invention, the polymer and the tetraethoxysilane are combined by an electrostatic spinning method to form the nanofiber membrane with high strength and proper pores, so that a proper space is provided for the embedding of the nanometer silicon and the carbon nano tube, the volume expansion of the silicon in the charging and discharging process is greatly relieved, and the cycle performance is improved; meanwhile, the nano-silicon and the carbon nano-tubes are filled between layers of the nano-fiber film, so that the tap density and the contact area of the material are improved, and the electronic impedance is reduced; the invention also utilizes the coupling effect of the silane coupling agent among the nano silicon, the carbon nano tube and the nano fiber membrane to improve the conductivity and the structural stability of the material, and finally obtains the silicon-carbon composite cathode material with high porosity, large specific surface area and low expansion rate. In the composite material, the nano silicon and the carbon nano tubes are uniformly dispersed in the frame meshes formed by the nano fibers, and the fibers are mutually staggered and penetrated to form pores, so that the volume expansion of silicon can be effectively reduced, and the conductivity and the structural stability of the material are improved.
The method of the invention utilizes the porous technology, on one hand, the multidirectional expansion of silicon in the circulation process can be restrained, the consumption of lithium ions is reduced, meanwhile, the multidimensional structure can expand in more directions, the expansion of the silicon in the vertical plane direction is reduced, and the electronic conductivity of the material is reduced by utilizing the silicon and carbon composite technology. The method comprises the steps of firstly preparing a polymer/ethyl orthosilicate nanofiber membrane, then soaking the membrane in a dispersion solution of nano silicon and carbon nano tubes, and sequentially carrying out hydrothermal reaction, freeze drying and carbonization treatment to obtain the porous silicon-carbon composite negative electrode material. The method has the advantages of simple preparation process and simple and convenient operation, is suitable for planned industrial production, and the obtained composite material has the characteristics of high porosity, large specific surface area, low expansion rate, high specific capacity and the like, so that the prepared lithium ion battery has better rate performance and cycle performance.
The above are only preferred embodiments and experimental examples of the present invention, and do not limit the scope of the present invention. It will be apparent to those skilled in the art that various changes and modifications may be made in the invention as embodied and described. Any modification, replacement (equivalent), improvement and the like made within the spirit of the present invention should be included in the scope of protection of the present invention.

Claims (10)

1. A porous silicon-carbon composite negative electrode material is characterized in that: the composite anode material is prepared by a method comprising the following steps of:
(1) Mixing a polymer, tetraethoxysilane and an organic solvent to obtain a precursor solution;
taking the precursor solution to carry out electrostatic spinning to obtain a nanofiber membrane;
(2) Dispersing the nanofiber membrane in a silane coupling agent solution, uniformly mixing with nano silicon and a conductive agent, then carrying out hydrothermal reaction, cleaning with an acid solution after the reaction, and drying to obtain a silicon-oxygen compound/nano silicon composite material;
and soaking the silicon oxide compound/nano silicon composite material in an ammonium fluoride solution, taking out the composite material and carbonizing the composite material to obtain the silicon oxide/nano silicon composite material.
2. The porous silicon-carbon composite anode material according to claim 1, wherein: in the step (1), the polymer is selected from one or more of polyvinyl alcohol, polyvinylidene fluoride, polyethylene oxide, polyvinyl acetate, polyvinyl butyral and polyvinyl pyrrolidone; and/or the organic solvent is selected from one or more of ethanol, glycol, isopropanol, glycerol, N-dimethylformamide and N-methylpyrrolidone; and/or the mass ratio of the polymer to the tetraethoxysilane to the organic solvent is (1-12): (1-12): 100.
3. the porous silicon-carbon composite anode material according to claim 1, wherein: in the step (2), the silane coupling agent is selected from one or more of gamma-aminopropyltriethoxysilane, gamma- (2,3-glycidoxy) propyl-trimethoxysilane and gamma- (methacryloyloxy) propyl-trimethoxysilane; and/or the conductive agent is a carbon nano tube, and the mass ratio of the nanofiber membrane, the silane coupling agent, the nano silicon and the carbon nano tube is (10-20): (0.5-2): (1-5): (0.5 to 2); and/or the temperature of the hydrothermal reaction is 100-200 ℃, and the reaction time is 1-6 h; and/or the concentration of the ammonium fluoride solution is 40-60%, and the soaking time is 24-72 h; and/or the carbonization treatment conditions are as follows: heating to 600-1000 ℃ at a heating rate of 1-10 ℃/min under an inert atmosphere, and preserving heat for 1-24 h.
4. The porous silicon carbon composite anode material according to any one of claims 1 to 3, wherein: the particle size of the composite negative electrode material is 1-15 μm, preferably 5-10 μm.
5. A preparation method of a porous silicon-carbon composite negative electrode material is characterized by comprising the following steps: the method comprises the following steps:
(1) Mixing a polymer, tetraethoxysilane and an organic solvent to obtain a precursor solution;
taking the precursor solution to carry out electrostatic spinning to obtain a nanofiber membrane;
(2) Dispersing the nanofiber membrane in a silane coupling agent solution, uniformly mixing the nanofiber membrane with nano silicon and a conductive agent, then carrying out hydrothermal reaction, cleaning with acid liquor after the reaction, and drying to obtain a silicon oxide compound/nano silicon composite material;
and soaking the silicon oxide compound/nano silicon composite material in an ammonium fluoride solution, taking out the composite material and carbonizing the composite material to obtain the silicon oxide/nano silicon composite material.
6. The method for preparing the porous silicon-carbon composite anode material according to claim 5, wherein the method comprises the following steps: in the step (1), the polymer is selected from one or more of polyvinyl alcohol, polyvinylidene fluoride, polyethylene oxide, polyvinyl acetate, polyvinyl butyral and polyvinyl pyrrolidone; and/or the organic solvent is selected from one or more of ethanol, glycol, isopropanol, glycerol, N-dimethylformamide and N-methylpyrrolidone; and/or the mass ratio of the polymer to the tetraethoxysilane to the organic solvent is (1-12): (1-12): 100.
7. the method for preparing the porous silicon-carbon composite anode material according to claim 5, wherein the method comprises the following steps: in the step (2), the silane coupling agent is selected from one or more of gamma-aminopropyltriethoxysilane, gamma- (2,3-glycidoxy) propyltrimethoxysilane and gamma- (methacryloyloxy) propyltrimethoxysilane; and/or the conductive agent is a carbon nano tube, and the mass ratio of the nanofiber membrane, the silane coupling agent, the nano silicon and the carbon nano tube is (10-20): (0.5-2): (1-5): (0.5 to 2); and/or the temperature of the hydrothermal reaction is 100-200 ℃, and the reaction time is 1-6 h; and/or the acid solution is a dilute hydrochloric acid solution, and the concentration of the acid solution is 0.5-2 wt%.
8. The method for preparing the porous silicon-carbon composite anode material according to claim 5, wherein the method comprises the following steps: in the step (2), the concentration of the ammonium fluoride solution is 40-60%, and the soaking time is 24-72 h; and/or the carbonization treatment conditions are as follows: heating to 600-1000 ℃ at a heating rate of 1-10 ℃/min under an inert atmosphere, and preserving heat for 1-24 h.
9. The application of the porous silicon-carbon composite negative electrode material as defined in any one of claims 1 to 4 or the porous silicon-carbon composite negative electrode material prepared by the preparation method as defined in any one of claims 5 to 8 in the preparation of lithium ion batteries.
10. A lithium ion battery, characterized by: the lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm and electrolyte, wherein the negative electrode comprises a negative electrode current collector and a negative electrode material layer coated on the surface of the negative electrode current collector, the negative electrode material layer comprises a negative electrode material, a conductive agent and a binder, and the negative electrode material adopts the porous silicon-carbon composite negative electrode material as defined in any one of claims 1 to 4 or the porous silicon-carbon composite negative electrode material prepared by the preparation method as defined in any one of claims 5 to 8.
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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114242987A (en) * 2021-12-22 2022-03-25 格龙新材料科技(常州)有限公司 Preparation method of three-dimensional porous silicon-carbon composite material
CN114242987B (en) * 2021-12-22 2023-09-26 格龙新材料科技(常州)有限公司 Preparation method of three-dimensional porous silicon-carbon composite material

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