CN111668463B - Lithium ion battery cathode material and preparation method thereof - Google Patents
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Abstract
The invention relates to a lithium ion battery cathode material and a preparation method thereof, and the lithium ion battery cathode material comprises a pyrolytic carbon-carbon fiber complex with a 5-12 micron core-shell structure, a silicon-silicon carbide composite nanowire with a 400-600 nm diameter, a silicon powder with a 100-300 nm diameter and a carbon microsphere with a 20-60 nm diameter; the pyrolytic carbon-carbon fiber complex, the silicon-silicon carbide composite nanowire, the silicon powder and the carbon microsphere form a three-dimensional tree structure through mixing. The lithium ion battery cathode material is formed into a three-dimensional tree structure by mixing 5-12 microns of pyrolytic carbon-carbon fiber complex with a core-shell structure, 400-600 nm of silicon-silicon carbide composite nanowires, 100-300 nm of silicon powder and 20-60 nm of carbon microspheres, so that the combination degree of all components can be improved, and the specific capacity and the stability of the lithium ion battery cathode material can be further improved.
Description
Technical Field
The invention relates to the technical field of energy storage batteries, in particular to a lithium ion battery cathode material and a preparation method thereof.
Background
Lithium ion batteries have been widely used in smart phones, notebook computers, electric vehicles, and other fields. The lithium ion battery mainly comprises an anode, a cathode, an electrolyte and a diaphragm, wherein the traditional cathode material is graphite, the theoretical specific capacity of the graphite is only 372mAh/g, and the ever-increasing high-energy density requirement of a power battery cannot be completely met. Therefore, the development of a novel high-capacity lithium ion battery cathode material has important practical significance.
In related documents, document 1, "a silicon-based negative electrode material, a preparation method and applications thereof" discloses a silicon-based lithium ion battery negative electrode material composed of porous nano-silicon particles and polymers dispersed in pores; document 2 zhou R, guo h, N-doped carbon layer derived from a polymeric substrate to an extruded the electrochemical performance of a spray-dried Si/graphite composite material for lithium batteries, journal of Alloys and composites, 2016,689: 130-137 "", discloses a core-shell structure anode material in which silicon graphite composite particles are coated with a nitrogen-doped carbon shell; the document 3 Chen Y, hu Y, shen Z, et al, hollow core-shell structured silicon @ carbon nanoparticles embedded in carbon nanoparticles as binder-free anodes for lithium-ion batteries, journal of Power Source, 2017,342: 467-475 "discloses the preparation of Hollow silicon carbon nanocomposite negative electrode materials by etching SiO2 with hydrofluoric acid; document 4"li S, qin X, zhang H, et al, silicon/carbon composite microspheres with a hierarchical core-shell structure as an anode for lithium ion batteries, electrochemical Communications, 2014, 49: 98-102" discloses a negative electrode material of a multi-layer microsphere structure mainly composed of a porous carbon skeleton and nano-Silicon particles and encapsulated in a carbon shell. As can be seen from the negative electrode materials disclosed in documents 1 to 4, the negative electrode materials in the related art have a drawback of low specific capacity and stability.
Disclosure of Invention
The invention aims to provide an improved lithium ion battery cathode material, and further provides a preparation method of the lithium ion battery cathode material.
The technical scheme adopted by the invention for solving the technical problem is as follows: constructing a lithium ion battery cathode material, which comprises a pyrolytic carbon-carbon fiber complex with a 5-12 micron core-shell structure, a silicon-silicon carbide composite nanowire with a 400-600 nanometer structure, silicon powder with a 100-300 nanometer structure and a carbon microsphere with a 20-60 nanometer structure;
the pyrolytic carbon-carbon fiber composite, the silicon-silicon carbide composite nanowire, the silicon powder and the carbon microsphere form a three-dimensional tree structure through mixing.
Preferably, the pyrolytic carbon-carbon fiber composite forms a trunk in the three-dimensional tree-like structure; the silicon-silicon carbide composite nanowire forms a branch in the three-dimensional tree structure; the silicon powder and the carbon microspheres are filled in gaps formed between the pyrolytic carbon-carbon fiber composite and the silicon-silicon carbide composite nanowires;
the mass percentage of the pyrolytic carbon-carbon fiber composite is 60-75%;
the mass percentage of the silicon-silicon carbide composite nanowire is 15-25%;
the mass percentage of the carbon microspheres is 15-25%;
the balance being the mass percent of the silicon powder.
The invention also discloses a preparation method of the lithium ion battery cathode material, which comprises the following steps:
s1, preparing a pyrolytic carbon-carbon fiber complex which is 5-12 microns and has a core-shell structure: introducing inert gas and carbon source gas into carbon fibers, and treating the carbon fibers and the carbon source gas at a high temperature to obtain a pyrolytic carbon-carbon fiber complex with a core-shell structure and a diameter of 5-12 microns;
s2, preparing a first mixture formed by a pyrolytic carbon-carbon fiber complex with a 5-12 micron core-shell structure and a silicon-silicon carbide composite nanowire with a 400-600 nm size: preparing a liquid precursor containing the silicon-silicon carbide composite nanowire, soaking the pyrolytic carbon-carbon fiber composite prepared in the step S1 in the liquid precursor, and standing, air-drying and performing high-temperature treatment to obtain a first mixture;
s3, preparing 20-60 nm carbon microspheres: placing the phenolic aldehyde microspheres in vacuum for high-temperature treatment to obtain carbon microspheres;
s4, preparing a second mixture formed by the first mixture and carbon microspheres with the diameters of 20-60 nanometers: mixing the first mixture and the carbon microspheres according to a second set proportion to obtain a second mixture;
and S5, mixing the second mixture and 100-300 nm silicon powder according to a third set proportion to obtain the lithium ion battery negative electrode material.
Preferably, in the step S1, the temperature under the high temperature condition is 800 to 1000 ℃.
Preferably, in the step S1, the carbon source gas is methane;
the inert gas is argon.
Preferably, in the step S1, the flow rate of the carbon source gas is 0.2 to 0.5L/min;
the flow rate of the inert gas is 0.5 to 1.0L/min.
Preferably, the step S2 includes the steps of:
s2.1, preparing the liquid precursor: mixing tetraethoxysilane and absolute ethyl alcohol according to a first set proportion, uniformly stirring, then adding hydrochloric acid, and continuously stirring to obtain the liquid precursor;
s2.2, soaking the pyrolytic carbon-carbon fiber composite prepared in the step S1 in the liquid precursor, standing for a set time in a normal-temperature environment, air-drying to obtain the pyrolytic carbon-carbon fiber composite doped with the liquid precursor, and then placing in an inert gas environment for high-temperature treatment to obtain the first mixture.
Preferably, in the step S2.1, a first set ratio of the ethyl orthosilicate to the absolute ethyl alcohol is a molar ratio, and the first set ratio is 1;
in the step S2.1, the mass ratio of the hydrochloric acid to the tetraethoxysilane is 1 to 10 to 1;
in the step S2.2, the temperature of the high-temperature treatment is 1000 to 1200 ℃.
Preferably, in the step S3, the temperature for placing the phenolic microspheres under vacuum for high-temperature processing is 700 to 900 ℃.
Preferably, in the step S4, a second set ratio of the first mixture to the carbon microspheres is a mass ratio, and the second set ratio is 1;
in the step S5, a third set ratio of the second mixture to the silicon powder is a mass ratio, and the third set ratio is from 10 to 1.
The lithium ion battery cathode material and the preparation method thereof have the following beneficial effects: the lithium ion battery cathode material is formed into a three-dimensional tree structure by mixing a pyrolytic carbon-carbon fiber complex with a core-shell structure of 5-12 microns, a silicon-silicon carbide composite nanowire with a size of 400-600 nanometers, silicon powder with a size of 100-300 nanometers and carbon microspheres with a size of 20-60 nanometers, so that the combination degree of all components can be improved, and the specific capacity and the stability of the lithium ion battery cathode material can be further improved.
Drawings
The invention will be further described with reference to the accompanying drawings and examples, in which:
FIG. 1 is a schematic structural diagram of a lithium ion battery anode material according to the present invention;
FIG. 2 is an SEM image of the negative electrode material of the lithium ion battery of the invention;
fig. 3 is a flow chart of a method for preparing the lithium ion battery anode material of the invention.
Detailed Description
For a more clear understanding of the technical features, objects and effects of the present invention, embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
Fig. 1 and 2 show a negative electrode material for a lithium ion battery according to the present invention. The lithium ion battery negative electrode material can be coated on a current collector to form a negative electrode sheet. The lithium ion battery negative electrode material has good combination degree of all components, and has higher specific capacity and stability.
As shown in fig. 1 and fig. 2, the lithium ion battery negative electrode material may include a pyrolytic carbon-carbon fiber composite 1, a silicon-silicon carbide composite nanowire 2, a silicon powder 4, and a carbon microsphere 3, and the pyrolytic carbon-carbon fiber composite 1, the silicon-silicon carbide composite nanowire 2, the silicon powder 4, and the carbon microsphere 3 are mixed and coupled between molecules to form a three-dimensional tree structure. By forming the three-dimensional tree-shaped structure, the combination degree of all the components can be improved, and the specific capacity and the stability of the lithium ion battery cathode material can be further improved.
The pyrolytic carbon-carbon fiber composite 1 may have a size of 5 to 12 micrometers, and may have a core-shell structure, and in some embodiments, the pyrolytic carbon-carbon fiber composite 1 may have a hollow tubular shape. Specifically, the pyrolytic carbon-carbon fiber composite 1 may have a diameter of 5 to 12 μm. In some embodiments, the mass percentage of the pyrolytic carbon-carbon fiber composite body 1 may be 60 to 75%. Alternatively, in some embodiments, the pyrolytic carbon-carbon fiber composite 1 is 68% by mass. By using 5 to 12 microns, the formation of the backbone of the pyrolytic carbon-carbon fiber composite 1 is facilitated. In some embodiments, the pyrolytic carbon-carbon fiber composite 1 may optionally have a diameter of 8.5 microns.
The silicon-silicon carbide composite nanowire 2 can be 400-600 nanometers in size, can be linear, and has the mass percentage of 15-25%. Specifically, in some embodiments, the silicon-silicon carbide composite nanowire 2 may have a diameter of 500 nanometers. Alternatively, in some embodiments, the silicon-silicon carbide composite nanowires 2 are 15% by weight. By adopting the silicon-silicon carbide composite nanowire 2 with the size of 400-600 nanometers, branches in a three-dimensional tree structure can be formed. By compounding the 5-12 micron pyrolytic carbon-carbon fiber complex 1 and the 400-600 nanometer silicon-silicon carbide composite nanowire 2, a three-dimensional tree-shaped skeleton can be formed by depending on the specific structure of each component, and the specific capacity and the stability of the lithium ion battery can be further improved.
The carbon microspheres 3 may have a size of 20 to 60 nm, specifically, a diameter of 40 nm in some embodiments, and a mass percentage of 15 to 25% in some embodiments, and may be used to fill the gap between the pyrolytic carbon-carbon fiber composite 1 and the silicon-silicon carbide composite nanowire 2, optionally, the mass percentage of 15% in some embodiments. The carbon microsphere 3 has higher specific surface, stability and thermal stability, so that the stability of the lithium ion battery can be improved.
The size of the silicon powder 4 may be 100-300 nm, the silicon powder 4 is elemental silicon powder, and in some embodiments, the diameter of the silicon powder 4 may be 200 nm. The silicon powder 4 may be present in an amount of 2% by mass, which is the balance, and may be used to fill the gap between the pyrolytic carbon-carbon fiber composite 1 and the silicon-silicon carbide composite nanowire 2.
Fig. 3 shows some preferred embodiments of a method for preparing a negative electrode material of a lithium ion battery according to the present invention. The preparation method of the lithium ion battery cathode material can be used for preparing the lithium ion battery cathode material.
As shown in fig. 3, the preparation method of the lithium ion battery negative electrode material comprises the following steps:
s1, preparing a pyrolytic carbon-carbon fiber complex which is 5-12 microns and has a core-shell structure: and introducing inert gas and carbon source gas into the carbon fibers, and treating the carbon fibers and the carbon source gas at a high temperature to obtain the pyrolytic carbon-carbon fiber complex with the core-shell structure and the diameter of 5-12 microns.
Wherein the inert gas may be argon gas, and the carbon source gas may be methane; the flow rate of the carbon source gas can be 0.2 to 0.5L/min; the flow rate of the inert gas can be 0.5 to 1.0L/min.
Specifically, in some embodiments, the carbon fiber may be placed in a high temperature furnace at a temperature of 800 to 1000 ℃, methane and argon are introduced, and the carbon fiber is processed for 1 to 3 hours, so as to obtain a pyrolytic carbon-carbon fiber composite with a core-shell structure and a diameter of 5 to 12 micrometers. Wherein the flow rate of the methane is 0.2 to 0.5L/min, and the flow rate of the argon is 0.5 to 1.0L/min.
S2, preparing a first mixture formed by a pyrolytic carbon-carbon fiber complex with a 5-12 micron core-shell structure and a silicon-silicon carbide composite nanowire with a 400-600 nm size: and (2) preparing a liquid precursor containing the silicon-silicon carbide composite nanowire, soaking the pyrolytic carbon-carbon fiber composite prepared in the step (S1) in the liquid precursor, and standing, air-drying and performing high-temperature treatment to obtain a first mixture.
Specifically, in some embodiments, this step S2 comprises the steps of:
s2.1, preparing a liquid precursor: mixing ethyl orthosilicate and absolute ethyl alcohol according to a first set proportion, uniformly stirring, adding hydrochloric acid, and continuously stirring to obtain a liquid precursor; wherein the first set proportion is 1 to 5 to 1. Specifically, mixing tetraethoxysilane and absolute ethyl alcohol according to a molar ratio of 1 to 5 to 1, stirring uniformly, adding hydrochloric acid, and continuing stirring for 1 to 2 hours to obtain a liquid precursor of the silicon-silicon carbide composite nanowire, wherein the ratio of the hydrochloric acid to tetraethoxysilane is 1.
S2.2, soaking the pyrolytic carbon-carbon fiber complex prepared in the step S1 in a liquid precursor, standing for a set time in a normal-temperature environment, air-drying to obtain the pyrolytic carbon-carbon fiber complex doped with the liquid precursor, and placing the pyrolytic carbon-carbon fiber complex in an inert gas environment for high-temperature treatment to obtain a first mixture. Wherein the mass percent of the pyrolytic carbon-carbon fiber composite is 60-75%. The liquid precursor is a liquid precursor of the silicon-silicon carbide composite nanowire, wherein the mass percent of the silicon-silicon carbide composite nanowire is 15-25%. The inert gas is argon. Specifically, soaking the pyrolytic carbon-carbon fiber composite in a liquid precursor for 36 to 48 hours at normal temperature, naturally drying in the air to obtain the pyrolytic carbon-carbon fiber composite doped with the liquid precursor, placing the pyrolytic carbon-carbon fiber composite doped with the liquid precursor in an argon atmosphere, carrying out high-temperature heat treatment for 4 to 6 hours at the temperature of 1000 to 1200 ℃, and naturally cooling to obtain a first mixture, wherein the first mixture is a three-dimensional tree-shaped skeleton structure formed by the pyrolytic carbon-carbon fiber composite with a 5-12 micron core-shell structure and a silicon-silicon carbide composite nanowire with a 400-600 nm size.
S3, preparing 20-60 nanometer carbon microspheres: and (3) placing the phenolic aldehyde microspheres in vacuum for high-temperature treatment to obtain the carbon microspheres. Wherein the temperature of the high-temperature treatment can be 700 to 900 ℃. Specifically, the phenolic aldehyde microspheres are placed in a vacuum furnace, processed for 1 to 3 hours under the condition of 700 to 900 ℃, and then naturally cooled to obtain the carbon microspheres with the diameters of 20 to 60 nanometers.
S4, preparing a second mixture formed by the first mixture and carbon microspheres with the diameters of 20-60 nanometers: and mixing the first mixture and the carbon microspheres according to a second set proportion to obtain a second mixture. In some embodiments, the second set ratio is a mass ratio, the second set ratio is 1. The carbon microspheres may be combined with the pyrolytic carbon-carbon fiber composite and the silicon-silicon carbide composite nanowires to form a second mixture by filling gaps formed between the pyrolytic carbon-carbon fiber composite and the silicon-silicon carbide composite nanowires.
And S5, mixing the second mixture and 100-300 nm silicon powder according to a third set proportion to obtain the lithium ion battery negative electrode material. In some embodiments, the third set ratio may be a mass ratio, and the third set ratio may be 10.
The details are described below with reference to specific examples.
Example 1
(1) Placing the carbon fibers in a high-temperature furnace, and treating for 1 hour under the conditions that the temperature is 800 ℃, the methane flow is 0.2L/min and the argon flow is 0.5L/min to obtain a sample A; sample a is a 5-12 micron pyrolytic carbon-carbon fiber composite with a core-shell structure.
(2) Mixing tetraethoxysilane and absolute ethyl alcohol according to a molar ratio of 1; b is a liquid precursor containing the silicon-silicon carbide composite nanowire.
Soaking the sample A in the liquid B for 36 hours at normal temperature, and naturally drying in the air to obtain a sample labeled C; wherein C is a pyrolytic carbon-carbon fiber composite doped with a liquid precursor.
Placing the sample C in an argon atmosphere, carrying out high-temperature heat treatment for 4 hours at the temperature of 1000 ℃, and then naturally cooling to obtain a sample D; wherein D is a first mixture formed by 5-12 micron pyrolytic carbon-carbon fiber composite and 400-600 nanometer silicon-silicon carbide composite nano wires.
(3) Placing the phenolic aldehyde microspheres in a vacuum furnace, treating for 1 hour at 700 ℃, and naturally cooling to obtain a sample E; wherein, the sample E is the carbon microsphere with the diameter of 20-60 nanometers.
(4) Uniformly mixing the sample D and the sample E according to a mass ratio of 1; wherein the sample F is a second mixture formed by 5-12 microns of pyrolytic carbon-carbon fiber composite, 400-600 nm of silicon-silicon carbide composite nano wires and 20-60 nm of carbon microspheres.
(5) And (3) uniformly mixing the sample F with 100-300 nm silicon powder according to the mass ratio of 10.
Example 2
(1) Placing the carbon fibers in a high-temperature furnace, and treating for 3 hours under the conditions that the temperature is 1000 ℃, the methane flow is 0.5L/min and the argon flow is 1.0L/min to obtain a sample A; sample a is a 5-12 micron pyrolytic carbon-carbon fiber composite with a core-shell structure.
(2) Mixing tetraethoxysilane and absolute ethyl alcohol according to a molar ratio of 1; b is a liquid precursor containing the silicon-silicon carbide composite nanowire.
Soaking the sample A into the liquid B for 48 hours at normal temperature, and naturally drying in the air to obtain a sample marked as C; wherein C is a pyrolytic carbon-carbon fiber composite doped with a liquid precursor.
Placing the sample C in an argon atmosphere, carrying out high-temperature heat treatment for 6 hours at 1200 ℃, and then naturally cooling to obtain a sample D; wherein D is a first mixture formed by 5-12 micron pyrolytic carbon-carbon fiber composite and 400-600 nanometer silicon-silicon carbide composite nanowires.
(3) Placing the phenolic aldehyde microspheres in a vacuum furnace, treating for 3 hours at 900 ℃, and naturally cooling to obtain a sample E; wherein, the sample E is a carbon microsphere with the diameter of 20-60 nanometers.
(4) Uniformly mixing the sample D and the sample E according to a mass ratio of 5; wherein the sample F is a second mixture formed by 5-12 microns of pyrolytic carbon-carbon fiber composite, 400-600 nm of silicon-silicon carbide composite nano wires and 20-60 nm of carbon microspheres.
(5) And (3) uniformly mixing the sample F with 100-300 nm silicon powder according to the mass ratio of 20.
Example 3
(1) Placing the carbon fibers in a high-temperature furnace, and treating for 3 hours under the conditions that the temperature is 800 ℃, the methane flow is 0.5L/min and the argon flow is 0.5L/min to obtain a sample A; sample a is a 5-12 micron pyrolytic carbon-carbon fiber composite with a core-shell structure.
(2) Mixing tetraethoxysilane and absolute ethyl alcohol according to a molar ratio of 1; b is a liquid precursor containing the silicon-silicon carbide composite nanowire.
Soaking the sample A into the liquid B for 48 hours at normal temperature, and naturally drying in the air to obtain a sample labeled C; wherein C is a pyrolytic carbon-carbon fiber composite doped with a liquid precursor.
Placing the sample C in an argon atmosphere, performing high-temperature heat treatment for 6 hours at 1000 ℃, and then naturally cooling to obtain a sample D; wherein D is a first mixture formed by 5-12 micron pyrolytic carbon-carbon fiber composite and 400-600 nanometer silicon-silicon carbide composite nano wires.
(3) Placing the phenolic aldehyde microspheres in a vacuum furnace, treating for 1 hour at 900 ℃, and naturally cooling to obtain a sample E; wherein, the sample E is a carbon microsphere with the diameter of 20-60 nanometers.
(4) Uniformly mixing the sample D and the sample E according to a mass ratio of 1; wherein the sample F is a second mixture formed by 5-12 micron pyrolytic carbon-carbon fiber composite, 400-600 nm silicon-silicon carbide composite nano wires and 20-60 nm carbon microspheres.
(5) And uniformly mixing the sample F with 100-300 nm silicon powder according to the mass ratio of 20.
Example 4
(1) Placing the carbon fibers in a high-temperature furnace, and treating for 2 hours under the conditions that the temperature is 900 ℃, the methane flow is 0.3L/min and the argon flow is 0.6L/min to obtain a sample A; sample a is a 5-12 micron pyrolytic carbon-carbon fiber composite with a core-shell structure.
(2) Mixing tetraethoxysilane and absolute ethyl alcohol according to a molar ratio of 1; b is a liquid precursor containing the silicon-silicon carbide composite nanowire.
Soaking the sample A into the liquid B for 42 hours at normal temperature, and naturally drying in the air to obtain a sample labeled C; wherein C is a pyrolytic carbon-carbon fiber composite doped with a liquid precursor.
Placing the sample C in an argon atmosphere, carrying out high-temperature heat treatment for 5 hours at 1100 ℃, and then naturally cooling to obtain a sample D; wherein D is a first mixture formed by 5-12 micron pyrolytic carbon-carbon fiber composite and 400-600 nanometer silicon-silicon carbide composite nanowires.
(3) Placing the phenolic aldehyde microspheres in a vacuum furnace, treating for 2 hours at 800 ℃, and naturally cooling to obtain a sample E; wherein, the sample E is the carbon microsphere with the diameter of 20-60 nanometers.
(4) Uniformly mixing the sample D and the sample E according to a mass ratio of 3; wherein the sample F is a second mixture formed by 5-12 micron pyrolytic carbon-carbon fiber composite, 400-600 nm silicon-silicon carbide composite nano wires and 20-60 nm carbon microspheres.
(5) And uniformly mixing the sample F with 100-300 nm silicon powder according to the mass ratio of 15.
Example 5
(1) Placing the carbon fibers in a high-temperature furnace, and treating for 2 hours under the conditions that the temperature is 800 ℃, the methane flow is 0.3L/min and the argon flow is 1.0L/min to obtain a sample A; sample a is a 5-12 micron pyrolytic carbon-carbon fiber composite with a core-shell structure.
(2) Mixing tetraethoxysilane and absolute ethyl alcohol according to a molar ratio of 1; b is a liquid precursor containing the silicon-silicon carbide composite nanowire.
Soaking the sample A into the liquid B for 40 hours at normal temperature, and naturally drying in the air to obtain a sample marked as C; wherein C is a pyrolytic carbon-carbon fiber composite doped with a liquid precursor.
Placing the sample C in an argon atmosphere, carrying out high-temperature heat treatment for 5 hours at 1100 ℃, and then naturally cooling to obtain a sample D; wherein D is a first mixture formed by 5-12 micron pyrolytic carbon-carbon fiber composite and 400-600 nanometer silicon-silicon carbide composite nano wires.
(3) Placing the phenolic aldehyde microspheres in a vacuum furnace, treating for 3 hours at 900 ℃, and naturally cooling to obtain a sample E; wherein, the sample E is a carbon microsphere with the diameter of 20-60 nanometers.
(4) Uniformly mixing the sample D and the sample E according to a mass ratio of 4; wherein the sample F is a second mixture formed by 5-12 micron pyrolytic carbon-carbon fiber composite, 400-600 nm silicon-silicon carbide composite nano wires and 20-60 nm carbon microspheres.
(5) And uniformly mixing the sample F with 100-300 nm silicon powder according to the mass ratio of 18.
Example 6
(1) Placing the carbon fibers in a high-temperature furnace, and treating for 3 hours under the conditions that the temperature is 1000 ℃, the methane flow is 0.4L/min and the argon flow is 0.8L/min to obtain a sample A; sample a is a 5-12 micron pyrolytic carbon-carbon fiber composite with a core-shell structure.
(2) Mixing tetraethoxysilane and absolute ethyl alcohol according to a molar ratio of 1; b is a liquid precursor containing the silicon-silicon carbide composite nanowire.
Soaking the sample A in the liquid B for 36 hours at normal temperature, and naturally drying in the air to obtain a sample labeled C; wherein C is a pyrolytic carbon-carbon fiber composite doped with a liquid precursor.
Placing the sample C in an argon atmosphere, carrying out high-temperature heat treatment for 5 hours at 1050 ℃, and then naturally cooling to obtain a sample D; wherein D is a first mixture formed by 5-12 micron pyrolytic carbon-carbon fiber composite and 400-600 nanometer silicon-silicon carbide composite nano wires.
(3) Placing the phenolic aldehyde microspheres in a vacuum furnace, treating for 1 hour at 750 ℃, and naturally cooling to obtain a sample E; wherein, the sample E is a carbon microsphere with the diameter of 20-60 nanometers.
(4) Uniformly mixing the sample D and the sample E according to a mass ratio of 2; wherein the sample F is a second mixture formed by 5-12 micron pyrolytic carbon-carbon fiber composite, 400-600 nm silicon-silicon carbide composite nano wires and 20-60 nm carbon microspheres.
(5) And uniformly mixing the sample F with 100-300 nm silicon powder according to the mass ratio of 10.
Example 7
(1) Placing the carbon fibers in a high-temperature furnace, and treating for 2 hours under the conditions that the temperature is 950 ℃, the methane flow is 0.2L/min and the argon flow is 1.0L/min to obtain a sample A; sample a is a 5-12 micron pyrolytic carbon-carbon fiber composite with a core-shell structure.
(2) Mixing tetraethoxysilane and absolute ethyl alcohol according to a molar ratio of 1; b is a liquid precursor containing the silicon-silicon carbide composite nanowire.
Soaking the sample A into the liquid B for 40 hours at normal temperature, and naturally drying in the air to obtain a sample marked as C; wherein C is a pyrolytic carbon-carbon fiber composite doped with a liquid precursor.
Placing the sample C in an argon atmosphere, carrying out high-temperature heat treatment for 5 hours at 1150 ℃, and then naturally cooling to obtain a sample D; wherein D is a first mixture formed by 5-12 micron pyrolytic carbon-carbon fiber composite and 400-600 nanometer silicon-silicon carbide composite nanowires.
(3) Placing the phenolic aldehyde microspheres in a vacuum furnace, treating for 3 hours at 850 ℃, and naturally cooling to obtain a sample E; wherein, the sample E is a carbon microsphere with the diameter of 20-60 nanometers.
(4) Uniformly mixing the sample D and the sample E according to a mass ratio of 4; wherein the sample F is a second mixture formed by 5-12 micron pyrolytic carbon-carbon fiber composite, 400-600 nm silicon-silicon carbide composite nano wires and 20-60 nm carbon microspheres.
(5) And uniformly mixing the sample F with 100-300 nm silicon powder according to the mass ratio of 10.
It is to be understood that the foregoing examples, while indicating the preferred embodiments of the invention, are given by way of illustration and description, and are not to be construed as limiting the scope of the invention; it should be noted that, for those skilled in the art, the above technical features can be freely combined, and several changes and modifications can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention; therefore, all equivalent changes and modifications made within the scope of the claims of the present invention should be covered by the claims of the present invention.
Claims (9)
1. The lithium ion battery cathode material is characterized by comprising a pyrolytic carbon-carbon fiber complex with the diameter of 5-12 microns and a core-shell structure, a silicon-silicon carbide composite nanowire with the diameter of 400-600 nanometers, silicon powder with the diameter of 100-300 nanometers and carbon microspheres with the diameter of 20-60 nanometers;
the pyrolytic carbon-carbon fiber complex, the silicon-silicon carbide composite nanowire, the silicon powder and the carbon microsphere form a three-dimensional tree structure through mixing; wherein the pyrolytic carbon-carbon fiber composite forms a trunk in the three-dimensional tree structure; the silicon-silicon carbide composite nanowire forms a branch in the three-dimensional tree structure; the silicon powder and the carbon microspheres are filled in gaps formed between the pyrolytic carbon-carbon fiber composite and the silicon-silicon carbide composite nanowires;
the mass percentage of the pyrolytic carbon-carbon fiber composite is 60-75%;
the mass percent of the silicon-silicon carbide composite nanowire is 15-25%;
the mass percentage of the carbon microspheres is 15-25%;
the balance being the mass percentage of the silicon powder.
2. The preparation method of the lithium ion battery negative electrode material is characterized by comprising the following steps of:
s1, preparing a pyrolytic carbon-carbon fiber complex which is 5-12 microns in diameter and has a core-shell structure: introducing inert gas and carbon source gas into carbon fibers, and treating the carbon fibers and the carbon source gas at a high temperature to obtain a pyrolytic carbon-carbon fiber complex with the diameter of 5-12 microns and a core-shell structure;
s2, preparing a first mixture formed by a pyrolytic carbon-carbon fiber complex with a diameter of 5-12 microns and a core-shell structure and a silicon-silicon carbide composite nanowire with a diameter of 400-600 nanometers: preparing a liquid precursor containing the silicon-silicon carbide composite nanowire, soaking the pyrolytic carbon-carbon fiber composite prepared in the step S1 in the liquid precursor, and standing, air-drying and performing high-temperature treatment to obtain a first mixture;
s3, preparing carbon microspheres with the diameter of 20-60 nanometers: placing the phenolic aldehyde microspheres in vacuum for high-temperature treatment to obtain carbon microspheres;
s4, preparing a second mixture formed by the first mixture and carbon microspheres with the diameter of 20-60 nanometers: mixing the first mixture and the carbon microspheres according to a second set proportion to obtain a second mixture; the second set proportion of the first mixture to the carbon microspheres is a mass ratio, and the second set proportion is as follows, wherein the mass ratio is 1;
and S5, mixing the second mixture and silicon powder with the diameter of 100-300 nanometers according to a third set proportion to obtain the negative electrode material of the lithium ion battery in claim 1.
3. The method for preparing the negative electrode material of the lithium ion battery according to claim 2, wherein the temperature under the high-temperature condition in the step S1 is 800 to 1000 ℃.
4. The method for preparing the negative electrode material of the lithium ion battery according to claim 2, wherein in the step S1, the carbon source gas is methane;
the inert gas is argon.
5. The preparation method of the negative electrode material of the lithium ion battery according to claim 2, wherein in the step S1, the flow rate of the carbon source gas is 0.2 to 0.5L/min;
the flow rate of the inert gas is 0.5 to 1.0L/min.
6. The preparation method of the lithium ion battery anode material according to claim 2, wherein the step S2 comprises the steps of:
s2.1, preparing the liquid precursor: mixing tetraethoxysilane and absolute ethyl alcohol according to a first set proportion, uniformly stirring, adding hydrochloric acid, and continuously stirring to obtain the liquid precursor;
s2.2, soaking the pyrolytic carbon-carbon fiber composite prepared in the step S1 in the liquid precursor, standing for a set time in a normal-temperature environment, air-drying to obtain the pyrolytic carbon-carbon fiber composite doped with the liquid precursor, and then placing in an inert gas environment for high-temperature treatment to obtain the first mixture.
7. The method for preparing the negative electrode material of the lithium ion battery according to claim 6, wherein in the step S2.1, a first set ratio of the tetraethoxysilane to the absolute ethyl alcohol is a molar ratio, and the first set ratio is 1;
in the step S2.1, the mass ratio of the hydrochloric acid to the tetraethoxysilane is 1;
in the step S2.2, the temperature of the high-temperature treatment is 1000 to 1200 ℃.
8. The preparation method of the negative electrode material for the lithium ion battery according to claim 2, wherein in the step S3, the temperature for placing the phenolic microspheres in vacuum for high-temperature treatment is 700 to 900 ℃.
9. The method for preparing the negative electrode material of the lithium ion battery according to claim 2,
in the step S5, a third set ratio of the second mixture to the silicon powder is a mass ratio, and the third set ratio is from 10 to 1.
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