CN113594440A - Lithium ion battery cathode material with multilevel conductive structure and preparation method thereof - Google Patents

Lithium ion battery cathode material with multilevel conductive structure and preparation method thereof Download PDF

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CN113594440A
CN113594440A CN202110770281.9A CN202110770281A CN113594440A CN 113594440 A CN113594440 A CN 113594440A CN 202110770281 A CN202110770281 A CN 202110770281A CN 113594440 A CN113594440 A CN 113594440A
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liquid metal
lithium ion
ion battery
micron silicon
anode material
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CN113594440B (en
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吴士超
赵子云
韩俊伟
肖菁
陈凡奇
杨全红
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Tianjin University
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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
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • 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
    • 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
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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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
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Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a lithium ion battery cathode material with a multilevel conductive structure. Compared with the prior art, the invention introduces the liquid metal with fluidity and conductivity, and the liquid metal is crushed along with the deformation of micron silicon, so that the good electrical contact among the crushed particles is maintained by the short-range conductive network; and the carbon nano-fiber constructs a long-range conductive network, so that the electron transport capacity of the micron silicon electrode can be improved. The multi-stage conductive structure from the material to the electrode can improve the stability of the micron silicon electrode and promote the utilization rate of micron silicon active particles, thereby improving the rate capability and the cycle performance of the micron silicon cathode. The invention also provides a method for preparing the material.

Description

Lithium ion battery cathode material with multilevel conductive structure and preparation method thereof
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a lithium ion battery cathode material with a multistage conductive structure and a preparation method thereof.
Background
Lithium ion batteries, which are secondary batteries with a high degree of commercialization at present, have the advantages of high energy density, long cycle life, environmental friendliness, and the like, and are the key points of research and development in recent years. The negative electrode material of the lithium ion battery is the key for determining the energy density and the cycle performance of the battery, however, the traditional graphite negative electrode material has lower theoretical specific capacity (372 mAh g)-1) The improvement of the energy density of the battery is restricted, and the development requirement of the high-performance lithium ion battery cannot be met.
The silicon material has low potential platform, rich reserve and environmental protection, has the specific capacity ten times that of graphite, and is the most potential next generation high energy density lithium ion battery cathode material. However, silicon contributes a large capacity and also seriously swells and breaks in alloying/dealloying with lithium, thereby exposing a new surface, continuously consuming limited electrolyte, forming a Solid Electrolyte Interface (SEI) film, and seriously affecting the electrochemical performance. The use of the nano silicon effectively improves the specific mass capacity and the cycling stability of the silicon, but the production cost is high, and the tap density is low, so that the requirement of the current battery on high volume energy density is difficult to meet; and the specific surface area is large, the first coulombic efficiency is low, and the industrial development process is greatly limited. The micron silicon has low cost, high tap density and small specific surface area, is an ideal material for solving the problems of the nano silicon, but the micron silicon has more serious cracking and pulverization phenomena in the process of lithium intercalation and deintercalation due to larger particle size, so that electric contact among active particles and between the active particles and a current collector is lost, and the original advantages of the micron silicon are difficult to exert. Electrical failures due to silicon volume changes can be buffered to some extent by designing conductive networks such as carbon coatings, however, since such designs are static, electrical connections between active species cannot be effectively maintained for long periods of time during cycling.
In view of the above, the present invention aims to provide a lithium ion battery cathode material with a multilevel conductive structure, which accommodates large volume expansion by designing a micron silicon-liquid metal-carbon coating layer and a carbon nanofiber composite structure, so as to ensure an ion transmission path and good electrical contact, improve cycle stability and rate capability, and further improve volume energy density.
Disclosure of Invention
The invention aims to: aiming at the defects of the prior art, on the basis of the structure of the traditional silicon-carbon composite material, the lithium ion battery cathode material capable of conducting in multiple stages is provided, and the large-volume expansion is accommodated by designing the micron silicon-liquid metal-carbon coating layer and the carbon nanofiber composite structure, so that an ion transmission path and good electrical contact are ensured, the circulation stability and the rate capability are improved, and the volume energy density is further improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
the lithium ion battery anode material with the multilevel conductive structure is characterized by comprising active particles and carbon nanofibers dispersed among the active particles, wherein the active particles comprise a core structure and a shell structure, the core structure comprises micron silicon and liquid metal, and the shell structure is a carbon coating layer.
As an improvement of the lithium ion battery cathode material with the multilevel conductive structure, the liquid metal is gallium-indium alloy or gallium-indium-tin alloy.
As an improvement of the lithium ion battery cathode material with the multilevel conductive structure, the thickness of the shell structure is 10-20 nm; the particle size of the liquid metal is 500 nm-3 mu m, and the particle size of the micron silicon is 3-5 mu m. Experimental studies have shown that liquid metal particles are most suitable for catalyzing the growth of carbon fibers and the in-situ disruption recoating process within this range. The carbon nano-fiber has a length of 5-100 μm and a diameter of about 30-50 nm.
As an improvement of the lithium ion battery cathode material with the multilevel conductive structure, in the cathode material, the total content of the carbon coating layer and the carbon nanofiber is 5-18%, the silicon content is 40-50%, and the liquid metal content is 40-50%.
As an improvement of the lithium ion battery cathode material with the multilevel conductive structure, the density of the cathode material is 4.10-4.20 g cm-3。
Compared with the prior art, the method adopts commercial micron silicon (3-5 microns) as a raw material for constructing the silicon-carbon cathode of the lithium ion battery, utilizes the amorphous, flowable and conductive properties of liquid metal to fill gaps among crushed silicon particles, establishes real-time adaptive electrical contact along with the crushing of the micron silicon, gradually realizes in-situ recoating of the crushed silicon particles, maintains effective electrical contact among the crushed particles, reduces the loss of active substances, maintains electrical integrity and improves the utilization rate of the silicon active substances; meanwhile, the catalytic action of the liquid metal can catalyze the surfaces of the micron silicon particles to generate a three-dimensional carbon nanofiber network, and the dispersed silicon particles are closely connected by utilizing the advantage of long-range conduction. Finally, the liquid metal-micron silicon composite material can simultaneously realize the electronic conduction characteristics of the active particle layer and the electrode layer, and is beneficial to constructing the high-capacity, long-cycle and high-rate micron silicon cathode of the lithium ion battery.
In other words, the invention introduces room temperature liquid metal with fluidity and conductivity, and the metal is crushed along with the deformation of micron silicon, so as to maintain good electrical contact among the crushed particles through a short-range conductive network; and the carbon nanofibers generated by in-situ catalysis construct a long-range conductive network, and the electron transport capacity of the micron silicon electrode is improved. The multi-stage conductive structure from the material to the electrode can improve the stability of the micron silicon electrode and promote the utilization rate of micron silicon active particles, thereby improving the rate capability and the cycle performance of the micron silicon cathode.
The invention also aims to provide a preparation method of the lithium ion battery cathode material with the multilevel conductive structure, which at least comprises the following steps:
firstly, ultrasonically dispersing liquid metal in a solvent, adding micron silicon for continuous ultrasonic treatment to obtain uniform dispersion liquid, and centrifugally separating and drying to obtain a mixture of the micron silicon and the liquid metal;
and secondly, growing a carbon coating layer on the surface of the mixture formed by the micron silicon and the liquid metal by adopting a chemical vapor deposition method to form active particles, and growing carbon nano-fibers between the adjacent active particles to obtain the cathode material.
As an improvement of the preparation method of the lithium ion battery cathode material with the multilevel structure, in the first step, the solvent is isopropanol or ethanol; the ultrasonic power is 200-300W, the ultrasonic time is 0.5-5h, and the ultrasonic power and the ultrasonic time can ensure that the liquid metal is dispersed into particles with the particle size of 500 nm-3 mu m. In order to remove the solvent completely, the drying temperature is 70-90 deg.C, and the drying time is 2-24 h.
As an improvement of the preparation method of the lithium ion battery cathode material with the multilevel structure, in the second step, the chemical vapor deposition method comprises the following specific steps: under the protection of inert gas, the mixture of micron silicon and liquid metal is placed in a corundum crucible, a carbon source is added into a tubular furnace, the temperature is raised to 900-. The formation of carbon layers and carbon fibers can be achieved with a heat treatment temperature of 900-. The carbon source is decomposed at a proper temperature and deposited on the surface of particles of a mixture formed by micron silicon and liquid metal, and the liquid metal has a catalytic effect and can help the carbon fibers grow long and smooth.
As an improvement of the preparation method of the lithium ion battery cathode material with the multilevel structure, the carbon source is at least one of methane and acetylene.
As an improvement of the preparation method of the lithium ion battery cathode material with the multilevel structure, in the second step, the inert gas is argon or argon.
Compared with the prior art, the interface affinity of the liquid metal and the micron silicon is improved through high-temperature treatment, the carbon layer is coated on the surface of a mixture formed by the micron silicon and the liquid metal to form a core-shell structure, and the 3D carbon fiber network generated in situ is connected with each dispersed core-shell particle (active particle), so that the composite material with short-distance conductivity inside the liquid metal and long-distance conductivity outside the carbon fiber is obtained. By controlling the dosage of the liquid metal, the dosage of the liquid metal filling the gaps among the crushed silicon particles is searched, so that the full electrical contact of the surfaces of the crushed silicon particles is met; the diameter, the length and the smoothness of the carbon fiber can be regulated and controlled by setting the size of the liquid metal particles, the gas velocity, the temperature and the like of vapor deposition; the invention improves the electron transmission capability of the material-electrode layer and the electrochemical performance of the electrode material by effectively controlling and coordinating the material, so that the electrode material can be better applied to lithium ion batteries.
The composite material solves the problem of electrical loss after the huge volume expansion and crushing of micron silicon in the material, and ensures the electronic conductivity of the composite material. The material has the advantages of novel structure, good conductivity, large electrochemical lithium storage capacity, good cycling stability and the like, and meanwhile, the preparation method is simple, the cost is low, and the material is suitable for industrialization. When the material is used as a lithium ion battery cathode material, the mass capacity can reach 500-plus-2000 mAh/g, and the volume specific capacity can reach 900-plus-3000 mAh/cm3And has excellent cycle performance and rate capability.
In addition, the method of the invention also has the following advantages:
firstly, the method has mild conditions, simple operation and green and pollution-free preparation process, and the uniform dispersion of the micron silicon, the particle size control of the liquid metal and the uniform mixing of the micron silicon and the liquid metal can be met by utilizing the conventional ultrasonic dispersion technology, so that the problem of poor electrical contact caused by the breakage of the micron silicon in the circulation process is solved.
Secondly, the quality of the carbon product is regulated and controlled by changing parameters of the chemical vapor deposition process, including the addition amount of a carbon source, the deposition temperature, the deposition time and the like, so that the carbon nano fiber with smooth surface and high crystallinity can be grown in situ, and the improvement of the integral conductivity of the electrode is facilitated.
Thirdly, by accurately controlling the proportion and the morphology of the micron silicon, the liquid metal and the carbon material, the conductive connection of the micron silicon in the circulation process and the structural stability and the electrical connection of an electrode can be simultaneously met, the utilization rate of the micron silicon in the circulation process is improved, and the method has very important significance for improving the quality and the volume performance of the lithium ion battery.
Drawings
The invention and its advantageous effects are explained in detail below with reference to the accompanying drawings and the detailed description.
FIG. 1 is a schematic structural diagram of the present invention.
Fig. 2 is a TEM image of the anode material prepared in example 1 of the present invention.
Fig. 3 is a constant current charge and discharge curve of a lithium ion battery made of the negative electrode material prepared in example 1 of the present invention.
Fig. 4 is a rate performance graph of a lithium ion battery made using the negative electrode material prepared in example 1 of the present invention.
Detailed Description
The technical solutions of the present invention are described below with specific examples, but the scope of the present invention is not limited thereto.
Example 1
As shown in fig. 1, the present embodiment provides a lithium ion battery anode material with a multilevel conductive structure, the anode material includes an active particle 1 and a carbon nanofiber 2 dispersed between the active particles 1, the active particle 1 includes a core structure 11 and a shell structure 12, the core structure 11 includes micron silicon and liquid metal, and the shell structure 12 is a carbon coating layer.
Wherein the liquid metal is gallium-indium alloy, and the thickness of the shell structure is 10-20 nm; the grain diameter of the liquid metal is 500 nm-3 mu m, and the grain diameter of the micron silicon is 3-5 mu m; the carbon fiber has a length of 100 μm and a diameter of about 30-50 nm. In the cathode material, the total content of the carbon coating layer and the carbon nanofiber is 15%, the content of silicon is 42.5%, and the content of liquid metal is 42.5%. The bulk density of the negative electrode material is 4.15 g/cm3。
The preparation method of the anode material comprises the following steps:
firstly, taking 100 mg of room-temperature liquid metal, and ultrasonically dispersing the liquid metal in 200 mL of isopropanol for 0.5h, wherein the ultrasonic power is 200W;
secondly, adding 100 mg of micron silicon powder into the dispersion liquid, continuing ultrasound treatment for 2 hours to obtain uniform dispersion liquid, and drying at 70 ℃ for 6 hours to obtain a mixture of micron silicon and liquid metal;
and thirdly, placing the solid mixture obtained in the second step into a crucible, and adding methane into a tubular furnace to perform chemical vapor deposition. Under the protection of nitrogen, heating to 1000 ℃ at a heating rate of 10 ℃/min, keeping the temperature for 1h, cooling to 400 ℃ at a heating rate of 5 ℃/min, and finally cooling to room temperature to obtain the silicon cathode material.
The SEM image of the anode material prepared in this example is shown in fig. 2, and it can be seen from fig. 2 that: the interwoven carbon nanofibers are distributed among the active particles to establish a long-range conductive network.
Example 2
The difference from example 1 is:
the amount of silicon in micrometer range was adjusted to 200 mg, and the rest was the same as in example 1, and the description thereof is omitted. The bulk density of the negative electrode material is 3.89 g/cm3The total content of the carbon coating layer and the carbon nanofiber is 15%, the silicon content is 57%, the liquid metal content is 28%, and the length of the carbon fiber is 80-100 mu m.
Example 3
The difference from example 1 is:
the liquid metal is ultrasonically dispersed in isopropanol for 1h, and the rest is the same as the example 1, and the details are not repeated. The bulk density of the negative electrode material is 4.10 g/cm3The silicon content is 42.5%, the total content of the carbon coating layer and the carbon nanofiber is 18%, and the liquid metal content is 39.5%.
Example 4
The difference from example 1 is:
the temperature of the chemical vapor deposition was 900 ℃, and the rest was the same as example 1, and the description thereof is omitted. The bulk density of the negative electrode material is 4.20 g/cm3The silicon content is 46%, the total content of the carbon coating layer and the carbon nanofiber is 8%, the content of the liquid metal is 46%, and the length of the carbon fiber is 50 mu m.
Example 5
The embodiment provides a lithium ion battery cathode material with a multilevel conductive structure, wherein the cathode material comprises active particles and carbon nanofibers dispersed among the active particles, the active particles comprise a core structure and a shell structure, the core structure comprises micron silicon and liquid metal, and the shell structure is a carbon coating layer.
Wherein the liquid metal is gallium indium tin alloy. The thickness of the shell structure is 10-20 nm; the grain diameter of the liquid metal is 500 nm-3 mu m, and the grain diameter of the micron silicon is 3-5 mu m; the carbon nanofibers have a length of 5 μm to 70 μm and a diameter of about 30 to 50 nm.
In the cathode material, the total content of the carbon coating layer and the carbon nanofiber is 10%, the silicon content is 45%, and the liquid metal content is 45%. The density of the negative electrode material is 4.10 g cm-3。
The preparation method of the anode material comprises the following steps:
firstly, taking 100 mg of room-temperature liquid metal, and ultrasonically dispersing the liquid metal in 200 mL of ethanol for 1h, wherein the ultrasonic power is 300W;
secondly, adding 100 mg of micron silicon powder into the dispersion liquid, continuing ultrasound treatment for 2 hours to obtain uniform dispersion liquid, and drying at 80 ℃ for 12 hours to obtain a mixture of micron silicon and liquid metal;
and thirdly, placing the solid mixture obtained in the second step in a crucible, and adding acetylene into a tubular furnace to perform chemical vapor deposition. Under the protection of argon, heating to 950 ℃ at a heating rate of 10 ℃/min, keeping the temperature for 1h, cooling to 400 ℃ at a heating rate of 5 ℃/min, and finally cooling to room temperature to obtain the silicon cathode material.
Example 6
The embodiment provides a lithium ion battery cathode material with a multilevel conductive structure, wherein the cathode material comprises active particles and carbon nanofibers dispersed among the active particles, the active particles comprise a core structure and a shell structure, the core structure comprises micron silicon and liquid metal, and the shell structure is a carbon coating layer.
Wherein the liquid metal is gallium indium tin alloy. The thickness of the shell structure is 10-20 nm; the grain diameter of the liquid metal is 500 nm-1 μm, and the grain diameter of the micron silicon is 3-5 μm; the carbon nanofibers have a length of 5 μm to 100 μm and a diameter of about 30 nm.
In the cathode material, the total content of the carbon coating layer and the carbon nanofiber is 15%, the content of silicon is 42.5%, and the content of liquid metal is 42.5%. The density of the negative electrode material is 4.15 g cm-3。
The preparation method of the anode material comprises the following steps:
firstly, taking 100 mg of room-temperature liquid metal, and ultrasonically dispersing the liquid metal in 200 mL of ethanol for 2 hours, wherein the ultrasonic power is 200W;
secondly, adding 100 mg of micron silicon powder into the dispersion liquid, continuing ultrasonic treatment for 1 hour to obtain uniform dispersion liquid, and drying at 85 ℃ for 15 hours to obtain a mixture of micron silicon and liquid metal;
and thirdly, placing the solid mixture obtained in the second step in a crucible, and adding acetylene into a tubular furnace to perform chemical vapor deposition. Under the protection of argon, heating to 980 ℃ at a heating rate of 10 ℃/min, keeping the temperature for 1h, cooling to 400 ℃ at a heating rate of 5 ℃/min, and finally cooling to room temperature to obtain the silicon cathode material.
Example 7
The embodiment provides a lithium ion battery cathode material with a multilevel conductive structure, wherein the cathode material comprises active particles and carbon nanofibers dispersed among the active particles, the active particles comprise a core structure and a shell structure, the core structure comprises micron silicon and liquid metal, and the shell structure is a carbon coating layer.
Wherein the liquid metal is gallium indium tin alloy. The thickness of the shell structure is 10-20 nm; the grain size of the liquid metal is 500 nm-800 nm, and the grain size of the micron silicon is 3-5 μm; the carbon nanofibers have a length of 5 μm to 50 μm and a diameter of about 30 nm.
In the cathode material, the total content of the carbon coating layer and the carbon nanofiber is 17%, the content of silicon is 42.5%, and the content of liquid metal is 40.5%. The density of the negative electrode material is 4.05 g cm-3。
The preparation method of the anode material comprises the following steps:
firstly, taking 100 mg of room-temperature liquid metal, and ultrasonically dispersing the liquid metal in 200 mL of ethanol for 3 hours, wherein the ultrasonic power is 250W;
secondly, adding 100 mg of micron silicon powder into the dispersion liquid, continuing ultrasonic treatment for 1.5 hours to obtain uniform dispersion liquid, and drying at 82 ℃ for 10 hours to obtain a mixture of micron silicon and liquid metal;
and thirdly, placing the solid mixture obtained in the second step in a crucible, and adding acetylene into a tubular furnace to perform chemical vapor deposition. Under the protection of argon, heating to 920 ℃ at a heating rate of 10 ℃/min, keeping the temperature for 1h, cooling to 400 ℃ at a heating rate of 9 ℃/min, and finally cooling to room temperature to obtain the silicon cathode material.
Example 8
The embodiment provides a lithium ion battery cathode material with a multilevel conductive structure, wherein the cathode material comprises active particles and carbon nanofibers dispersed among the active particles, the active particles comprise a core structure and a shell structure, the core structure comprises micron silicon and liquid metal, and the shell structure is a carbon coating layer.
Wherein the liquid metal is gallium indium tin alloy. The thickness of the shell structure is 10-20 nm; the grain size of the liquid metal is 500 nm-2 μm, and the grain size of the micron silicon is 3-5 μm; the carbon nanofibers have a length of 5 μm to 50 μm and a diameter of about 30 to 50 nm.
In the cathode material, the total content of the carbon coating layer and the carbon nanofiber is 5%, the silicon content is 47.5%, and the liquid metal content is 47.5%. The density of the negative electrode material is 4.20 g cm-3。
The preparation method of the anode material comprises the following steps:
firstly, taking 100 mg of room-temperature liquid metal, and ultrasonically dispersing the liquid metal in 200 mL of ethanol for 1h, wherein the ultrasonic power is 280W;
secondly, adding 100 mg of micron silicon powder into the dispersion liquid, continuing ultrasonic treatment for 1 hour to obtain uniform dispersion liquid, and drying at 78 ℃ for 18 hours to obtain a mixture of micron silicon and liquid metal;
and thirdly, placing the solid mixture obtained in the second step in a crucible, and adding acetylene into a tubular furnace to perform chemical vapor deposition. Under the protection of argon, heating to 940 ℃ at the heating rate of 10 ℃/min, keeping the temperature for 1h, then cooling to 400 ℃ at the heating rate of 5 ℃/min, and finally cooling to room temperature to obtain the silicon cathode material.
Example 9
The embodiment provides a lithium ion battery cathode material with a multilevel conductive structure, wherein the cathode material comprises active particles and carbon nanofibers dispersed among the active particles, the active particles comprise a core structure and a shell structure, the core structure comprises micron silicon and liquid metal, and the shell structure is a carbon coating layer.
Wherein the liquid metal is gallium indium tin alloy. The thickness of the shell structure is 10-20 nm; the grain size of the liquid metal is 500 nm-2 μm, and the grain size of the micron silicon is 3-5 μm; the carbon nanofibers have a length of 5 μm to 50 μm and a diameter of about 30 to 50 nm.
In the cathode material, the total content of the carbon coating layer and the carbon nanofiber is 5%, the silicon content is 46%, and the liquid metal content is 49%. The density of the negative electrode material is 4.20 g cm-3。
The preparation method of the anode material comprises the following steps:
firstly, taking 100 mg of room-temperature liquid metal, and ultrasonically dispersing the liquid metal in 200 mL of ethanol for 1.2h, wherein the ultrasonic power is 200W;
secondly, adding 100 mg of micron silicon powder into the dispersion liquid, continuing ultrasonic treatment for 1.2 hours to obtain uniform dispersion liquid, and drying at 88 ℃ for 20 hours to obtain a mixture of micron silicon and liquid metal;
and thirdly, placing the solid mixture obtained in the second step in a crucible, and adding acetylene into a tubular furnace to perform chemical vapor deposition. Under the protection of argon, heating to 970 at the heating rate of 10 ℃/min, keeping the temperature for 1h, then cooling to 400 ℃ at the heating rate of 5 ℃/min, and finally cooling to room temperature to obtain the silicon cathode material.
Example 10
The embodiment provides a lithium ion battery cathode material with a multilevel conductive structure, wherein the cathode material comprises active particles and carbon nanofibers dispersed among the active particles, the active particles comprise a core structure and a shell structure, the core structure comprises micron silicon and liquid metal, and the shell structure is a carbon coating layer.
Wherein the liquid metal is gallium indium tin alloy. The thickness of the shell structure is 10-20 nm; the grain diameter of the liquid metal is 500 nm-1 μm, and the grain diameter of the micron silicon is 3-5 μm; the carbon nanofibers have a length of 5 μm to 50 μm and a diameter of about 30 to 50 nm.
In the cathode material, the total content of the carbon coating layer and the carbon nanofiber is 5%, the silicon content is 47.5%, and the liquid metal content is 47.5%. The density of the negative electrode material is 4.20 g cm-3。
The preparation method of the anode material comprises the following steps:
firstly, taking 100 mg of room-temperature liquid metal, and ultrasonically dispersing the liquid metal in 200 mL of ethanol for 1.6h, wherein the ultrasonic power is 210W;
secondly, adding 100 mg of micron silicon powder into the dispersion liquid, continuing ultrasonic treatment for 1.7 hours to obtain uniform dispersion liquid, and drying at 84 ℃ for 17 hours to obtain a mixture of micron silicon and liquid metal;
and thirdly, placing the solid mixture obtained in the second step in a crucible, and adding acetylene into a tubular furnace to perform chemical vapor deposition. Under the protection of argon, heating to 950 ℃ at a heating rate of 10 ℃/min, keeping the temperature for 1h, then cooling to 400 ℃ at a heating rate of 5 ℃/min, and finally cooling to room temperature to obtain the silicon cathode material.
Comparative example 1
The difference from example 1 is that the amount of liquid metal used is 0 mg, and the rest is the same as example 1, and the description is omitted here. The carbon content in the material is 12 percent, and the block density is 1.5 g/cm3The silicon content was 88%.
The characteristic values of the anode materials obtained in experimental examples 1 to 10 and comparative example 1 were summarized as shown in table 1.
Table 1: test results of examples 1 to 10 and comparative example 1
Figure 156774DEST_PATH_IMAGE001
As can be seen from table 1: (1) as the liquid metal incorporation increases, the density increases and the length of the in situ generated carbon fibers increases. (2) With the increase of the introduction amount of the liquid metal, the temperature of the chemical vapor deposition is increased, the time is prolonged, and the content of the generated carbon material is increased. (3) Liquid metal of suitable particle size will catalyze the growth of carbon fibers of suitable content.
Mixing the negative electrode materials prepared in examples 1-10 with a binder (PAA) in a mass ratio of 8:2, and preparing a negative electrode sheet by using copper foil as a current collector; with LiPF6The lithium sheet is used as electrolyte, the lithium sheet is used as a positive electrode to form a half battery for electrochemical performance test, the serial numbers of the batteries are respectively S1-S10, and the mass specific capacity and the volume specific capacity of the battery are tested.
Mixing the negative electrode material prepared in the comparative example 1, a conductive additive (Super-P) and a binder (PAA) in a mass ratio of 4.25:4.25:2, and preparing a negative electrode sheet by using copper foil as a current collector; with LiPF6The lithium sheet is used as electrolyte, the lithium sheet is used as a positive electrode to form a half battery for electrochemical performance test, the battery number is D1, and the mass specific capacity and the volume specific capacity of the battery are tested.
The constant current charge and discharge curve of the battery with the number S1 is shown in fig. 3, and it can be seen from fig. 3 that: the composite material exhibits a higher capacity and a higher first coulombic efficiency.
The rate performance curve for the cell numbered S1 is shown in fig. 4, and can be seen from fig. 4: the composite material has high capacity under high current and shows good rate performance.
TABLE 2 Mass and volume specific capacities after cycling for a certain number of cycles for the batteries numbered S1-S10 and D1
Figure 473355DEST_PATH_IMAGE002
As can be seen from table 2: by accurately regulating and controlling the introduction amount of liquid metal, the negative electrode material with the optimal conductive structure can be obtained, and high volume performance (2100 mAh/cm) is obtained while high mass specific capacity (1200 mAh/g) is ensured3）。
Variations and modifications to the above-described embodiments may occur to those skilled in the art, which fall within the scope and spirit of the above description. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and variations of the present invention should fall within the scope of the claims of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims (10)

1. The lithium ion battery anode material with the multilevel conductive structure is characterized by comprising active particles and carbon nanofibers dispersed among the active particles, wherein the active particles comprise a core structure and a shell structure, the core structure comprises micron silicon and liquid metal, and the shell structure is a carbon coating layer.
2. The lithium ion battery anode material with the multilevel conductive structure according to claim 1, wherein: the liquid metal is gallium-indium alloy or gallium-indium-tin alloy.
3. The lithium ion battery anode material with the multilevel conductive structure according to claim 1, wherein: the thickness of the shell structure is 10-20 nm; the particle size of the liquid metal is 500 nm-3 mu m, and the particle size of the micron silicon is 3-5 mu m; the carbon nano-fiber has a length of 5-100 μm and a diameter of about 30-50 nm.
4. The lithium ion battery anode material with the multilevel conductive structure according to claim 1, wherein the total content of the carbon coating layer and the carbon nanofiber in the anode material is 5-18%, the silicon content is 40-50%, and the liquid metal content is 40-50%.
5. The lithium ion battery anode material with the multilevel conductive structure according to claim 1, wherein the density of the anode material is 4.10-4.20 g cm-3。
6. The preparation method of the lithium ion battery anode material with the multilevel conductive structure according to claim 1, characterized by comprising at least the following steps:
firstly, ultrasonically dispersing liquid metal in a solvent, adding micron silicon for continuous ultrasonic treatment to obtain uniform dispersion liquid, and centrifugally separating and drying to obtain a mixture of the micron silicon and the liquid metal;
and secondly, growing a carbon coating layer on the surface of the mixture formed by the micron silicon and the liquid metal by adopting a chemical vapor deposition method to form active particles, and growing carbon nano-fibers between the adjacent active particles to obtain the cathode material.
7. The preparation method of the multilevel-structure lithium ion battery anode material according to claim 6, wherein in the first step, the solvent is isopropanol or ethanol; the ultrasonic power is 200-300W, the ultrasonic time is 0.5-5h, the drying temperature is 70-90 ℃, and the drying duration is 2-24 h.
8. The preparation method of the lithium ion battery anode material with the multilevel structure according to claim 6, wherein in the second step, the chemical vapor deposition method comprises the following specific steps: under the protection of inert gas, placing the mixture of micron silicon and liquid metal in a corundum crucible, adding a carbon source into a tubular furnace, heating to 900-.
9. The method for preparing the lithium ion battery anode material with the multilevel structure according to claim 8, wherein the carbon source is at least one of methane or acetylene.
10. The method for preparing the multi-stage lithium ion battery anode material according to claim 8, wherein in the second step, the inert gas is argon or argon.
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