CN115784226A - Method for regulating graphite microstructure and lithium storage performance by high-current pulsed electron beam - Google Patents
Method for regulating graphite microstructure and lithium storage performance by high-current pulsed electron beam Download PDFInfo
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 47
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Abstract
The invention discloses a method for regulating and controlling a graphite microstructure and lithium storage performance by a high-current pulsed electron beam, which comprises the following steps of firstly selecting natural graphite or an artificial graphite material; then placing the stainless steel shell body containing natural graphite or artificial graphite on an electron beam platform, starting the equipment, starting a vacuum system, when the vacuum degree reaches a specified value, sequentially starting a magnetic field, a spark source and cathode high voltage, and enabling a high-current pulse electron beam to directly irradiate the natural graphite or the artificial graphite to finish graphite modification. According to the invention, the natural graphite or the artificial graphite is modified by using the strong current pulsed electron beam, so that lithium storage active sites are increased, the intercalation and de-intercalation of lithium ions are smoother, the rapid transmission and charge storage capacity of the lithium ions are enhanced, and the bottleneck that the lithium storage capacity and the rate capability of the graphite are improved due to structural limitation is broken through. The problem of electrode material failure caused by the co-intercalation of solvated lithium ions is solved, the shuttling resistance of the lithium ions in the electrode is reduced, the volume expansion is small, the cycle performance is relatively stable, and the problem of reduced charge-discharge cycle stability of natural graphite and artificial graphite is solved.
Description
Technical Field
The invention belongs to the field of preparation of lithium battery cathode materials, and relates to a method for regulating and controlling a graphite microstructure and lithium storage performance by a high-current pulse electron beam.
Background
With the rapid development of the fields of new energy electric vehicles, artificial intelligence and the like, the requirements on the energy density and the power density of the lithium ion battery are increasing day by day. The lithium ion negative electrode material is one of the core components of the lithium ion battery, and the structure and the properties of the lithium ion negative electrode material play a key role in the performance of the battery.
The natural graphite is a multi-bond crystal, has a layered crystal structure, has good electric conductivity, heat conductivity and chemical stability, has large lithium storage capacity and rich resource reserves, and is one of the main cathode materials of the lithium battery. The surface of the natural graphite is rough and loose, so that the natural graphite has poor intermiscibility with electrolyte, and poor circulation stability caused by the co-intercalation of solvent molecules in the charge-discharge circulation process. Under the current density of 0.2C, the lithium storage capacity of the natural graphite electrode charged for the first time is 345.5mAh/g, the first coulombic efficiency is 85.5%, the reversible capacity of the natural graphite electrode is reduced to 304.2mAh/g after 200 cycles, and the reversible capacity of the natural graphite electrode is attenuated to 122.5mAh/g after 500 cycles.
The artificial graphite negative electrode material has good conductivity, a layered structure suitable for lithium intercalation and deintercalation, low price, wide sources and other comprehensive factors, and is the most widely applied negative electrode material of the lithium battery at present. The artificial graphite is prepared by a graphitization process under a high temperature condition, the main material is needle coke with a carbon material with an obvious fibrous structure, the needle coke has good thermal conductivity and electrical conductivity, and the artificial graphite has few undesirable impurities, few surface defects and few active sites for reacting with an electrolyte. Under the current density of 0.2C, the lithium storage capacity of the artificial graphite electrode for the first charging is 362mAh/g, the first coulombic efficiency is 90.1%, the capacity of the artificial graphite electrode is kept at 360mAh/g after 500 cycles, and the artificial graphite electrode has high charge-discharge cycle stability
However, the theoretical lithium storage capacity of the graphite is only 372 mAh/g, and the exertion of the rate capability of the graphite is limited by the regular layered structure, so that the improvement of the energy density and the power of the lithium ion battery is restricted to a great extent. In order to exert the lithium storage performance, the cycling stability performance and the conductivity of the graphite to the maximum extent, the modification treatment is mainly carried out on the graphite microstructure.
Currently, there are two types of mainstream methods for modifying the structure of graphite negative electrode materials: firstly, the spacing between graphite layers is enlarged, and the graphite dimension is reduced; secondly, the defects are built on the graphite structure. And stripping the graphite by a chemical method, and introducing structural defects to form a defective graphene structure. The graphene prepared by the chemical method is used as a lithium battery cathode material, can greatly improve the lithium storage capacity and lithium storage capacity of the battery, and has the advantages of good multiplying power and the like. However, graphene lithium storage also has disadvantages: aggregation and stacking can occur due to van der waals force, so that the lithium storage capacity of the graphene is rapidly attenuated, the defect graphene contains more oxygen-containing functional groups, the conductivity of the graphene is not good, and the decomposition of the oxygen-containing functional groups influences the charge-discharge cycle stability of the electrode. High-energy beam irradiation is taken as a typical physical method, the surface of a material is directly irradiated by high-energy beams, compared with a chemical method, specific reducing agents, oxidizing agents and other intermediate media are not required to be introduced, and impurities cannot be introduced after modification is completed. By using high energy beams such as laser beams and ion beams, defects can be built in situ on the graphite structure, but graphite interlayer peeling cannot be realized. In order to effectively solve the problem that the existing graphite modification method cannot solve, the graphite modification needs to be researched from different angles and methods.
Currently, the modification of material surfaces using high current pulsed electron beams is a new trend. The electron beam irradiates the material in a vacuum environment, high-energy and high-density electrons of the electron beam act on the surface of the material, and the deposition energy is maximum at 1/3 of the maximum range of the electron beam. The electron beam is irradiated on the graphite material, high-energy and high-density electrons induce the interior of graphite particles to expand, so that the distance between graphite layers can be instantly expanded, the defects that van der Waals force between graphite layers forms lamellar separation and irradiation generates high-temperature induction are overcome, and the lithium storage capacity of the graphite cathode material can be obviously improved, therefore, the feasibility is realized by adopting a high-current pulse electron beam to regulate and control the microstructure and the lithium storage performance of natural graphite or artificial graphite.
Disclosure of Invention
In order to overcome the defects of the conventional graphite cathode material modification technology, the invention provides a method for regulating and controlling the graphite microstructure and the lithium storage performance by using a high-current pulsed electron beam. Compared with the existing graphite cathode material modification method, the modification method provided by the invention has the advantages of simple modification process, environmental protection, no pollution, high efficiency, remarkably improved lithium storage capacity of the prepared lithium ion battery, and good cycle stability.
In order to achieve the purpose, the invention adopts the technical scheme that:
a method for regulating and controlling a graphite microstructure and lithium storage performance by a high-current pulsed electron beam comprises the following steps:
the first step is as follows: selecting natural graphite or artificial graphite material
Selecting a powdery solid pure natural graphite flake material, and selecting natural graphite with the average grain diameter of 12, 5 and 1 mu m;
selecting powdery solid artificial graphite material, wherein the particle size of the artificial graphite is concentrated to be more than 10 μm, so that the artificial graphite with the average particle size of 14 μm is selected;
pressing the selected natural graphite or artificial graphite material into a stainless steel shell for later use;
the second step is that: irradiating natural graphite or artificial graphite material by using high-current pulsed electron beam
Placing a stainless steel shell filled with natural graphite or artificial graphite on an electron beam platform, starting equipment, starting a vacuum system, and when the vacuum degree reaches a specified value, sequentially starting a magnetic field, a spark source and cathode high voltage to enable a high-current pulse electron beam to directly irradiate the natural graphite or the artificial graphite to finish graphite modification;
technological parameters of the high current pulse electron beam are as follows: degree of vacuum 4X 10 -3 ~8×10 -3 Pa, acceleration voltage of 20-30KV, pulse number of 3238 zxft Of 3238 and pulse duration of 1~5
s, energy density 2 to 3J/cm 2 ；
The above-mentionedThe technological parameters of the high current pulse electron beam are preferably as follows: vacuum degree of 6.5X 10 -3 Pa, acceleration voltage 25KV, pulse number of 1 time, pulse duration of 2
s, energy density 2.5J/cm 2 ；
The third step: lithium ion half-cell electrode preparation
Mixing an active material, a conductive agent and a binder according to a mass ratio of 91.6:1.8:6.6 mixing in a mortar, then adding an NMP solution, cleaning the copper foil by using absolute ethyl alcohol, opening a cabin of a coating machine, and flatly paving the copper foil on a cabin platform;
adjust the height of the scraper to 100
m, transferring the slurry onto the copper foil, starting a slurry coating program, closing a coating chamber after coating is finished, heating to 100 ℃, and preserving heat for 60min;
cooling the coating bin to a greenhouse, taking out the copper foil, compacting, and cutting into electrode plates with the diameter of 14 mm;
placing the electrode slice in a vacuum drying oven, drying at 80 ℃ for 24 hours, cooling to a greenhouse, taking out the electrode slice, and placing the electrode slice in a glove box;
the fourth step: lithium ion half cell assembly
The lithium ion half-cell is assembled in a glove box in argon atmosphere, and the assembly sequence comprises a positive electrode shell, an electrode plate, a polypropylene diaphragm, a lithium plate, a gasket, a spring piece and a negative electrode shell;
the electrolyte is formed by dissolving 1M LiPF6 in a solvent of ethylene carbonate and diethyl carbonate, ensuring that the electrolyte soaks each part of the battery in the battery assembling process, transferring the battery to a mold cavity of a battery packaging machine, sealing under 50MPa, wiping the battery clean, placing a self-sealing bag, and performing electrochemical performance test after activating a greenhouse for 24 hours.
Compared with the prior art, the invention has the beneficial effects that:
(1) The graphite modification process is simple and has high efficiency. The natural graphite powder and the artificial graphite are simply pressed into the shell to directly make the shellIrradiating with high current pulsed electron beam with pulse duration 2
The modification is completed, and the efficiency is high;
(2) The process is environment-friendly and pollution-free. According to the invention, the natural graphite or the artificial graphite is directly irradiated by the high-current pulse electron beam in the vacuum environment, chemical media such as an oxidant and a chemical agent are not needed, and impurities are not introduced;
(3) The lithium storage capacity and the rate capability are obviously improved. The high-current pulse electron beam is deposited by microsecond-level pulse energy, when natural graphite or artificial graphite is irradiated, a violent thermal stress effect is generated in the graphite material, the graphite interlayer spacing is increased, the graphite structure defects are increased, the defect types mainly comprise stone-wales and double-vacancy defects, and the lithium storage capacity and the rate capability of the graphite cathode are improved;
(4) The conductivity and the cycling stability are obviously improved. The natural graphite or the artificial graphite is modified by using the high-current pulsed electron beams, so that lithium storage active sites are increased, the intercalation and the deintercalation of lithium ions are smoother, and the rapid transfer and charge storage capacity of the lithium ions are enhanced. The problem of electrode material failure caused by the co-intercalation of solvated lithium ions is solved, the shuttling resistance of the lithium ions in the electrode is reduced, the volume expansion is small, the cycle performance is relatively stable, and the problem of reduced charge-discharge cycle stability of natural graphite and artificial graphite is solved.
Drawings
FIG. 1 is a scanning electron micrograph of natural graphite having particle diameters of 12 μm (G12), 5 μm (G5) and 1 μm (G1);
in FIG. 1, (a, b) G12, (c, d) G5, (e, f) G1;
FIG. 2 is a scanning electron microscope image of natural graphite with particle size of 12 μm after modification by irradiation of high current pulsed electron beam;
FIG. 3 is a scanning electron microscope image of natural graphite with a particle size of 5 μm after modification by irradiation of a high current pulsed electron beam;
FIG. 4 is a scanning electron microscope image of natural graphite with a particle size of 1 μm after modification by irradiation of a high current pulsed electron beam;
FIG. 5 is a graph of the cycling performance of natural graphite and M-G12 electrodes at a current density of 0.2C;
FIG. 6 is a scanning electron micrograph of pristine synthetic graphite;
FIG. 7 shows the energy density of artificial graphite 2J/cm 2 The modified graphite scanning electron microscope image is finished after the irradiation of the high-current pulse electron beam;
FIG. 8 shows the energy density of artificial graphite 2.5J/cm 2 The modified graphite scanning electron microscope image is finished after the irradiation of the high-current pulse electron beam;
FIG. 9 shows the energy density of the artificial graphite at 3J/cm 2 The modified graphite scanning electron microscope image is finished after the irradiation of the high-current pulse electron beam;
FIG. 10 is a graph of the cycling performance of the artificial graphite and MG-2.5 electrodes at a current density of 0.2C.
Detailed Description
The present invention will be described in more detail with reference to the accompanying drawings, which are not intended to limit the invention.
Example 1
A method for regulating and controlling a natural graphite microstructure and lithium storage performance by a high-current pulsed electron beam comprises the following steps:
(1) Natural graphite filled casing
The average particle diameter is 12
Weighing 2g of the powdery solid natural graphite material, placing the powdery solid natural graphite material into a stainless steel shell with the outer diameter of 20mm, the height of 2mm and the shell thickness of 0.25mm, and compacting by using 5MPa of pressure;
(2) Irradiation of natural graphite using high current pulsed electron beam
Placing the shell filled with the natural graphite on an electron beam platform, starting the equipment, and starting a vacuum system. When the vacuum degree reaches 6.5
10 -3 Pa, sequentially starting a magnetic field, a spark source and cathode high voltage to enable the high-current pulse electron beam to directly irradiate the natural graphite to complete the modification of the natural graphite;
high current pulse electron beam machineThe technological parameters are as follows: vacuum degree of 6.5X 10 -3 Pa, acceleration voltage 25KV, pulse number of 1 time, pulse duration of 2
s, energy density 2.5J/cm 2 Labeled M-G12;
(3) Lithium ion half-cell electrode preparation
Mixing a natural graphite active material, a conductive agent and a binder according to a mass ratio of 91.6:1.8:6.6 mixing in a mortar, adding an NMP solution, cleaning the copper foil by using absolute ethyl alcohol, opening a cabin of a coating machine, and flatly paving the copper foil on a cabin platform; adjust the height of the scraper to 100
Transferring the slurry onto a copper foil, starting a slurry coating program, closing a coating chamber after coating is finished, heating to 100 ℃, and keeping the temperature for 60min; cooling the coating bin to a greenhouse, taking out the copper foil, compacting, and cutting into electrode plates with the diameter of 14 mm; placing the electrode slice in a vacuum drying oven, drying at 80 ℃ for 24 hours, cooling to a greenhouse, taking out the electrode slice, and placing the electrode slice in a glove box;
(4) Lithium ion half cell assembly
The lithium ion half-cell is assembled in a glove box in argon atmosphere, and the assembly sequence comprises a positive electrode shell, an electrode plate, a polypropylene diaphragm, a lithium plate, a gasket, a spring piece and a negative electrode shell; the electrolyte is formed by dissolving 1M LiPF6 in a solvent of ethylene carbonate and diethyl carbonate, ensuring that the electrolyte soaks each part of the battery in the battery assembling process, transferring the battery to a mold cavity of a battery packaging machine, sealing under 50MPa, wiping the battery clean, placing a self-sealing bag, and performing electrochemical performance test after activating a greenhouse for 24 hours.
Example 2
A method for regulating and controlling a natural graphite microstructure and lithium storage performance by a high-current pulsed electron beam comprises the following steps:
(1) Natural graphite filled casing
The average particle diameter is 5
Weighing 2g of the powdery solid natural graphite material, placing the powdery solid natural graphite material into a stainless steel shell with the outer diameter of 20mm, the height of 2mm and the shell thickness of 0.25mm, and compacting by using 5MPa of pressure;
(2) Irradiation of natural graphite using high current pulsed electron beam
Placing the shell filled with the natural graphite on an electron beam platform, starting the equipment and starting a vacuum system. When the vacuum degree reaches 6.5
10 -3 Pa, sequentially starting a magnetic field, a spark source and cathode high voltage to enable the high-current pulse electron beam to directly irradiate the natural graphite to complete the modification of the natural graphite; technological parameters of the high current pulse electron beam are as follows: vacuum degree of 6.5X 10 -3 Pa, acceleration voltage 25KV, pulse number of 1 time, pulse duration of 2
Energy density of 2.5J/cm 2 Labeled M-G5;
(3) Lithium ion half cell electrode preparation and (4) lithium ion half cell assembly example 1 was followed.
Example 3
A method for regulating and controlling a natural graphite microstructure and lithium storage performance by a high-current pulsed electron beam comprises the following steps:
(1) Natural graphite filled casing
The average particle diameter is 1
Weighing 2g of the powdery solid natural graphite material, placing the powdery solid natural graphite material into a stainless steel shell with the outer diameter of 20mm, the height of 2mm and the shell thickness of 0.25mm, and compacting the powder by using 5MPa of pressure;
(2) Irradiation of natural graphite using high current pulsed electron beam
Placing the shell filled with the natural graphite on an electron beam platform, starting the equipment and starting a vacuum system. When the vacuum degree reaches 6.5
10 -3 Pa, sequentially starting a magnetic field, a spark source and cathode high voltage to enable the high-current pulse electron beam to directly irradiate the natural graphite to complete the modification of the natural graphite; the technological parameters of the high current pulse electron beam are that the vacuum degree is 6.5 multiplied by 10 -3 Pa, acceleration voltage 25KV, pulse number of 1 time, pulse duration of 2
Energy density of 2.5J/cm 2 Labeled M-G1;
(3) Lithium ion half cell electrode preparation and (4) lithium ion half cell assembly the same as example 1.
Modification effect of natural graphite
Passing energy density of 2.5J/cm 2 The average grain diameter of the natural graphite irradiated by the high-current pulse electron beam is 12
、5
、1
As shown in fig. 1, the modification effect is as follows:
the M-G12 graphite particles are obviously expanded, the particles become loose, gaps among the particles are reduced, the outline of the graphite disappears, the whole surface presents a hairy appearance, the graphite becomes a wrinkled lamellar structure, namely the graphite is converted into a defective graphene nano structure in situ, and the specific surface area of the M-G12 is obviously increased compared with that before modification, as shown in a schematic diagram 2; only a small amount of graphite particles of M-G5 generate expansion deformation, the thickness of the peeled graphite sheet is large, the wrinkled structure is less, only pits with micron-sized dimensions are found on the surface, and the graphite only generates local deformation, as shown in a schematic diagram 3; the electron beam penetrates through the graphite particles on the M-G1 surface layer to induce the graphite particles on the sub-surface layer to generate thermal expansion, so that the graphite particles on the surface layer are promoted to erupt, and finally, a pit shape is formed, as shown in a schematic diagram 4.
It can therefore be concluded that for graphite particles having a particle size larger than the penetration depth of the electron beam, energy is consumed inside the graphite particles, and conversely, electron beam energy is consumed between the graphite particles; secondly, the absorbed energy per unit volume distribution function is not uniform, and the electron beam energy is maximum at 1/3 of the penetration depth of the incident electrons.
The M-G12 with the most obvious modified natural graphite microstructure is prepared, the prepared lithium ion battery is detected, the first discharge capacity and the charge capacity of the M-G12 lithium battery are 494.5 mAh/G and 400.2 mAh/G respectively under the condition that the current density is 0.2C, and the corresponding coulombic efficiency is 80.9 percent. The reversible capacity is increased continuously along with the increase of the cycle number, the reversible capacity reaches 418.95 mAh/g after 200 cycles, the theoretical lithium storage capacity of the graphite is exceeded, the capacity is slightly reduced to 397.6 mAh/g after 500 cycles, and the retention rate is 94.5%, as shown in FIG. 5. After the natural graphite is modified by electron beams, the lithium storage capacity and the cycling stability are improved.
Example 4
A method for regulating and controlling the microstructure and lithium storage performance of artificial graphite by a high current pulsed electron beam comprises the following steps:
(1) Artificial graphite packing casing
Weighing 2g of powdery solid artificial graphite material with the average particle size of 14 mu m, placing the powdery solid artificial graphite material into a stainless steel shell with the outer diameter of 20mm, the height of 2mm and the shell thickness of 0.25mm, and compacting the solid artificial graphite material by using the pressure of 5 MPa;
(2) Irradiation of artificial graphite using high current pulsed electron beam
Placing the shell filled with the artificial graphite on an electron beam platform, starting equipment, starting a vacuum system, and when the vacuum degree reaches 6.5 multiplied by 10 < -3 > Pa, sequentially starting a magnetic field, a spark source and cathode high voltage to enable a high-current pulse electron beam to directly irradiate the artificial graphite to finish the modification of the artificial graphite; technological parameters of the high current pulse electron beam are as follows: vacuum degree of 6.5 × 10-3Pa, accelerating voltage of 25KV, pulse duration of 2 μ s, energy density of 2J/cm2, and mark as MG-2;
(3) Lithium ion half-cell electrode preparation
Mixing an artificial graphite active material, a conductive agent and a binder according to a mass ratio of 91.6:1.8:6.6 mixing in a mortar, adding an NMP solution, cleaning the copper foil by using absolute ethyl alcohol, opening a cabin of a coating machine, and flatly paving the copper foil on a cabin platform; adjusting the height of a scraper to be 100 mu m, transferring the slurry onto a copper foil, starting a slurry coating program, closing a coating chamber after coating is finished, heating to 100 ℃ and preserving heat for 60min. Cooling the coating bin to a greenhouse, taking out the copper foil, compacting, and cutting into electrode plates with the diameter of 14 mm; placing the electrode slice in a vacuum drying oven, drying at 80 ℃ for 24 hours, cooling to a greenhouse, taking out the electrode slice, and placing the electrode slice in a glove box;
(4) Lithium ion half cell assembly
The lithium ion half-cell is assembled in a glove box in argon atmosphere, and the assembly sequence comprises a positive electrode shell, an electrode plate, a polypropylene diaphragm, a lithium plate, a gasket, a spring piece and a negative electrode shell. The electrolyte is formed by dissolving 1M LiPF6 in a solvent of ethylene carbonate and diethyl carbonate, and the electrolyte is ensured to soak each part of the battery in the battery assembly process; transferring the battery to the inner cavity of a die of a battery packaging machine, sealing under 50MPa, wiping the battery clean, placing a self-sealing bag, activating in a greenhouse for 24 hours, and carrying out electrochemical performance test.
Example 5
A method for regulating and controlling the microstructure and lithium storage performance of artificial graphite by a high current pulsed electron beam comprises the following steps:
(1) Artificial graphite packing casing
Weighing 2g of powdery solid artificial graphite material with the average particle size of 14 mu m, placing the powdery solid artificial graphite material into a stainless steel shell with the outer diameter of 20mm, the height of 2mm and the shell thickness of 0.25mm, and compacting the powder artificial graphite material by using the pressure of 5 MPa;
(2) Irradiation of artificial graphite using high current pulsed electron beam
Placing the shell filled with the artificial graphite on an electron beam platform, starting equipment, starting a vacuum system, and when the vacuum degree reaches 6.5 multiplied by 10 < -3 > Pa, sequentially starting a magnetic field, a spark source and cathode high voltage to enable a high-current pulse electron beam to directly irradiate the artificial graphite to finish the modification of the artificial graphite; technological parameters of the high current pulse electron beam are as follows: vacuum degree of 6.5 × 10-3Pa, accelerating voltage of 25KV, pulse duration of 2 μ s, energy density of 2.5J/cm2, and mark MG-2.5;
(3) Lithium ion half cell electrode preparation and (4) lithium ion half cell assembly the same as example 4.
Example 6
A method for regulating and controlling the microstructure and lithium storage performance of artificial graphite by a high-current pulse electron beam comprises the following steps:
(1) Artificial graphite packing casing
Weighing 2g of powdery solid artificial graphite material with the average particle size of 14 mu m, placing the powdery solid artificial graphite material into a stainless steel shell with the outer diameter of 20mm, the height of 2mm and the shell thickness of 0.25mm, and compacting the powder artificial graphite material by using the pressure of 5 MPa;
(2) Irradiation of artificial graphite using high current pulsed electron beam
Placing the shell filled with the artificial graphite on an electron beam platform, starting equipment, starting a vacuum system, and when the vacuum degree reaches 6.5 multiplied by 10 < -3 > Pa, sequentially starting a magnetic field, a spark source and cathode high voltage to enable a high-current pulse electron beam to directly irradiate the artificial graphite to finish the modification of the artificial graphite; the technological parameters of the high current pulse electron beam are 6.5 multiplied by 10 < -3 > Pa, 25KV accelerating voltage, 2 mus pulse duration and 3J/cm < 2 > energy density, and are marked as MG-3;
(3) Lithium ion half cell electrode preparation and (4) lithium ion half cell assembly the same as example 4.
Modification effect of artificial graphite
Artificial graphite having an average particle diameter of 14 μm, as shown in FIG. 6, was subjected to examples 4 to 6 and had an energy density of 2J/cm 2 、2.5J/cm 2 、3J/cm 2 The modification effect of the high-current pulse electron beam irradiation is as follows:
MG-2 became matte in its surface but the graphite particle contours were still visible and the graphite particles were exfoliated into graphite flakes of non-uniform thickness, as shown in scheme 7; the MG-2.5 surface became fluffy, the contour of the graphite particles became blurred, the graphite particles were exfoliated into wrinkled graphite sheets, and an almost transparent structure was exhibited, as shown in fig. 8; significant ablation of the graphite surface and debris of graphite flakes remained on the surface, but significant exfoliation of the graphite flakes was observed, the particles were broken and the structure collapsed, as shown in scheme 9.
Therefore, it can be concluded that, in the process of graphite temperature rise caused by electron beam action, the induced thermal stress causes graphite exfoliation, and as irradiation progresses, the surface temperature continuously rises even exceeds the melting point of graphite, ablation, exfoliation, and disappearance of the outline of graphite particles occur.
The MG-2.5 with the most obvious microstructure of the modified artificial graphite is prepared, the prepared lithium ion battery is detected, the first discharge capacity and the charge capacity of the MG-2.5 lithium battery are 532.0 mAh/g and 431.6 mAh/g respectively under the condition that the current density is 0.2C, and the corresponding coulombic efficiency is 84.3 percent. Along with the increase of the circulation times, the specific capacity is continuously increased, the specific capacity reaches 450.5 mAh/g after 100 times of circulation and is kept stable, and the coulombic efficiency reaches 100 percent, as shown in figure 10. The lithium storage performance capacity of the lithium battery is greatly improved, and the cycle performance is stable.
The above-mentioned embodiments only represent the embodiments of the present invention, but they should not be understood as the limitation of the scope of the present invention, and it should be noted that those skilled in the art can make several variations and modifications without departing from the spirit of the present invention, which all fall into the protection scope of the present invention.
Claims (4)
1. A method for regulating and controlling a graphite microstructure and lithium storage performance by a high-current pulse electron beam is characterized by comprising the following steps:
the first step is as follows: selecting natural graphite or artificial graphite material
Pressing the selected natural graphite or artificial graphite material into a stainless steel shell for later use;
the second step: irradiating natural graphite or artificial graphite material by using high-current pulsed electron beam
Placing a stainless steel shell filled with natural graphite or artificial graphite on an electron beam platform, starting equipment, starting a vacuum system, and when the vacuum degree reaches a specified value, sequentially starting a magnetic field, a spark source and cathode high voltage to enable a high-current pulse electron beam to directly irradiate the natural graphite or the artificial graphite to finish graphite modification;
technological parameters of the high current pulse electron beam are as follows: degree of vacuum 4X 10 -3 ~8×10 -3 Pa, acceleration voltage of 20-30 KV, pulse frequency of 1~3 and pulse duration of 1~5
s, energy density 2 to 3J/cm 2 。
2. The method for regulating and controlling the microstructure and the lithium storage performance of graphite by the high-current pulsed electron beam according to claim 1, wherein the method comprises the following steps: the natural graphite is a powdery solid pure natural graphite flake material, and the natural graphite with the average grain diameter of 12, 5 and 1 mu m is selected.
3. The method for regulating and controlling the microstructure and lithium storage performance of graphite by the high current pulsed electron beam according to claim 1, wherein the method comprises the following steps: the artificial graphite is made of powdery solid artificial graphite material, and the average particle size of the artificial graphite is 14 mu m.
4. The method for regulating and controlling the microstructure and the lithium storage performance of graphite by the high-current pulsed electron beam according to claim 1, wherein the method comprises the following steps: the technological parameters of the high current pulse electron beam are as follows: vacuum degree of 6.5X 10 -3 Pa, acceleration voltage 25KV, pulse number of 1 time, pulse duration of 2
s, energy density 2.5J/cm 2 。
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