CN108063055B - Lithium ion capacitor - Google Patents

Lithium ion capacitor Download PDF

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CN108063055B
CN108063055B CN201711412193.1A CN201711412193A CN108063055B CN 108063055 B CN108063055 B CN 108063055B CN 201711412193 A CN201711412193 A CN 201711412193A CN 108063055 B CN108063055 B CN 108063055B
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graphite
expansion
lithium ion
ion capacitor
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CN108063055A (en
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林荣铨
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/04—Hybrid capacitors
    • H01G11/06—Hybrid capacitors with one of the electrodes allowing ions to be reversibly doped thereinto, e.g. lithium ion capacitors [LIC]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/24—Electrodes characterised by structural features of the materials making up or comprised in the electrodes, e.g. form, surface area or porosity; characterised by the structural features of powders or particles used therefor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/30—Electrodes characterised by their material
    • H01G11/32—Carbon-based
    • H01G11/38—Carbon pastes or blends; Binders or additives therein
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/30—Electrodes characterised by their material
    • H01G11/50—Electrodes characterised by their material specially adapted for lithium-ion capacitors, e.g. for lithium-doping or for intercalation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/84—Processes for the manufacture of hybrid or EDL capacitors, or components thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/84—Processes for the manufacture of hybrid or EDL capacitors, or components thereof
    • H01G11/86—Processes for the manufacture of hybrid or EDL capacitors, or components thereof specially adapted for electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/13—Energy storage using capacitors

Abstract

The invention discloses a lithium ion capacitor, which comprises a diaphragm, a lithium ion supply source and a shell, and also comprises a negative plate, a positive plate and lithium-containing organic electrolyte, wherein the negative plate uses a micro-expansion graphite material as a negative active material, the micro-expansion graphite material, graphite and polytetrafluoroethylene are uniformly mixed in distilled water according to the mass ratio of 90:9:15 to prepare slurry, the slurry is coated on the front surface and the back surface of a copper foil current collector, the copper foil current collector is placed into a vacuum drying box to be dried for 12 hours at 60 ℃, the dried electrode plate is taken out and pressed on a double-roller machine to form the electrode plate with the thickness of about 0.5mm, and then the negative plate of the lithium ion capacitor can be obtained. The energy density, the power density and the cycling stability of the lithium ion capacitor adopting the micro-expanded graphite material as the cathode active material can be greatly improved.

Description

Lithium ion capacitor
Technical Field
The invention belongs to the field of electrochemistry, and particularly relates to a lithium ion capacitor.
Background
The negative electrode of a Lithium-ion capacitor (LIC) is graphite pre-embedded with Lithium, so that the Lithium-ion capacitor is actually an asymmetric capacitor with different charging and discharging principles of the positive electrode and the negative electrode, combines the advantages of a super capacitor and a Lithium-ion battery, has higher energy density and power density, and has wider application prospect.
The lithium ion capacitor has higher energy density and power density, and the charge and discharge current density required to be released in the application field of the lithium ion capacitor is generally higher than that of a lithium ion battery. When a graphite material which is commonly used as a negative electrode of a lithium ion battery is used as a negative electrode of a lithium ion capacitor, the graphite material is not suitable for large-current charging and discharging because of complete crystallization and high orientation, about 10% of expansion and contraction can be generated in the d002 direction along with the insertion and extraction of Li < + >, the layered structure is easy to damage, and the cycle life is poor; the graphite surface has more active positions, so that a compact and uniform Solid Electrolyte Interface (SEI) film is not easy to generate in the process of lithium intercalation for the first time, and the first irreversible capacity is higher; in addition, the graphite with a highly oriented layered structure is very sensitive to the electrolyte, so that the graphite has poor compatibility with the electrolyte and influences the cycle performance; ultimately affecting the energy density, output power, and cycle performance of the lithium ion capacitor. Therefore, the micro-expansion modification of the graphite material is a feasible method to provide a lithium ion capacitor negative electrode material with higher energy density, higher output power and excellent cycle performance, a preparation method thereof and a lithium ion capacitor adopting the micro-expansion graphite.
Meanwhile, the raw material used in the technology of preparing the micro-expanded graphite material by taking natural graphite as the raw material is generally crystalline large crystalline flake graphite, although the crystalline flake graphite has good collective orientation, the graphite material with poor orientation and good uniformity is required in the application of the battery material, the microcrystalline graphite has fine particles, poor orientation of the aggregate and good uniformity, the microcrystalline graphite can replace the crystalline flake graphite as the raw material for preparing the expanded graphite with better electrical property, the charging efficiency, the battery stability and the cycle performance can be greatly improved, but the electric capacity is reduced, and meanwhile, the expansion effect of the microcrystalline graphite is not good, so that the application of the expanded microcrystalline graphite as the negative electrode material of the lithium ion electrode is hindered. If the advantages of the crystalline flake graphite and the microcrystalline graphite can be combined, a novel micro-expansion graphite material with high capacity, high charge-discharge efficiency and good cycle rate performance is prepared, is of great importance to the research of the micro-expansion graphite material in future, and can also alleviate the difficulty of large-scale low-added-value utilization of the microcrystalline graphite in China.
Disclosure of Invention
The invention aims to provide a lithium ion capacitor aiming at the problems in the prior art.
The purpose of the invention is realized by the following technical scheme:
a lithium ion capacitor comprises a diaphragm, a lithium ion supply source and a shell, and also comprises a negative plate, a positive plate and a lithium-containing electrolyte, wherein:
the negative plate uses a micro-expansion graphite material as a negative active material, the micro-expansion graphite material, graphite and polytetrafluoroethylene are uniformly mixed in distilled water according to a mass ratio of 90:9:15 to prepare slurry, the slurry is coated on the front surface and the back surface of a copper foil current collector, the copper foil current collector is placed into a vacuum drying oven to be dried for 12 hours at 60 ℃, the dried copper foil current collector is taken out and an electrode plate is pressed on a double-roller machine to be about 0.5mm in thickness, and then the negative plate of the lithium ion capacitor is obtained;
the positive plate is prepared by mechanically grinding activated carbon powder and conductive carbon black according to the mass ratio of 9:1, fully mixing, adding a proper amount of polytetrafluoroethylene (accounting for 1% of the total mass) and distilled water, grinding and stirring into paste, coating a glass sheet on a foamed nickel current collector in a scraping way, drying the coated foamed nickel current collector in a vacuum drying oven at 60 ℃ for 12 hours, taking out after drying, and pressing an electrode sheet on a double-roller machine to form the positive plate with the thickness of about 0.5mm, thus obtaining the positive plate of the lithium ion capacitor;
a polypropylene diaphragm is clamped between the positive and negative pole pieces to assemble the lithium ion capacitor, and lithium nitrate aqueous solution with the concentration of 1mol/L is injected between the positive and negative pole pieces as electrolyte;
the negative plate is made of a micro-expansion graphite material with an expansion coefficient of 10-30 times, and the method comprises the following steps:
s1, ball milling flake graphite and microcrystalline graphite in a mass ratio of 2-3: 1 until the particle size is 200-300 meshes, and obtaining a mixture;
s2, placing the mixture obtained in the step S1 in a muffle furnace, slowly heating to 350-400 ℃ in an inert atmosphere, preserving heat for 10-30 min, and air-cooling to room temperature for later use;
s3, carrying out chemical intercalation treatment on the mixture subjected to the heat treatment of S2 to obtain expandable mixed graphite;
and S4, placing the expandable mixed graphite obtained in the step S3 into a graphite expansion furnace to expand at 400-500 ℃ to obtain the micro-expansion graphite material.
The invention creatively mixes and expands the microcrystalline graphite and the crystalline flake graphite to prepare the micro-expanded graphite material, the crystalline flake graphite and the microcrystalline graphite with proper mass ratio are fully mixed in the ball milling process, part of microcrystalline graphite particles can enter the crystalline flake graphite layers in the ball milling process and are fully mixed, heat treatment is carried out after mixing, the ball milling mixed material can be activated by the heat treatment, sublimable impurities in the raw materials can be treated, chemical intercalation treatment is carried out immediately after the heat treatment, the intercalation effect and the intercalation efficiency can be improved, and the subsequent expansion treatment process is more facilitated.
In the process of expansion treatment of the ball-milling mixture, the structures of the flake graphite and the microcrystalline graphite are different, the change of the expansion process is different, the inter-sheet distance of the flake graphite is enlarged in the expansion process of the flake graphite, the microcrystalline graphite is expanded to be flocculent, the structure of the mixture after expansion shows that the flocculent expanded microcrystalline graphite among the flake graphite is connected among the flake graphite layers, the structure of the flocculent microcrystalline graphite among the flake graphite layers is more favorable for conduction among electrons, and the mixture is more suitable to be used as a lithium ion electrode material, so that the charge-discharge capacity of the micro-expanded graphite material formed after expansion is improved, and the cycle performance and the rate discharge performance of the micro-expanded graphite material are improved.
Preferably, in step S1, the carbon content of the flake graphite is not less than 85%, and the microcrystalline graphite is chenzhou lutang graphite powder, and the carbon content is 70-80%.
Preferably, in the ball milling process of the step S1, the ball-to-material ratio is 3-5: 1, the ball milling time is 6-8 hours, and the rotating speed is 200-300 r/min.
Preferably, the inert atmosphere of step S2 is one of nitrogen and argon.
Preferably, the mixture in the step S2 is heated in a muffle furnace, the heating rate is 5-20 ℃/min, and the method adopts
Preferably, the chemical intercalation processing step of step S3 includes:
s31, mixing perchloric acid with the mixed powder obtained in the step S2 according to a liquid-solid ratio of 10-30: 1L/Kg of the mixture is mixed and stirred evenly;
s32, mixing the mixed powder with potassium permanganate according to a mass ratio of 1: 2-8, adding potassium permanganate, uniformly stirring at room temperature, heating to 30-60 ℃, and continuously stirring for reaction for 1-3.0 hours;
s33, adding deionized water to raise the temperature in the reaction device to 60-100 ℃, and continuing stirring for reaction for 1-3.0 hours;
s34, filtering, washing and drying the filtered substance to obtain the expandable mixed graphite.
Preferably, the step S4 of performing high temperature expansion in a graphite expansion furnace includes the steps of:
s41, feeding: a graphite swelling furnace is adopted, and the expansible mixed graphite is put into a hearth through a feed inlet, wherein the temperature of the feed inlet is 30 ℃, and the putting speed is 2 Kg/h;
s42, expansion: the expansion temperature of the hearth is 400-500 ℃, and the expansion time is controlled to be 5s by controlling the air speed;
s43, discharging: and (4) after the step S42 is finished, the temperature of the discharge port is 50 ℃, and then the micro-expanded graphite material is collected at the discharge port.
Compared with the prior art, the invention has the beneficial effects that:
(1) the invention adopts the microcrystalline graphite and the crystalline flake graphite to prepare the micro-expanded graphite material, the reserves of the microcrystalline graphite in China are large, the price is low, and the low-added-value utilization is mostly realized.
(2) The invention adopts microcrystalline graphite and crystalline flake graphite as raw materials, carries out micro-expansion treatment on the mixed material to obtain the micro-expanded graphite material, expands the graphite spacing while having high volume specific capacity, forms a micro-nano hole structure and prepares the micro-expanded graphite material with a certain multiple.
(3) In the process of expansion treatment of the ball-milling mixture, the structures of the flake graphite and the microcrystalline graphite are different, the expansion processes are different, the inter-lamellar spacing of the flake graphite is enlarged in the expansion process of the flake graphite, the microcrystalline graphite is expanded to form flocculent, the flocculent expanded microcrystalline graphite among the flake graphite is connected among flake graphite layers, the structure of the flocculent graphite among the graphite layers is more beneficial to conduction among electrons and is more suitable to be used as a lithium ion electrode material, the charge-discharge capacity of the micro-expanded graphite material formed after expansion is improved, and the cycle performance and the multiplying power discharge performance of the micro-expanded graphite material are improved.
(4) The micro-expansion graphite and the crystalline flake graphite of the invention, after micro-expansion treatment, cause internal defects such as graphite layer spacing expansion and micro-nano holes and the like, can effectively buffer the size change of the electrode material during charging and discharging, particularly during heavy current charging and discharging, reduce the damage to the electrode material and avoid the increase of irreversible capacity, so the micro-expansion graphite prepared by the invention has better cycle stability and rate capability, and can be used as the cathode of a lithium ion battery.
(5) The high-temperature expansion method adopted by the invention combines the traditional high-temperature expansion method with the graphite expansion furnace, adopts the optimal expansion temperature, and can effectively improve the stability of the product by controlling the raw materials and the process parameters around the expansion temperature.
(6) The method has the advantages of cheap raw materials, short production period, obvious social and economic benefits and easy realization of industrial production.
Drawings
FIG. 1 is a scanning electron microscope image of the micro-expanded graphite material obtained in example 1.
FIG. 2 is a structural view of a high-temperature graphite expansion furnace in examples 1 to 4.
Detailed Description
The invention is further illustrated by the following specific examples. The following examples are illustrative only and are not to be construed as unduly limiting the invention which may be embodied in many different forms as defined and covered by the summary of the invention. Reagents, compounds and apparatus employed in the present invention are conventional in the art unless otherwise indicated.
Example 1
The invention discloses a micro-expansion graphite material prepared by mixing microcrystalline graphite and crystalline flake graphite, which comprises the following steps: comprises a graphite expansion furnace, adopts a high-temperature expansion method, and comprises the following steps:
s1, taking a microcrystalline graphite raw material with 70% of carbon content and a crystalline graphite raw material with 85% of carbon content, wherein the mass ratio of the crystalline graphite to the crystalline graphite is 2:1, and crushing and grinding the crystalline graphite to obtain mixed graphite powder with the particle size of 300 meshes.
S2, placing the mixture obtained in the step S1 in a muffle furnace, slowly heating to 350 ℃ in a nitrogen atmosphere, preserving heat for 30min, and cooling in air to room temperature for later use.
S3, carrying out chemical intercalation treatment on the mixture after the heat treatment of S2 to obtain expandable mixed graphite, wherein the chemical intercalation treatment comprises the following specific steps:
s31, mixing perchloric acid and microcrystalline graphite powder according to a liquid-solid ratio of 10: 1L/Kg of the mixture is mixed and stirred evenly; s32, according to the mass ratio of the microcrystalline graphite powder to the strong oxidant of 2:1, adding a strong oxidant, uniformly stirring at room temperature, heating to 30 ℃, and continuously stirring for reaction for 3 hours; s33, adding deionized water to raise the temperature in the reaction device to 60 ℃, and continuing stirring for reaction for 3 hours; s34, filtering, and then washing and drying the filtered substance to obtain the expandable mixed graphite.
S4, placing the expandable mixed graphite obtained in the step S3 into a graphite expansion furnace to expand at 400 ℃ to obtain a micro-expansion graphite material; the method comprises the following specific steps:
s41, feeding: a graphite swelling furnace is adopted, and the expansible mixed graphite is put into a hearth through a feed inlet, wherein the temperature of the feed inlet is 30 ℃, and the putting speed is 2 Kg/h; s42, expansion: the expansion temperature of the hearth is 400 ℃, and the expansion time is controlled to be 5s by controlling the wind speed; s43, discharging: and (4) after the step S42 is finished, the temperature of the discharge port is 50 ℃, and then the micro-expanded graphite material is collected at the discharge port.
The scanning electron microscope image of the micro-expanded graphite material obtained in the embodiment is shown in fig. 1, the pore diameter distribution range of the obtained micro-expanded graphite material is 1-100 nm, and the specific surface area is 350m2(g), expansion factor of 21 times, resistivity of 1.32 x 10-3Ω.m。
Example 2
The invention discloses a micro-expansion graphite material prepared by mixing microcrystalline graphite and crystalline flake graphite, which comprises the following steps: comprises a graphite expansion furnace, adopts a high-temperature expansion method, and comprises the following steps:
s1, taking a microcrystalline graphite raw material with 75% of carbon content and a crystalline graphite raw material with 90% of carbon content, wherein the mass ratio of the crystalline graphite to the crystalline graphite is 2:1, and crushing and grinding the crystalline graphite to obtain mixed graphite powder with the particle size of 200 meshes;
s2, placing the mixture obtained in the step S1 in a muffle furnace, slowly heating to 400 ℃ in a nitrogen atmosphere, preserving heat for 10min, and cooling in air to room temperature for later use.
S3, carrying out chemical intercalation treatment on the mixture after the heat treatment of S2 to obtain expandable mixed graphite, wherein the chemical intercalation treatment comprises the following specific steps:
s31, mixing perchloric acid and microcrystalline graphite powder according to a liquid-solid ratio of 15: 1L/Kg of the mixture is mixed and stirred evenly; s32, according to the mass ratio of the microcrystalline graphite powder to the potassium permanganate of 4: 1 adding potassium permanganate, uniformly stirring at room temperature, heating to 40 ℃, and continuously stirring for reaction for 2 hours; s33, adding deionized water to raise the temperature in the reaction device to 70 ℃, and continuing stirring for reaction for 2 hours; s34, filtering, and then washing and drying the filtered substance to obtain the expandable mixed graphite.
S4, placing the expandable mixed graphite obtained in the step S3 into a graphite expansion furnace to expand at 500 ℃ to obtain a micro-expansion graphite material; the method comprises the following specific steps:
s41, feeding: a graphite swelling furnace is adopted, and the expansible mixed graphite is put into a hearth through a feed inlet, wherein the temperature of the feed inlet is 30 ℃, and the putting speed is 2 Kg/h; s42, expansion: the expansion temperature of the hearth is 500 ℃, and the expansion time is controlled to be 5s by controlling the wind speed; s43, discharging: and (4) after the step S42 is finished, the temperature of the discharge port is 50 ℃, and then the micro-expanded graphite material is collected at the discharge port.
The morphological characteristics and the structural analysis of the micro-expanded graphite material obtained in the embodiment are basically the same as the results obtained in the embodiment 1, the pore diameter distribution range of the obtained micro-expanded graphite material is 1-100 nm, and the specific surface area is 606m2G, expansion factor 23 times, resistivity 4.32 x 10-3Ω.m。
Example 3
The invention discloses a micro-expansion graphite material prepared by mixing microcrystalline graphite and crystalline flake graphite, which comprises the following steps: comprises a graphite expansion furnace, adopts a high-temperature expansion method, and comprises the following steps:
s1, taking a microcrystalline graphite raw material with 75% of carbon content and a crystalline graphite raw material with 85% of carbon content, wherein the mass ratio of crystalline graphite to microcrystalline graphite is 2.5:1, and crushing and grinding the crystalline graphite to obtain mixed graphite powder with the particle size of 200 meshes;
s2, placing the mixture obtained in the step S1 in a muffle furnace, slowly heating to 400 ℃ in a nitrogen atmosphere, preserving heat for 10min, and cooling in air to room temperature for later use.
S3, carrying out chemical intercalation treatment on the mixture after the heat treatment of S2 to obtain expandable mixed graphite, wherein the chemical intercalation treatment comprises the following specific steps:
s31, mixing perchloric acid and microcrystalline graphite powder according to a liquid-solid ratio of 20: 1L/Kg of the mixture is mixed and stirred evenly; s32, according to the mass ratio of the microcrystalline graphite powder to the potassium permanganate of 6: 1 adding potassium permanganate, uniformly stirring at room temperature, heating to 50 ℃, and continuously stirring for reaction for 2 hours; s33, adding deionized water to raise the temperature in the reaction device to 80 ℃, and continuing stirring for reaction for 2 hours; s34, filtering, and then washing and drying the filtered substance to obtain the expandable mixed graphite.
S4, placing the expandable mixed graphite obtained in the step S3 into a graphite expansion furnace to expand at 450 ℃ to obtain a micro-expansion graphite material; the method comprises the following specific steps:
s41, feeding: a graphite swelling furnace is adopted, and the expansible mixed graphite is put into a hearth through a feed inlet, wherein the temperature of the feed inlet is 30 ℃, and the putting speed is 2 Kg/h; s42, expansion: the expansion temperature of the hearth is 450 ℃, and the expansion time is controlled to be 5s by controlling the wind speed; s43, discharging: and (4) after the step S42 is finished, the temperature of the discharge port is 50 ℃, and then the micro-expanded graphite material is collected at the discharge port.
The morphological characteristics and the structural analysis of the micro-expanded graphite material obtained in the embodiment are basically the same as the results obtained in the embodiment 1, the pore diameter distribution range of the obtained micro-expanded graphite material is 1-100 nm, and the specific surface area is 623m2G, expansion factor 18.1 times, resistivity 2.64 x 10-3Ω.m。
Example 4
The invention discloses a micro-expansion graphite material prepared by mixing microcrystalline graphite and crystalline flake graphite, which comprises the following steps: comprises a graphite expansion furnace, adopts a high-temperature expansion method, and comprises the following steps:
s1, taking a microcrystalline graphite raw material with 75% of carbon content and a crystalline graphite raw material with 90% of carbon content, wherein the mass ratio of crystalline graphite to microcrystalline graphite is 3:1, and crushing and grinding the crystalline graphite raw materials to obtain mixed graphite powder with the particle size of 300 meshes;
s2, placing the mixture obtained in the step S1 in a muffle furnace, slowly heating to 350 ℃ in a nitrogen atmosphere, preserving heat for 30min, and cooling in air to room temperature for later use.
S3, carrying out chemical intercalation treatment on the mixture after the heat treatment of S2 to obtain expandable mixed graphite, wherein the chemical intercalation treatment comprises the following specific steps:
s31, mixing perchloric acid and microcrystalline graphite powder according to a liquid-solid ratio of 20: 1L/Kg of the mixture is mixed and stirred evenly; s32, according to the mass ratio of the microcrystalline graphite powder to the potassium permanganate of 6: 1 adding potassium permanganate, uniformly stirring at room temperature, heating to 50 ℃, and continuously stirring for reaction for 2 hours; s33, adding deionized water to raise the temperature in the reaction device to 80 ℃, and continuing stirring for reaction for 2 hours; s34, filtering, and then washing and drying the filtered substance to obtain the expandable mixed graphite.
S4, placing the expandable mixed graphite obtained in the step S3 into a graphite expansion furnace to expand at 450 ℃ to obtain a micro-expansion graphite material; the method comprises the following specific steps:
s41, feeding: a graphite swelling furnace is adopted, and the expansible mixed graphite is put into a hearth through a feed inlet, wherein the temperature of the feed inlet is 30 ℃, and the putting speed is 2 Kg/h; s42, expansion: the expansion temperature of the hearth is 450 ℃, and the expansion time is controlled to be 5s by controlling the wind speed; s43, discharging: and (4) after the step S42 is finished, the temperature of the discharge port is 50 ℃, and then the micro-expanded graphite material is collected at the discharge port.
The morphological characteristics and the structural analysis of the micro-expanded graphite material obtained in the embodiment are basically the same as the results obtained in the embodiment 1, the pore diameter distribution range of the obtained micro-expanded graphite material is 1-100 nm, and the specific surface area is 492m2(g), expansion factor 18 times, resistivity 9.95 x 10-4Ω.m。
Example 5
Referring to fig. 2, the graphite expansion furnace used in the high temperature expansion process of examples 1 to 4 includes a furnace body 1, a feeding device 2, a discharging device 3 and a control device, wherein raw materials are fed into the furnace body 1 through the feeding device 2 and then collected through the discharging device 3; the discharging device 3 is arranged above the furnace body, and the feeding device 2 is arranged below the furnace body; the heating device 11 is arranged in the furnace body 1 and is heated by resistance wires, the airflow nozzle 4 is further arranged at the bottom in the furnace body 1, the airflow nozzle 4 further comprises an air source 41, an airflow pipeline 42 and an airflow control valve 43, the air source 41 is air and is connected with the airflow pipeline 42, the airflow pipeline 42 is connected with the airflow nozzle 4, the airflow control valve 43 is arranged in the airflow pipeline 42, the feeding device 2 is arranged above the airflow nozzle 4 and specifically adopts a spiral feeder, the control device comprises a processor 5 and a controller, the processor 5 is provided with a control panel and is connected with the controller, the controller comprises a first controller 53, a second controller 52 and a third controller 51, the first controller 53 is connected with the airflow control valve 43 of the airflow nozzle 4, the second controller 52 is connected with the feeding device 2, and the third controller 51 is connected with the heating device 11;
the processor 5 adopts a microprocessor, the first controller adopts an air inlet valve driving circuit, the second controller adopts a charging valve driving circuit, and the third controller adopts a heating driving circuit.
A cooling device 7 is also arranged between the discharging device 3 and the furnace body 1, the cooling device 7 comprises a heat exchange tube 71 and a water cooling tube 72, one end of the heat exchange tube 71 is connected with the furnace body 1, the other end of the heat exchange tube 71 is connected with the discharging device 3, the included angle between the heat exchange tube 71 and the horizontal line is 45-90 ℃, and the water cooling tube 72 is spirally arranged on the heat exchange tube 71;
the discharging device 3 comprises a plurality of storage bins 31 and connecting pipelines 32, one end of each connecting pipeline 32 is connected with a heat exchange pipe 71 and is provided with a cyclone separator 33, the other end of each connecting pipeline is connected with an exhaust port 34, and a plurality of branch pipelines 35 are further arranged on each connecting pipeline 32 and are respectively connected with the storage bins 31; the included angle between the connecting pipeline and the 32 horizontal line is 45-90 ℃;
still be equipped with agitator 8 in the furnace body 1, agitator 8 is spiral agitator for through motor and ball screw cooperation, make agitator 8 be linear motion from top to bottom in furnace body 1, thereby drive the air current backward flow in the furnace body 1.
Wherein: the temperature of the discharge hole is controlled through the cooling device, the heating device is also arranged in the feed hole to control the temperature of the feed hole, and the resistance wire 61 can be adopted to heat the discharge pipeline in the feeding device in the specific embodiment.
The time and the temperature of expansion can be controlled through a control panel, specifically, the air flow speed and the feeding speed are controlled by the processor through controlling the first controller and the second controller, so that the reaction time of the expansion of the intercalated graphite is controlled, the temperature of the heating device can be controlled by the third controller, the intellectualization of the expansion of the graphite is realized, and the accurate control is achieved.
The graphite expansion furnace is placed by adopting two layers of floors, the processing sequence of the raw materials is from bottom to top, the heat exchange tube and the connecting pipeline have certain included angles with a horizontal line, the problem of material clamping of the expanded graphite is solved through the cooperation of gravity and wind speed, the reaction yield is improved, and meanwhile, the occupied space is also solved by vertical placement.
The stirrer 8 is added in the furnace body 1 of the graphite expansion furnace, so that the air flow in the furnace body 1 forms convection, the uniform heating of the intercalated graphite is ensured, and the swelling reaction efficiency of the intercalated graphite is greatly improved.
Comparative example 1
Comparative example 1 differs from example 1 in that: comparative example 1 was not provided with step S2, and the other steps were the same as in example 1.
The pore diameter distribution range of the micro-expanded graphite material obtained in the comparative example 1 is 1-150 nm, and the specific surface area is 305m2(g), expansion factor 10, resistivity 9.95 x 10-2Ω.m。
Comparative example 2
Comparative example 2 differs from example 1 in that: comparative example 1, step S4 is different, and the other steps are the same as example 1, specifically:
and S4, heating and roasting the expandable mixed graphite obtained in the step S3 in an electric heating furnace at 400 ℃ in a nitrogen atmosphere for 60S to obtain the micro-expanded graphite material.
The pore diameter distribution range of the micro-expanded graphite material obtained in the comparative example 2 is 1-150 nm, and the specific surface area is 290m2G, expansion factor of 12.9, resistivity of 8.13 x 10-2Ω.m。
Comparative example 3
Comparative example 3 differs from example 1 in that: the raw materials of comparative example 3 are all microcrystalline graphite raw materials with carbon content of 70%, and are crushed and ground into graphite powder with granularity of 300 meshes. The other steps are the same as in example 1.
The pore diameter distribution range of the micro-expanded graphite material obtained in the comparative example 3 is 1-80 nm, and the specific surface area is 380m2G, expansion factor of 2.1 times, resistivity of 3.89 x 10-3Ω.m。
Comparative example 4
Comparative example 4 differs from example 1 in that: the raw materials of comparative example 4 are all flake graphite raw materials with 85% of carbon content, and are crushed and ground into graphite powder with the granularity of 300 meshes. The other steps are the same as in example 1.
The pore diameter distribution range of the micro-expanded graphite material obtained in the comparative example 4 is 1-300 nm, and the specific surface area is 169m2G, expansion factor of 30.5, resistivity of 8.14 x 10-3Ω.m。
Example 6
The invention provides a lithium ion battery.
A lithium ion capacitor comprises a diaphragm, a lithium ion supply source and a shell, and also comprises a negative plate, a positive plate and a lithium-containing organic electrolyte, wherein:
the negative plate uses the micro-expansion graphite material prepared in the embodiments 1 to 4 as a negative active material, the micro-expansion graphite material, graphite and polytetrafluoroethylene are uniformly mixed in distilled water according to the mass ratio of 90:9:15 to prepare slurry, the slurry is coated on the front surface and the back surface of a copper foil current collector, the slurry is placed into a vacuum drying oven to be dried for 12 hours at the temperature of 60 ℃, the dried slurry is taken out and an electrode plate is pressed on a double-roller machine to form the negative plate with the thickness of about 0.5mm, and then the negative plate of the lithium ion capacitor can be obtained;
the positive plate is prepared by mechanically grinding activated carbon powder and conductive carbon black according to the mass ratio of 9:1, fully mixing, adding a proper amount of polytetrafluoroethylene (accounting for 1% of the total mass) and distilled water, grinding and stirring into paste, coating a glass sheet on a foamed nickel current collector in a scraping way, drying the coated foamed nickel current collector in a vacuum drying oven at 60 ℃ for 12 hours, taking out after drying, and pressing an electrode sheet on a double-roller machine to form the positive plate with the thickness of about 0.5mm, thus obtaining the positive plate of the lithium ion capacitor;
a polypropylene diaphragm is clamped between the positive and negative pole pieces to assemble the lithium ion capacitor, and lithium nitrate aqueous solution with the concentration of 1mol/L is injected between the positive and negative pole pieces as electrolyte;
the capacitor assembling method comprises the following steps:
and a battery diaphragm is clamped between the positive and negative electrode plates, then the positive and negative electrode plates are clamped by a porous organic glass plate and fixed by a polytetrafluoroethylene screw, and the lithium ion capacitor is assembled.
The prepared lithium ion capacitor is subjected to electrochemical performance test for investigating the first charge-discharge performance and rate capability of the device and the charge-discharge cycle stability under high rate, and the steps are as follows: the assembled lithium ion capacitor is connected to an ArbinBT2000 battery tester, and after the lithium ion capacitor is firstly placed for about 12 hours, the lithium ion capacitor is charged to 3.8V according to the constant current of 0.5C multiplying power, then the lithium ion capacitor is charged at the constant voltage of 3.8V for 5 minutes, the lithium ion capacitor is discharged to 2.2V in the constant current mode, and the steps are repeated to test the capacitor. Wherein, the charging and discharging current used in the test of the cycle performance is 5C, and the test items and results are shown in Table 1.
TABLE 1
Figure GDA0002362257710000111
As can be seen from Table 1, the energy density, power density and cycling stability of the lithium ion capacitor using the micro-expanded graphite material of the invention as the negative active material can be greatly improved.
The inventor states that the invention is illustrated by the above embodiments, but the invention is not limited to the above detailed process equipment and process flow, i.e. the invention is not meant to be dependent on the above detailed process equipment and process flow. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims (7)

1. A lithium ion capacitor comprises a diaphragm, a lithium ion supply source and a shell, and is characterized by further comprising a negative plate, a positive plate and a lithium-containing electrolyte, wherein:
the negative plate uses a micro-expansion graphite material as a negative active material, the micro-expansion graphite material, graphite and polytetrafluoroethylene are uniformly mixed in distilled water according to a mass ratio of 90:9:15 to prepare slurry, the slurry is coated on the front surface and the back surface of a copper foil current collector, the copper foil current collector is placed into a vacuum drying oven to be dried for 12 hours at 60 ℃, the dried copper foil current collector is taken out and an electrode plate is pressed on a double-roller machine to form the negative plate with the thickness of 0.5mm, and then the negative plate of the lithium ion capacitor is obtained;
the positive plate is prepared by mechanically grinding activated carbon powder and conductive carbon black according to the mass ratio of 9:1, fully mixing, adding distilled water and polytetrafluoroethylene accounting for 1% of the total mass, grinding and stirring the mixture into paste, blade-coating the paste on a foam nickel current collector by using a glass sheet, drying the coated foam nickel current collector in a vacuum drying oven at 60 ℃ for 12 hours, taking out the dried foam nickel current collector, and pressing an electrode plate on a double-roller machine to form the positive plate with the thickness of 0.5mm, thus obtaining the positive plate of the lithium ion capacitor;
a polypropylene diaphragm is clamped between the positive and negative pole pieces to assemble the lithium ion capacitor, and lithium nitrate aqueous solution with the concentration of 1mol/L is injected between the positive and negative pole pieces as electrolyte;
the negative plate is made of a micro-expansion graphite material with an expansion coefficient of 10-30 times, and the method comprises the following steps:
s1, ball milling flake graphite and microcrystalline graphite in a mass ratio of 2-3: 1 until the particle size is 200-300 meshes, and obtaining a mixture;
s2, placing the mixture obtained in the step S1 in a muffle furnace, slowly heating to 350-400 ℃ in an inert atmosphere, preserving heat for 10-30 min, and air-cooling to room temperature for later use;
s3, carrying out chemical intercalation treatment on the mixture subjected to the heat treatment of S2 to obtain expandable mixed graphite;
and S4, placing the expandable mixed graphite obtained in the step S3 into a graphite expansion furnace to expand at 400-500 ℃ to obtain the micro-expansion graphite material.
2. The lithium ion capacitor of claim 1, wherein in step S1, the crystalline flake graphite contains not less than 85% of carbon, and the microcrystalline graphite is chenzhou lutang graphite powder, and the carbon content is 70-80%.
3. The lithium ion capacitor of claim 1, wherein in the ball milling process of step S1, the ball-to-material ratio is 3-5: 1, the ball milling time is 6-8 h, and the rotation speed is 200-300 r/min.
4. The lithium ion capacitor according to claim 1, wherein the inert atmosphere in step S2 is one of nitrogen and argon.
5. The lithium ion capacitor according to claim 1, wherein the mixture in step S2 is heated in a muffle furnace at a heating rate of 5-20 ℃/min.
6. The lithium ion capacitor according to claim 1,
step S3 the chemical intercalation process step includes:
s31, mixing perchloric acid with the mixed powder obtained in the step S2 according to a liquid-solid ratio of 10-30: 1L/Kg of the mixture is mixed and stirred evenly;
s32, mixing the mixed powder with potassium permanganate according to a mass ratio of 1: 2-8, adding potassium permanganate, uniformly stirring at room temperature, heating to 30-60 ℃, and continuously stirring for reaction for 1-3.0 hours;
s33, adding deionized water to raise the temperature in the reaction device to 60-100 ℃, and continuing stirring for reaction for 1-3.0 hours;
s34, filtering, washing and drying the filtered substance to obtain the expandable mixed graphite.
7. The lithium ion capacitor according to claim 1, wherein the step S4 of performing high temperature expansion in a graphite expansion furnace comprises the following steps:
s41, feeding: a graphite swelling furnace is adopted, and the expansible mixed graphite is put into a hearth through a feed inlet, wherein the temperature of the feed inlet is 30 ℃, and the putting speed is 2 Kg/h;
s42, expansion: the expansion temperature of the hearth is 400-500 ℃, and the expansion time is controlled to be 5s by controlling the air speed;
s43, discharging: and (4) after the step S42 is finished, the temperature of the discharge port is 50 ℃, and then the micro-expanded graphite material is collected at the discharge port.
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