CN108258198B - Graphene/carbon nanobelt three-dimensional structure electrode, preparation method thereof and application of graphene/carbon nanobelt three-dimensional structure electrode in energy storage battery electrode conductive network - Google Patents

Graphene/carbon nanobelt three-dimensional structure electrode, preparation method thereof and application of graphene/carbon nanobelt three-dimensional structure electrode in energy storage battery electrode conductive network Download PDF

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CN108258198B
CN108258198B CN201711418243.7A CN201711418243A CN108258198B CN 108258198 B CN108258198 B CN 108258198B CN 201711418243 A CN201711418243 A CN 201711418243A CN 108258198 B CN108258198 B CN 108258198B
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dimensional structure
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CN108258198A (en
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刘晓芳
高亮亮
水江澜
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Beihang University
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    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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    • Y02E60/10—Energy storage using batteries

Abstract

The invention discloses a graphene/carbon nanobelt three-dimensional structure electrode, a preparation method thereof and application of the graphene/carbon nanobelt three-dimensional structure electrode in an energy storage battery electrode conductive network, and belongs to the technical field of lithium ion batteries. According to the invention, by adopting a spray deposition and vacuum filtration method and controlling the proportion and content of the initially added Graphene Oxide (GO) and the carbon oxide nanoribbon (GONR), electrode materials with different multiplying power performances can be obtained. Graphene in the electrode with the graphene/carbon nanobelt three-dimensional structure is arranged in parallel, lithium iron phosphate particles prevent the graphene from agglomerating between layers, and meanwhile, the carbon oxide nanobelts are wound around the lithium iron phosphate particles; the mass fraction of graphene and carbon nanoribbons in the electrode after heat treatment is 2-5%; the prepared self-supporting material can be directly used as an electrode, and the electrode is more compact after being pressed by a tablet press.

Description

Graphene/carbon nanobelt three-dimensional structure electrode, preparation method thereof and application of graphene/carbon nanobelt three-dimensional structure electrode in energy storage battery electrode conductive network
Technical Field
The invention belongs to the technical field of lithium ion batteries, and relates to a graphene/carbon nanobelt three-dimensional structure electrode and a preparation method and application thereof.
Background
Lithium iron phosphate has attracted great interest as one of the most promising positive electrode materials for lithium ion batteries because of its low cost, low pollution, excellent cycle performance, good thermal stability, high safety and other advantages. However, the conductivity of the lithium iron phosphate material is low (10)-10S·m-1Order of magnitude) limits its large-scale commercialization especially in high-power applications. To solve this major problem, much effort has been madeIncluding metal ion doping, carbon coating, particle nanocrystallization, and the like. Among them, it seems that nanocrystallization of lithium iron phosphate particles is the most efficient method because it allows a transmission path of lithium ions to be greatly reduced while the surface area of the active material is greatly increased.
Unfortunately, while nanocrystallization of lithium iron phosphate particles can improve battery performance, the tap density of the material can also be greatly increased, which in turn leads to a reduction in volumetric energy density. The commercial lithium iron phosphate is generally micron-sized or submicron-sized powder, and the tap density of the commercial lithium iron phosphate is far greater than that of the commercial lithium iron phosphate prepared by a laboratory through hydrothermal method and the like. In addition, in the conventional electrode preparation process of the lithium ion battery, conductive additives such as conductive carbon black are generally required to be added to increase the conductivity of the system, and a binder and a current collector are required. These undoubtedly increase the mass and volume of the entire electrode.
Carbon nanoribbons (GNRs) are quasi-one-dimensional materials that are typically produced by opening carbon nanotubes lengthwise by chemical oxidation. Compared with carbon nanotubes as conductive materials, the carbon nanoribbons have high flexibility and larger available surface area.
Graphene (G) is a two-dimensional structure material, and is often used as a conductive additive and a support material in the energy field due to its advantages of large surface area, good conductivity, good chemical stability, and the like. The lithium iron phosphate and the graphene are mixed by a physical method, or the graphene is added in the synthesis process of the lithium iron phosphate, so that the lithium iron phosphate and the graphene can be mixed. But achieving an effective combination of high density and high energy is difficult. In addition, graphene-based self-supporting electrode materials can be prepared by Chemical Vapor Deposition (CVD), hydrothermal method, or the like, but the resulting material is at a disadvantage in volumetric energy density due to its porosity.
Self-supporting electrodes of graphene and active material can also be prepared by vacuum filtration, but it is difficult to commercialize lithium iron phosphate powder. This is because it is relatively easy to achieve uniform dispersion of graphene oxide in a polar solvent, but it is difficult to achieve commercial lithium iron phosphate particles having a relatively large size and density.
Disclosure of Invention
In order to solve the problems in the prior art, the invention combines spray deposition and vacuum filtration to prepare the graphene/carbon nanoribbon three-dimensional structure electrode, and provides a preparation method of the graphene/carbon nanoribbon three-dimensional structure electrode and application of the graphene/carbon nanoribbon three-dimensional structure electrode in an energy storage battery electrode conductive network. According to the invention, by adopting a spray deposition and vacuum filtration method and controlling the proportion and content of the initially added Graphene Oxide (GO) and the carbon oxide nanoribbon (GONR), electrode materials with different multiplying power performances can be obtained. The electrode with the graphene/carbon nanoribbon three-dimensional structure is characterized in that the graphene is arranged in parallel, lithium iron phosphate particles prevent the graphene from agglomerating between layers, and meanwhile, the carbon nanoribbon oxide is wound around the lithium iron phosphate particles; the mass fraction of graphene and carbon nanoribbons in the electrode after heat treatment is 2-5%; the prepared self-supporting material can be directly used as an electrode, and the electrode is more compact after being pressed by a tablet press.
The invention firstly provides a preparation method of a graphene/carbon nanobelt three-dimensional structure electrode, which comprises the following specific steps:
in the first step, a mixture of concentrated sulfuric acid and concentrated phosphoric acid is used as a solvent, potassium permanganate is used as an oxidant, and a carbon nanotube is opened along the length direction to form a carbon oxide nanoribbon (GONR). Unreacted potassium permanganate is reacted by hydrogen peroxide, and then the obtained product is separated by centrifugal separation and washed by deionized water for several times.
The volume ratio of the concentrated sulfuric acid to the concentrated phosphoric acid is 9: 1.
And secondly, respectively placing the carbon oxide nanobelt (GONR), the Graphene Oxide (GO) and the lithium iron phosphate (LFP) in a polar solvent, and then mixing and ultrasonically dispersing the mixture uniformly to obtain a mixed solution. Then the mixed solution is added into a bin of an air spraying device, and the mixed solution is sprayed on the vacuum-filtered filter membrane at a certain speed under a certain pressure.
The polar solvent is selected from N, N-Dimethylformamide (DMF), N-Dimethylacetamide (DMA), N-methyl-2-pyrrolidone (NMP) and the like.
The filter membrane is an organic filter membrane, such as a nylon filter membrane.
The condition parameters of the gas injection are as follows: the pressure is 5-20MPa, and the speed is 2-5 mL/min.
The mass ratio of the graphene oxide to the carbon oxide nanoribbon is 1:4-4: 1.
And thirdly, after spraying is finished, drying the filter membrane covered with the product, and then separating the product from the filter membrane. And (3) reducing the product at high temperature in argon-hydrogen atmosphere, and then pressing by a tablet press to obtain the graphene/carbon nanobelt three-dimensional composite electrode, which can be directly used as the anode of an energy storage battery.
The high-temperature reduction conditions are as follows: and (3) treating for 5 hours at 700 ℃ under an argon/hydrogen (V/V, 90/10) atmosphere.
The pressing pressure of the tablet press is 30-50 MPa.
The graphene/carbon nanoribbon three-dimensional structure electrode is directly used for an energy storage battery electrode conductive network, and the specific mass capacity of a half battery at 1C is 128-130 mAh.g-1And the specific capacity of 20C is 53-90 mAh.g < -1 >.
The invention has the advantages that:
1. the carbon nano tube is opened into the carbon nano belt along the length direction by adopting a chemical method, so that the flexibility of the material is increased, and meanwhile, the contact area between the carbon nano belt and the lithium iron phosphate is increased.
2. By adopting a spraying mode, the uniform dispersion of the lithium iron phosphate, the graphene oxide and the carbon oxide nanoribbons at the micron level can be realized. The effect of vacuum filtration can guarantee that the liquid in the spray droplets is removed quickly as soon as the liquid contacts the filter cake, and simultaneously guarantee the ductility of the graphene oxide as far as possible, and can increase the compactness of the electrode.
3. The mode of combining the graphene oxide and the carbon oxide nanobelts has the advantages that the graphene oxide is the main component for keeping the integrity and the mechanical property of the electrode, and the graphene oxide nanobelts can provide a conductive network for lithium iron phosphate particles which cannot be contacted by the graphene due to the flexibility and the quasi-one-dimensional characteristic of the graphene oxide nanobelts.
4. The product still needs to be compressed by a tablet press after being thermally reduced to further increase the compactness of the material.
Drawings
Fig. 1 is a schematic diagram of a three-dimensional structure of graphene/carbon nanoribbons prepared by the present invention.
Fig. 2 is a transmission electron microscope image of the carbon nanotubes used in the present invention and the prepared carbon oxide nanoribbons.
Fig. 3 is a scanning electron microscope image of a cross section of the composite electrode having a graphene/carbon nanoribbon three-dimensional structure prepared in example 1.
FIGS. 4 (a) to (d) show the rate capability of the three-dimensional electrodes prepared in examples 1 to 3 and the rate capability of the electrode prepared by the conventional doctor blade method.
Detailed Description
The invention is further described below with reference to the accompanying drawings and specific embodiments.
Example 1:
preparing a graphene/carbon nanobelt three-dimensional composite electrode (mass ratio m)GO:mGONR＝2.5:2.5)：
(1) Adding 36mL of concentrated sulfuric acid and 4mL of concentrated phosphoric acid into a three-neck flask, adding 200mg of carbon nano tubes, carrying out ultrasonic treatment for 0.5h, and mechanically stirring for 2 h. Slowly add 1g of potassium permanganate and stir at room temperature for 1 h. Then the temperature is increased to 75 ℃ and the reaction is carried out for 2 h. After the reaction, purification was performed. The purification specifically comprises the following steps:
first, the heat source was removed, cooled to room temperature, and then 10mL of H containing 35% by mass of 10mL was added2O2The unreacted potassium permanganate is reacted off. Then, centrifugation (10000rpm, 30min) was carried out to obtain GONR as a solid. The obtained GONR solid was washed 3 times with deionized water.
As shown in fig. 2, the carbon nanotubes used were opened in the length direction to obtain carbon oxide nanoribbons.
(2) The preparation concentration is 1mg mL-1The graphene oxide-N, N-Dimethylformamide (DMF) solution and the concentration of the solution are 1mgmL-1The oxidized carbon nanobelt-N, N-Dimethylformamide (DMF) solution of (b). Will 9Commercial lithium iron phosphate powder (8 mg) was added to 40mL of N, N-Dimethylformamide (DMF) solution and stirred magnetically. Then slowly dropwise adding 2.5mL of graphene oxide-DMF solution and 2.5mL carbon oxide nanoribbons-And (4) carrying out ultrasonic treatment on the DMF solution for 10min to obtain a mixed solution. Then adding the mixed solution into a storage bin of a spraying device, and spraying air onto the nylon filter membrane subjected to vacuum filtration. The gas injection feeding speed is 2mL/min, and the gas injection pressure is 5 MPa.
(3) And after spraying is finished, drying the filter membrane covered with the product in an oven at 40 ℃, tearing the product off in a large scale, and reducing the torn sample in a tube furnace at high temperature. The high-temperature reduction conditions are as follows: and (3) treating for 5 hours at 700 ℃ under an argon/hydrogen (V/V, 90/10) atmosphere. The obtained material is compacted by a tablet machine under the pressure of 30MPa to obtain the graphene/carbon nanobelt three-dimensional composite electrode which can be directly used as the anode of a battery. As shown in fig. 1, the graphene is spread and arranged in parallel, the nanobelts are coated on the graphene particles, and a conductive bridge is built between the graphene and the lithium iron phosphate particles.
Example 2:
preparing a graphene/carbon nanobelt three-dimensional composite electrode (mass ratio m)GO：mGONR＝4:1)：
(1) 36mL of concentrated sulfuric acid and 4mL of concentrated phosphoric acid are added into a three-neck flask, 200mg of carbon nano tubes are added, and ultrasonic treatment is carried out for 0.5 h. Mechanically stirred for 2 h. Slowly add 1g of potassium permanganate and stir at room temperature for 1 h. Then the temperature is increased to 75 ℃ and the reaction is carried out for 2 h. After the reaction, purification was performed. The purification specifically comprises the following steps:
first, the heat source was removed, cooled to room temperature, and then 10mL of H containing 35% by mass of 10mL was added2O2The ice-water mixture of (1). Then, centrifugation (10000rpm, 30min) was carried out to obtain GONR as a solid. The resulting solid was washed 3 times with deionized water.
(2) The preparation concentration is 1mg mL-1The graphene oxide-N, N-Dimethylformamide (DMF) solution and the concentration of the solution are 1mgmL-1The oxidized carbon nanobelt-N, N-Dimethylformamide (DMF) solution of (b). 98mg of commercial lithium iron phosphate powder was added to a 40ml N Dimethylformamide (DMF) solution and stirred magnetically. Then slowly dropwise adding4mL of graphene oxide DMF solution and 1mL of carbon oxide nanobelt DMF solution are subjected to ultrasonic treatment for 10 min. Then adding the mixture into a storage bin of a spraying device, and spraying air onto the nylon filter membrane subjected to vacuum filtration. The air jet feeding speed is about 5mL/min, and the air jet pressure is 20 MPa.
(3) And after spraying is finished, drying the filter membrane covered with the product in an oven at 40 ℃, tearing off the product in a large scale, and reducing the torn product in a tube furnace at high temperature. The high-temperature reduction conditions are as follows: and (3) treating for 5 hours at 700 ℃ under an argon/hydrogen (V/V, 90/10) atmosphere. After high-temperature reduction, the graphene/carbon nanobelt three-dimensional composite electrode is obtained after being pressed and compacted by a tablet machine under the pressure of 30MPa, and can be directly used as the anode of a battery.
Example 3
Preparation of graphene/carbon nanoribbon three-dimensional composite electrode (m)GO：mGONR＝1:4)：
(1) 36mL of concentrated sulfuric acid and 4mL of concentrated phosphoric acid are added into a three-neck flask, 200mg of carbon nano tubes are added, and ultrasonic treatment is carried out for 0.5 h. Mechanically stirred for 2 h. Slowly add 1g of potassium permanganate and stir at room temperature for 1 h. Then the temperature is increased to 75 ℃ and the reaction is carried out for 2 h. After the reaction, purification was performed. The purification specifically comprises the following steps:
first, the heat source was removed, cooled to room temperature, and then 10mL of H containing 35% by mass of 10mL was added2O2The ice-water mixture of (1). Then, centrifugation (10000rpm, 30min) was carried out to obtain GONR as a solid. The resulting solid was washed 3 times with deionized water.
(2) The preparation concentration is 1mg mL-1The graphene oxide-N, N-Dimethylformamide (DMF) solution and the concentration of the solution are 1mgmL-1The oxidized carbon nanobelt is a DMF solution. 98mg of commercial lithium iron phosphate powder was added to 40mL of N, N-Dimethylformamide (DMF) solution and stirred magnetically. Then slowly dripping 1mL of graphene oxide DMF solution and 4mL of carbon oxide nanobelt DMF solution, and carrying out ultrasonic treatment for 10 min. Then adding the mixture into a storage bin of a spraying device, and then spraying air onto a nylon filter membrane subjected to vacuum filtration. The feeding speed is about 2mL/min, and the air injection pressure is 5 MPa.
(3) After spraying, the filter membrane covered with the product is dried in an oven at 40 ℃ and the product can be torn off from the filter membrane in large pieces. And (4) reducing the torn product in a tube furnace at high temperature. The high-temperature reduction conditions are as follows: and (3) treating for 5 hours at 700 ℃ under an argon/hydrogen (V/V, 90/10) atmosphere. And compacting the product after high-temperature reduction by a tablet machine under the pressure of 50MPa to obtain the graphene/carbon nanobelt three-dimensional composite electrode, which can be directly used as the anode of a battery.
The electrode density after compaction in example 1 reached 2.50mg/cm3. As shown in fig. 3, is a scanning electron microscope image of the prepared graphene/carbon nanoribbon three-dimensional structure electrode. As can be seen from the figure, the graphene is arranged in parallel; and the carbon nanoribbons are arranged between the graphene sheets and coated on the surface of the lithium iron phosphate, and conductive bridges are erected between the lithium iron phosphate particles and the graphene. Meanwhile, we can also see that the lithium iron phosphate particles in the finally obtained product are very tightly packed. Taking a graphene/carbon nanobelt three-dimensional composite electrode with the mass of 4mg after compaction as a positive electrode, a lithium sheet as a negative electrode and LiPF with the concentration of 1M6A button cell (model 2032) was assembled in a glove box filled with argon gas using a mixed solvent of ethylene carbonate and dimethyl carbonate dissolved in a volume ratio of 1:1 as an electrolyte. The half-cell performance is shown in FIG. 4 (a), and the specific capacity at 1C is 130mAh g-1The specific capacity of 20C was 90mAh g-1 (the specific capacity was calculated based on the mass of the entire electrode).
Electrochemical properties of the three-dimensional structure electrode materials prepared in examples 2 and 3 are shown in (b) and (c) of fig. 4. The specific capacity of the graphene/carbon nanoribbon three-dimensional composite electrode 1C prepared in example 2 is 128mAh g-1And the specific capacity of 20C is 53 mAh.g-1. The specific capacity of the graphene/carbon nanoribbon three-dimensional composite electrode 1C prepared in example 3 is 129 mAh g-1And the specific capacity of 20C is 78 mAh.g-1. (specific capacity is calculated as the mass of the entire electrode).
Lithium iron phosphate according to the traditional process: acetylene black: PVDF (weight ratio) is mixed in a ratio of 8:1:1, N-methyl-2-pyrrolidone (NMP) is used as a solvent, the mixture is ground in a mortar for ten minutes, then a scraper is used for scraping the slurry onto an aluminum foil,drying the mixture in a vacuum oven at 110 ℃ for 5 hours. And (3) compacting by a tabletting machine under 30MPa, cutting into electrodes with the diameter of 12mm, loading 4mg, and assembling into the button cell in a glove box. The electrochemical properties are shown in FIG. 4 (d), and the specific capacity at 1C is 100mAh g-1And the specific capacity under 20C is 42 mAh.g-1(specific capacity is calculated as the mass of the entire electrode).
The traditional lithium iron phosphate electrode prepared by slurry scraping generally adopts acetylene black, super P and the like as conductive additives, and in view of the characteristic of poor conductivity of a lithium iron phosphate material, the proportion of the used conductive additives is generally 5% -10%. Due to the problems of low density of traditional conductive additives and more pores in the traditional slurry scraping mode, the compaction density of the traditional lithium iron phosphate electrode generally cannot exceed 2.2g cm-3. (the data calculated in this experiment was 1.9g cm-3). In the invention, graphene and carbon nanoribbons with excellent conductivity are used as conductive additives, and the proportion of the conductive additives is only 2%. And the electrode density is improved to 2.7mg cm by processes of suction filtration, subsequent compaction by a tablet press and the like-3. The lithium iron phosphate electrode designed by the invention has the advantages of compactness and good conductivity, and the specific mass capacity under 20 ℃ is 90mAh.g-1The volume specific capacity exceeds 240mAh cm-3Is far higher than that of the electrode prepared by the traditional method (the specific mass capacity is 42 mAh.g under 20C)-1Volume specific capacity of 80 mAh cm-3)。

Claims (8)

1. The preparation method of the graphene/carbon nanoribbon three-dimensional structure electrode is characterized by comprising the following steps: the specific steps are as follows,
the method comprises the following steps of firstly, opening a carbon nano tube along the length direction by taking a mixture of concentrated sulfuric acid and concentrated phosphoric acid as a solvent and potassium permanganate as an oxidant to form a carbon oxide nanoribbon GONR;
secondly, respectively placing the carbon oxide nanobelts, the graphene oxide and the lithium iron phosphate in a polar solvent, and then mixing and ultrasonically dispersing the carbon oxide nanobelts, the graphene oxide and the lithium iron phosphate uniformly to obtain a mixed solution; then adding the mixed solution into a storage bin of an air spraying device, and spraying the mixed solution onto the vacuum-filtered filter membrane;
thirdly, after spraying, drying the filter membrane covered with the product, and then separating the product from the filter membrane; and (3) reducing the product at a high temperature in an argon/hydrogen atmosphere, and then pressing the product by a tablet press to obtain the graphene/carbon nanobelt three-dimensional composite electrode.
2. The method for preparing the graphene/carbon nanoribbon three-dimensional structure electrode according to claim 1, wherein: in the first step, the volume ratio of the concentrated sulfuric acid to the concentrated phosphoric acid is 9: 1.
3. The method for preparing the graphene/carbon nanoribbon three-dimensional structure electrode according to claim 1, wherein: the first step is specifically that of the method,
adding 36mL of concentrated sulfuric acid and 4mL of concentrated phosphoric acid into a three-neck flask, adding 200mg of carbon nano tubes, carrying out ultrasonic treatment for 0.5h, and mechanically stirring for 2 h; slowly adding 1g of potassium permanganate, and stirring at room temperature for 1 h; then raising the temperature to 75 ℃ and reacting for 2 h; after the reaction is finished, purifying; the purification specifically comprises the following steps:
first, the heat source was removed, cooled to room temperature, and then 10mL of H containing 35% by mass of 10mL was added2O2Then carrying out centrifugal separation on the ice-water mixture to obtain GONR solid; the obtained GONR solid was washed 3 times with deionized water.
4. The method for preparing the graphene/carbon nanoribbon three-dimensional structure electrode according to claim 1, wherein: the polar solvent in the second step is N, N-dimethylformamide, N-dimethylacetamide or N-methyl-2-pyrrolidone; the filter membrane is a nylon filter membrane.
5. The method for preparing the graphene/carbon nanoribbon three-dimensional structure electrode according to claim 1, wherein: the condition parameters of the gas injection in the second step are as follows: the pressure is 5-20MPa, and the speed is 2-5 mL/min; the mass ratio of the graphene oxide to the carbon oxide nanoribbon is 1:4-4: 1.
6. The method for preparing the graphene/carbon nanoribbon three-dimensional structure electrode according to claim 1, wherein: the conditions of the high-temperature reduction in the third step are as follows: treating at 700 ℃ for 5h in argon/hydrogen atmosphere with the volume ratio of 90: 10; the pressing pressure of the tablet press is 30-50 MPa.
7. A three-dimensional structure electrode of graphite alkene/carbon nanoribbon which characterized in that: the electrode density reaches 2.50mg/cm3The graphene is spread and arranged in parallel, the nanobelts are coated on the graphene particles, and a conductive bridge is erected between the graphene and the lithium iron phosphate particles.
8. The use of the graphene/carbon nanoribbon three-dimensional structure electrode according to claim 7, wherein: the graphene/carbon nanoribbon three-dimensional structure electrode is directly used as the anode of an energy storage battery, and the specific mass capacity of a half battery under 1C is 128-130 mAh-1And the specific capacity of 20C is 53-90 mAh.g-1。
CN201711418243.7A 2017-12-25 2017-12-25 Graphene/carbon nanobelt three-dimensional structure electrode, preparation method thereof and application of graphene/carbon nanobelt three-dimensional structure electrode in energy storage battery electrode conductive network Expired - Fee Related CN108258198B (en)

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