CN102874807A - Active carbon material and application of same serving as double-electric layer capacitor electrode material - Google Patents

Abstract

The invention discloses an active carbon material and application of the active carbon material serving as a double-electric layer capacitor electrode material. The active carbon material is prepared by a moso bamboo serving as a carbon source through a phosphoric acid-carbon dioxide physio-chemical activation method. The preparation method specifically comprises the following steps of: (1) getting moso bamboo sheets, adding same to a phosphoric acid solution to be fully dipped, then taking out the bamboo sheets to be dried; (2) transforming the phosphoric acid sheets obtained in step (1) into a tubular furnace, heating to reach 400 to 800 DEG C under N2 protection atmosphere, then switching into CO2 (Carbon Dioxide) atmosphere to activate for 1 to 4 hours at a constant temperature, and finally switching to the N2 protection atmosphere to be cooled to reach a room temperature; and (3) crushing and sieving the produced obtained in step (2), and washing through deionized water until the pH (Potential Of Hydrogen) of filtrate is more than 6; and then drying to obtain a active carbon material. The active carbon material prepared by the preparation method has aperture ranged from 2 to 5nm, and is capable of improving capacity of a capacitor while being used as a double-electric layer capacitor electrode material, and has an excellent performance of charging and discharging.

Description

Activated carbon materials and their applications as electrode materials for electric double layer capacitors

(1) Technical field

The invention relates to an activated carbon material and its application as an electrode material of an electric double layer capacitor.

(2) Background technology

Electric double layer capacitor (Electrochemical Double Layer Capacitor, referred to as EDLC) is a new type of energy storage device between traditional capacitors and batteries, with a specific power greater than 1kW/kg, even tens of kilowatts per kilogram), long life (more than 100,000 times), wide operating temperature (-40°C ~ 70°C) and fast charging (less than 3min), etc. These characteristics of electric double layer capacitors make it have a wide range of application prospects.

The electrode materials of electric double layer capacitors are mainly various high specific surface area carbon materials, such as activated carbon, carbon nanotubes and carbon aerogels. Activated carbon has become the most promising electrode material for industrialization due to its low price, abundant raw materials, and high electrochemical stability. However, the commercial activated carbons currently used in electric double layer capacitors are mainly various microporous carbons with high specific surface area. Electric double layer capacitors based on this microporous carbon have low specific capacitance.

(3) Contents of the invention

The first object of the present invention is to provide a medium and small pore activated carbon material with a pore diameter of 2-5nm, which can improve the capacitor capacity and has excellent charge and discharge performance when used as an electrode material for an electric double layer capacitor.

The second object of the present invention is to use the activated carbon material as an electrode material of an electric double layer capacitor to increase the capacity of the capacitor and obtain good charge and discharge performance.

The technical scheme of the present invention is described in detail below.

An activated carbon material, which is prepared by using moso bamboo as a carbon source by a phosphoric acid-carbon dioxide physical and chemical activation method, and its preparation method specifically includes the following steps:

(1) Take the moso bamboo slices, add phosphoric acid solution to fully soak them, take out the moso bamboo slices and dry them;

(2) Place the moso bamboo slices obtained in step (1) in a tube furnace, raise the temperature to 400-800°C under the protection of _N2 atmosphere, then switch to _CO2 atmosphere for constant temperature activation for 1-4h, and switch back to _N2 after the end Protected and cooled to room temperature;

(3) Grinding the product obtained in step (2), washing with deionized water until the pH value of the filtrate is greater than 6, and drying to obtain an activated carbon material.

In the step (1), phosphoric acid is used as a chemical activator, which is soaked into the moso bamboo by soaking. The addition of phosphoric acid can change the pyrolysis process of moso bamboo and facilitate hole expansion. The mass fraction of the phosphoric acid solution is preferably 40-85%, more preferably 60-85%; the mass ratio of phosphoric acid mass to moso bamboo chips is 2-4:1. In order to fully immerse the phosphoric acid into the moso bamboo, the moso bamboo can be cut into small bamboo pieces of a certain size (for example, small bamboo pieces with a length of 1 cm and a width of 0.5 cm), and during the soaking process, an appropriate amount of stirring can be used to mix them evenly. Usually, soaking is carried out at room temperature (25-30° C.), and the soaking time is 1-9 days, preferably 5-9 days.

In the step (2), the temperature is first raised to the reaction temperature under the protection of nitrogen, and the heating rate is preferably 5-10°C/min, and then switched to carbon dioxide gas, and the reaction is carried out with carbon dioxide as a physical activator, and the reaction temperature is 400-800 °C, the reaction time is 1-4 hours; preferably, the reaction temperature is 500-600 °C, and the reaction time is 3-4 h; more preferably, the reaction temperature is 500 °C, and the reaction time is 3 h. During the reaction process, the flow rate of carbon dioxide is usually controlled at 40~60cm ³ /min.

In the step (3), excess phosphoric acid is washed with deionized water to remove impurities. If necessary, it can be washed with hydrochloric acid and then washed with deionized water until neutral.

The invention also provides the activated carbon material as an electrode material of an electric double layer capacitor.

Compared with the prior art, the present invention has beneficial effects mainly reflected in:

The present invention adopts cheap moso bamboo waste as carbon source, carbon dioxide gas as physical activator, phosphoric acid as chemical activator, adopts combined physical and chemical activation method to prepare activated carbon material, the source of raw materials used is wide, easy to obtain, low in price, and easy to implement in industrialization; preparation; The process is simple, and there is no discharge of waste water and waste gas, so it is friendly to the environment; the electric double layer capacitor made of activated carbon material has high capacity and excellent charge and discharge performance.

(4) Description of drawings

Fig. 1 is the XRD diffractogram of activated carbon prepared by embodiment 1;

Fig. 2 is the scanning electron microscope (SEM) and the transmission electron microscope (TEM) photo of activated carbon prepared in embodiment 1;

Fig. 3 is the 77K nitrogen adsorption-desorption curve of activated carbon prepared in embodiment 1;

Fig. 4 is a charge-discharge curve diagram of the electric double layer capacitor prepared in Example 1, the voltage range is 0-0.8V, the charging current is 0.4A/g, and the measurement temperature is 25±5°C.

(5) Specific implementation methods

The technical solutions of the present invention will be further described below with specific examples, but the protection scope of the present invention is not limited thereto.

Example 1

Cut moso bamboo into small bamboo pieces about 1 cm long and 0.5 cm wide, mix phosphoric acid and moso bamboo slices with a mass fraction of 85% phosphoric acid solution and moso bamboo slices at a ratio of 4:1, soak at room temperature for 7 days, dry, and then place Quartz boat, heated up to 500°C at a heating rate of 5°C/min under the protection of nitrogen in a tube furnace, passed through carbon dioxide protection, and the flow rate was 40cm ³ /min, activated at a constant temperature of 500°C for 3 hours, then switched back to nitrogen atmosphere, and cooled to After room temperature, take it out and grind it through a 200-mesh sieve. Wash with deionized water until the pH of the filtrate is >6, put the product in a drying oven at 80°C and dry for 12 hours to obtain the activated carbon material.

Figure 1 is the XRD diffraction pattern of this material. Compared with the standard card, it can be seen that the diffraction peaks at 2θ about 22° and 43° are the 002 and 100 crystal planes of activated carbon, and the steamed bread peaks appearing in XRD indicate that activated carbon is amorphous.

Figure 2(a) is a scanning electron microscope photo of the material. It can be seen that the pores of activated carbon are circular, indicating that there are a large number of pores distributed. These pores are the main channels for electrolyte diffusion and capillary action in the electrode. Figure 2(b) is a transmission electron microscope photo of the material. It can be seen that activated carbon has many micropores and small mesopores with an average pore size between 2-5nm. These micropores and small mesopores play an important role in the formation of the electric double layer. important role.

Figure 3 is the adsorption-desorption curve of the material under 77K nitrogen gas. The isotherm adsorption curve does not overlap with the desorption curve, and has obvious hysteresis, indicating that there are a large number of mesopores in the sample, and the pore diameter is mainly concentrated in 2-5nm. The observations are consistent.

Make electrode with the activated carbon that embodiment 1 makes according to the following method:

Mix activated carbon with acetylene black and 60wt% polytetrafluoroethylene (PTFE) emulsion in a ratio of 85:10:5, and then apply it on a 20mm×20mm nickel foam, and hold the pressure at 15MPa for 30s on a powder tablet press , dried in a vacuum oven at 120°C for 12h. Using a polypropylene separator, the electrode sheet, separator, and polyethylene sheet were assembled into an electrochemical capacitor, which was soaked in 30% KOH electrolyte for 6 hours before testing.

Figure 4 is the multi-cycle constant current charge and discharge curve of the capacitor under the constant current of 0.4A/g. The charge and discharge curve has an obvious triangular symmetrical distribution, indicating that the reversibility of the electrode reaction is very good. In the constant current charge and discharge process, the voltage of the capacitor changes linearly with the charge and discharge time, indicating that the internal resistance of the electrode that accelerates the voltage drop is small, and the specific capacity of the capacitor can reach 190F/g.

Example 2

Cut moso bamboo into small bamboo pieces about 1 cm long and 0.5 cm wide, mix phosphoric acid and moso bamboo slices with a mass fraction of 85% phosphoric acid solution and moso bamboo slices at a ratio of 4:1, soak at room temperature for 7 days, dry, and then place The quartz boat was heated to 600°C at a heating rate of 5°C/min under the protection of nitrogen in a tube furnace, and then protected by carbon dioxide, with a flow rate of 40cm ³ /min. It was activated at a constant temperature of 600°C for 3 hours, then switched back to the nitrogen atmosphere, and cooled to After room temperature, take it out and grind it through a 200-mesh sieve. Wash with deionized water until the pH of the filtrate is >6, put the product in a drying oven at 80°C and dry for 12 hours to obtain the activated carbon material.

The activated carbon was used to make electrodes according to the method of Example 1, and assembled into an electric double layer capacitor, and its specific capacity reached 165F/g.

Example 3

Cut moso bamboo into small bamboo pieces about 1 cm long and 0.5 cm wide, mix phosphoric acid and moso bamboo slices with a mass fraction of 85% phosphoric acid solution and moso bamboo slices at a ratio of 3:1, soak at room temperature for 7 days, dry, and then place Quartz boat, heated up to 500°C at a heating rate of 5°C/min under the protection of nitrogen in a tube furnace, passed through carbon dioxide protection, the flow rate was 40cm ³ /min, activated at a constant temperature of 500°C for 4 hours, then switched back to the nitrogen atmosphere, and cooled to After room temperature, take it out and grind it through a 200-mesh sieve. Wash with deionized water until the pH of the filtrate is >6, put the product in a drying oven at 80°C and dry for 12 hours to obtain the activated carbon material.

The prepared activated carbon is used to make electrodes according to the method of Example 1, and assembled into an electric double layer capacitor, and its specific capacity reaches 140 F/g.

Claims (9)

1. a kind of gac material is characterized in that it is to be carbon source with moso bamboo, adopts phosphoric acid-carbon dioxide physicochemical activation method to prepare, and its preparation method specifically comprises the steps: (1) Take the moso bamboo slices, add phosphoric acid solution to fully soak them, take out the moso bamboo slices and dry them; (2) Place the moso bamboo slices obtained in step (1) in a tube furnace, raise the temperature to 400-800°C under the protection of _N2 atmosphere, then switch to _CO2 atmosphere for constant temperature activation for 1-4h, and switch back to _N2 after the end Protected and cooled to room temperature; (3) Grinding and sieving the product obtained in step (2), washing with deionized water until the pH value of the filtrate is greater than 6, and drying to obtain an activated carbon material. 2. The activated carbon material according to claim 2, characterized in that: in the step (1), the mass ratio of phosphoric acid to bamboo chips is 2-4:1. 3. The activated carbon material according to claim 1 or 2, characterized in that: the mass fraction of the phosphoric acid solution is 40-85%. 4. The activated carbon material according to claim 1 or 2, characterized in that the soaking in step (1) is carried out at room temperature, and the soaking time is 1-9 days. 5. The activated carbon material according to claim 3, characterized in that: the soaking in step (1) is carried out at room temperature, and the soaking time is 1 to 9 days. 6. The activated carbon material according to claim 1, characterized in that: in the step (2), the moso bamboo slices are placed in a tube furnace, and the temperature is raised at a heating rate of 5-10°C/min under the protection of _N2 atmosphere to 400~800°C. 7. The activated carbon material according to claim 1, 5 or 6, characterized in that: in the step (2), the moso bamboo slices are placed in a tube furnace, and the temperature is raised to 500~600°C under the protection of _N2 atmosphere , and then switch to CO ₂ atmosphere for constant temperature activation for 3-4h. 8. The activated carbon material according to claim 7, characterized in that: in the step (2), put the moso bamboo slices in a tube furnace, raise the temperature to 500°C under the protection of N ₂ atmosphere, and then switch to CO ₂ The atmosphere was activated at constant temperature for 3h. 9. the application of activated carbon material according to claim 1 as electrode material of electric double layer capacitor.

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