Method for purifying active carbon-based material of super-capacitor electrode
Technical Field
The invention relates to the field of electrode materials of a super capacitor, in particular to a method for purifying an active carbon-based material of a super capacitor electrode.
Background
Super-capacitor type energy storage devices based on ion adsorption/desorption, such as electric double layer capacitors, battery capacitors and the like, usually use porous carbon-based materials as main or partial electrode active components and tetraethylammonium tetrafluoroborate (TEA-BF) 4 ) Triethylmethylammonium tetrafluoroborate (TEMA-BF) 4 ) Bispyrrolidine spiro quaternary ammonium salt (SBP-BF) 4 ) Lithium hexafluorophosphate (LiPF) 6 ) The electrolyte is dissolved in an aprotic solvent such as acetonitrile or carbonate as an electrolytic solution. Porous carbon-based materials, including activated carbon, microporous carbon, mesoporous carbon, carbon nanotubes, graphene and composite and mixed materials thereof, are one of the most critical factors for determining super capacitive energy storage performance, and have ultralow metal impurity content and high specific surface (difficult to wet) (C)>1500m 2 A/g) and a porous (0.1-50 nm) structure. The metal and non-metal impurities of the porous carbon-based material have obvious influence on super capacitive energy storage using the non-protonized solvent electrolyte, so that not only is the leakage current and the equivalent resistance increased, but also side reactions such as electrolyte decomposition are catalyzed and initiated, and the generated gas can cause the risk of expansion or deformation, burst and the like of a device. This also shortens the life of the super capacitor type energy storage device, especially the charge and discharge cycle stability and life at high voltage or high temperature.
The metal and non-metal impurities in the active carbon-based material of the super capacitor electrode mainly originate from two aspects: inherent raw materials, such as natural products like coconut shells serving as an activated carbon source, and metal and nonmetal impurities contained in coal, petroleum coke and the like; introduction during preparation, e.g. KOH, znCl 2 Activated carbon activators, carbon nanotube growth catalysts such as Fe, co and Ni, mgO and Al 2 O 3 、SiO 2 And the like. The common method for removing metal and non-metal impurities in the active carbon-based material of the super-capacitor electrode is dilute acid impregnation and gas phase reaction. Impregnation with dilute acids (e.g., dilute hydrochloric acid, dilute nitric acid, dilute hydrofluoric acid, dilute sulfuric acid, etc.) is usually combined with aeration, pressurization, and addition of chelateThe means such as the mixture promotes the permeation and diffusion of the cleaning liquid into the porous structure and the reaction and dissolution of impurities, thereby improving the cleaning effect. Because the aqueous solution is difficult to effectively permeate, diffuse and wet micropores, tubules, complex irregular surfaces, high aspect ratio structures and hydrophobic substrates, the cleaning process is long and repeated, impurities in pore cavities are difficult to effectively remove, and the deep purification effect is not ideal. Gas phase reactions typically employ gases (e.g., containing Cl) 2 Gas) and can be quickly diffused and fully contacted with the surfaces difficult to be wetted and the pore channel structure, and partial impurities can be removed after being converted into volatile compounds, but not all the impurities can be converted into the volatile compounds, and the types of the impurities capable of being removed are limited.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a method for purifying an active carbon-based material of a super-capacitor electrode. The super capacitor electrode made of the super capacitor electrode active carbon-based material is suitable for an electric double layer capacitor, a battery capacitor and other energy storage devices with super capacitor characteristics, wherein the electric double layer capacitor and the battery capacitor use non-protonized solvents such as acetonitrile and carbonic ester as electrolyte solvents.
Preferably, the method for purifying the supercapacitor electrode active carbon-based material comprises the following steps:
s1, soaking a carbon-based material (a porous carbon material) in an alcoholic solution of hydrochloric acid at normal temperature, wherein the alcoholic solution of hydrochloric acid effectively permeates and diffuses to the surface, the pore ports and the interior of the carbon-based material which are difficult to wet and reacts with impurities to generate an alcohol-soluble byproduct;
s2, filtering and separating the carbon-based material, washing the carbon-based material with deionized water for a plurality of times, and drying to obtain the high-purity carbon-based material with ultralow impurity content.
Preferably, in S1, the hydrochloric acid alcohol solution is an organic solvent in which HCl gas is dissolved.
Preferably, in S1, the organic solvent is one or more of methanol, ethanol, n-propanol, isopropanol, propylene alcohol, ethylene glycol, propylene glycol, and glycerol.
Preferably, in S1, the organic solvent contains 0 to 5% of water.
Preferably, in S1, the concentration of HCl in the hydrochloric acid alcohol solution is 0.001 to 2mol/L.
Preferably, in S1, the alcoholic hydrochloric acid solution contains 0 to 500ppm of HF.
Preferably, in S2, the impurity content in the high-purity carbon-based material is: total ash <0.5%, fe <20ppm, K <10ppm, mn <20ppm, cu <20ppm, na <20ppm, ni <20ppm, cr <20ppm, si <20ppm, ca <10ppm, zn <20ppm, zr <20ppm, al <400ppm.
The beneficial effects of the invention are:
(1) According to the invention, the hydrochloric acid alcohol solution is adopted to replace the traditional dilute acid water solution for impregnation, the hydrochloric acid alcohol solution has low surface tension, can effectively permeate and diffuse to micropores, mesopores, tubules, complex irregular surfaces, high aspect ratio structures and difficult-to-wet substrates in the carbon-based material, is beneficial to full contact of acid and impurities for reaction, and is relatively thorough in impurity removal.
(2) The method for purifying the active carbon-based material of the super-capacitor electrode provided by the invention has the advantages of simple process, short cleaning time and high impurity removal rate.
Drawings
FIG. 1 is a comparison graph of the impurity content of coconut shell activated carbon before and after cleaning with an alcoholic solution of hydrochloric acid;
FIG. 2 is a comparison graph of the impurity content of carbon nanotubes before and after washing with an alcoholic solution of hydrochloric acid.
Detailed Description
The present invention will be further described with reference to the following examples. The following examples are set forth merely to aid in the understanding of the invention. It should be noted that, for a person skilled in the art, several modifications can be made to the invention without departing from the principle of the invention, and these modifications and modifications also fall within the protection scope of the claims of the present invention.
Example 1:
soaking coconut shell activated carbon in hydrochloric acid alcohol solution (HCl concentration is 0.001mol/L, HF content is 100 ppm) for 1hr, filtering to separate coconut shell activated carbon, washing with deionized water for several times, and drying to obtain high-purity coconut shell activated carbon with ultralow impurity content. The change of the impurity content of the coconut shell activated carbon before and after cleaning is shown in figure 1. After cleaning, the main metal impurities and the non-metal Si impurities in the activated carbon material can be effectively removed.
Example 2:
soaking carbon nanotube in hydrochloric acid alcohol solution (HCl concentration of 0.002mol/L and HF content of 100 ppm) for 1hr, filtering to separate carbon nanotube, washing with deionized water for several times, and drying to obtain high purity carbon nanotube with ultralow impurity content. The change in the impurity content of the carbon nanotubes before and after the cleaning is shown in FIG. 2. After cleaning, the main metal impurities in the carbon nanotube material can be effectively removed.
In summary, the invention provides a non-aqueous solution cleaning method, which effectively removes metal and non-metal impurities in the active carbon-based material of the supercapacitor electrode, thereby achieving deep purification.