METHOD FOR PRODUCING MICROPOROUS CARBON MATERIAL

Abstract

Processes for the production of microporous carbon material, for use in electrodes of supercapacitors and secondary batteries, in which particulate metal carbide material is fluidized with a halogen gas at a high temperature in a fluidized bed reactor, the halogen gas is desorbed at a lower temperature of 150? C. to at most 250? C. under vacuum, and then the material is passivated using hydrogen gas and then milled.

Claims

1.-11. (canceled)

12. A method for manufacturing microporous carbon material, the method comprising the steps of: a) in a fluidized bed reactor, fluidizing a granular metal carbide material with a halogen gas or a gas mixture containing a halogen gas at a temperature of including 800? C. up to and including 1300? C.; b) maintaining a product obtained from step a) at a temperature of including 150? C. to at most 250? C. and under vacuum at a pressure of including 1 mbar to including 300 mbar; and thereafter or subsequently c) maintaining the product under an atmosphere of a hydrogen gas or a gas mixture containing at least 30% by volume of hydrogen based on a total volume of the gas mixture at a temperature of including 800? C. up to and including 1300? C.; and d) comminuting the product to a D90 particle size of including 10 ?m to including 30 ?m and a D10 particle size of including 1.5 ?m to 2 ?m.

13. The method of claim 12, wherein step a) comprises, after fluidizing with the halogen gas or gas mixture, fluidizing with a purge gas in the fluidized bed reactor at a temperature of including 800? C. to including 1300? C., wherein the purge gas does not react with at least carbon at said temperature.

14. The method of claim 13, wherein the purge gas is selected from a group consisting of: helium, neon, argon, krypton, and xenon.

15. The method of claim 13, wherein the purge gas is argon.

16. The method of claim 12, wherein the granular metal carbide material is selected from a group consisting of: vanadium carbide material, titanium carbide material, molybdenum carbide material, silicon carbide material, tungsten carbide material, tantalum carbide material, and niobium carbide material.

17. The method of claim 12, wherein the granular metal carbide material is silicon carbide material and wherein the halogen gas is chlorine.

18. The method of claim 12, wherein in step a) the halogen gas is supplied in an amount which is from both including 100% to including 110% of the stoichiometrically required amount.

19. The method according to claim 12, wherein in step b) the pressure is from including 5 mbar to including 200 mbar, or from including 5 mbar to including 80 mbar, or preferably from including 8 mbar to 15 mbar.

20. The method according to claim 12, wherein: step a) is carried out for a duration of from including 8 hours to including 13 hours; step b) is performed for a duration of from including 12 hours to including 30 hours; and step c) is performed for a duration of from including 2 hours to including 4 hours.

21. The method of claim 20, wherein: in step a) fluidizing with halogen gas is performed for a duration of including 9 hours up to and including 11 hours, and fluidizing with a purge gas is performed for a duration of 1.5 hours up to 2.5 hours; and step b) is carried out for a duration of from including 22 hours to including 26 hours.

22. The method according to claim 12, wherein step c) is carried out before step d), or wherein step d) is carried out before step c), or wherein step c) is carried out before step d) and then step c) is carried out again for a shorter duration.

23. The method according to claim 12, wherein step b) is carried out using the fluidized bed reactor.

24. The method according to claim 12, wherein step c) is carried out using the fluidized bed reactor or using a rotary kiln.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Examples of embodiments are explained in more detail with reference to the accompanying schematic drawings. Therein:

[0054] FIG. 1 depicts a schematic flow diagram of the manufacturing process;

[0055] FIG. 2 depicts a scanning electron micrograph of a particle cross-section after synthesis and before size reduction; and FIG. 3 depicts a diagram of the pore size distribution of the material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0056] Reference is made in the following to FIG. 1, which shows an embodiment of a method for manufacturing microporous carbon material.

[0057] The method comprises a treatment step S100. In the treatment step S100, particulate metal carbide material, for example silicon carbide, is initially fed into a fluidized bed reactor. The reactor and thus the metal carbide material are heated to a temperature of about 1000? C. Lower temperatures from 800? C. are also conceivable. The heating process preferably takes between 1 hour and 1.5 hours.

[0058] Then the metal carbide material is fluidized by means of a halogen gas, preferably chlorine gas. The volumetric flow rate of the chlorine gas is adjusted so that about 100 percent to 110 percent of the stoichiometrically required amount of chlorine gas flows through the fluidized bed reactor.

[0059] Fluidization at high temperature is carried out for a period of about 2.5 hours to 3.5 hours per kilogram of metal carbide material in the fluidized bed reactor.

[0060] After completion of the halogen treatment, the fluidized bed reactor is fluidized with a purge gas at a constant high temperature. The purge gas is such that it does not react with the carbon even at the high temperatures of 1000? C. The preferred purge gas is, for example, argon. The purge gas may also be a mixture of multiple substances.

[0061] The method further comprises a desorption step S102. In the desorption step, the product obtained from the previous step is removed from the fluidized bed reactor and kept at a temperature of preferably 195? C. to 205? C. under a rough vacuum of about 10 mbar. During this process, excess halogen gas escapes from the material. The halogen gas dissolving from the material can visibly set the powdered material in motion.

[0062] Preferably, the desorption step S102 is carried out at least until the visible movement of the material comes to a standstill. A small safety period of about 15 min to 30 min can still be provided for the desorption step S102 by which the step is carried out longer. The desorption step can also be carried out without separate monitoring. In this case, the desorption step S102 is carried out for, for example, 12 hours to 24 hours.

[0063] The method further comprises a passivation step S104 and a grinding step S106. These steps are performed after the treatment step S100 and the desorption step S102.

[0064] For the passivation step S104, the material obtained from the previous steps is charged into a rotary kiln or into a fluidized bed reactor. The material is heated to a temperature of about 1000? C. and brought into contact with hydrogen gas or a gas mixture containing at least 50 percent by volume of hydrogen based on the total volume of the gas mixture. In the case of the fluidized bed reactor, the material is fluidized with the hydrogen gas or the gas mixture.

[0065] The duration of the passivation step is preferably based on the total dissolved solids (TDS) value of the passivated material. To determine the TDS value, the carbon is boiled in distilled water for 10 min and the filtered-off water is measured at 25? C. using a conductivity probe. The passivation step S104 is carried out at least until the TDS value reaches or falls below 50 ?S/cm. This is because in this case the risk of damage to the electrodes due to corrosion by the slurry increases. The passivation step S104 is preferably carried out until the TDS value is between 2.5 ?S/cm and 50 ?S/cm, preferably up to 10 ?S/cm, more preferably up to 5 ?S/cm.

[0066] Then, in comminution step S106, the passivated material is comminuted to a particle size D90 of inclusive 10 ?m to inclusive 15 ?m and a particle size D10 of more than 1.5 ?m to 2 ?m. These particle sizes allow the formation of a slurry which is particularly suitable for further processing for the production of supercapacitors and secondary batteries or their electrodes.

[0067] The comminution step S106 can be carried out before or after the passivation step S104. If the comminution step S106 is performed after the passivation step S104, it is advantageous to perform the passivation step S104 again, but for a shorter duration than the first pass.

Example 1: Carbon Material Made from SiC

[0068] Reference is made in the following to FIGS. 2 and 3, which show characteristic features of the microporous carbon material obtained by the previously explained method based on SiC.

[0069] FIG. 2 shows a scanning electron microscope image of a section through a single particle prepared according to the present invention. There are clearly macropores present in the material.

[0070] As can be seen from FIG. 3, the carbon material has a high number of pores with a pore diameter between 5 angstroms (?) and 9 ?. The most common pore size is about 6.5 ?.

[0071] In addition to these micropores, the material also has micropores with a pore diameter of more than 9 ? to almost 20 ?. The most common in this range is a pore diameter of about 11.5 ? to 12.5 ?. It has been shown that such a pore distribution, including the macropores, is particularly suitable for the fabrication of supercapacitors and secondary batteries.

[0072] The porosity was determined by nitrogen physisorption in conjunction with the Brunauer-Emmet-Teller (BET) and Rouquerol evaluation methods as described in the IUPAC Technical Report: Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution (IUPAC Technical Re-port) by Thommes et al, Pure Appl. Chem. Chem. 2015; 87(9-10): 1051-1069. This disclosure is specifically incorporated herein by reference. The total pore volume was determined using BET, while the micropore volume was determined using density functional theory (DFT). Since not all assumptions of the BET method may be met for microporous materials, the surface areas determined from the BET method and the DFT method may appear contradictory. A look at the pore size distribution allows the correct estimation of the ratio of the surfaces to each other, i.e. how much surface area of the carbon material is due to micropores.

[0073] The microporous carbon material produced from SiC using the method presented here had a surface area of about 1290 m.sup.2/g and a total pore volume of 0.6 cm.sup.3/g. The total pore volume is determined at a relative pressure of 0.95 according to IUPAC. Here, the micropore volume accounts for about 0.5 cm.sup.3/g and the micropore surface area is about 1334 m2/g. Considering the pore size distribution in FIG. 3, it can be concluded that almost the entire surface area is due to micropores, with the majority of the micropores again having diameters of 5 ? and 9 ?.

[0074] In addition, the microporous carbon material produced by this method has an ash content of less than 1% by weight based on the total mass of the microporous carbon material. The skeletal density is about 2.277 g/cm.sup.3 to 2.451 g/cm.sup.3. The skeletal density was determined by helium pycnometry at constant volume (Used gas pycnometer AccuPyc II from Micromeritics).

[0075] Using standard spectroscopy techniques, the carbon material was shown to contain graphitic and also amorphous structures (Ramanspectroscopy), as well as being free of oxygen-containing groups on the surface (IR spectroscopy).

Example 2: Carbon Material Made from TiC

[0076] The method as previously described is performed with TiC as tha carbide material. The pore size distribution is similar to SiC, but the primary peak is at 8.5 ?. The carbon material has a surface area of about 1681 m.sup.2/g and a total pore volume of 0.8 cm.sup.3/g. Of this, the micropore volume accounts for 0.6 cm.sup.3/g and the micropore surface area is about 1448 m.sup.2/g.

Comparative Example: Commercially Available Activated Carbon

[0077] Commercially available activated carbon is available, for example, under the trade name YP-50F from Kuraray. The primary peak of the pore size is at 8 ?. The carbon has a surface area of about 1707 m.sup.2/g and a total pore volume of 0.9 cm.sup.3/g. The micropore volume accounts for 0.6 cm.sup.3/g and the micropore surface area is 1289 m.sup.2/g.

[0078] In order to improve the production of microporous carbon material, especially for use in electrodes of supercapacitors and secondary batteries, a method is proposed in which particulate metal carbide material is fluidized with a halogen gas at a high temperature in a fluidized bed reactor, the halogen gas is desorbed at a lower temperature of 150? C. to at most 250? C. under vacuum, and then the material is passivated using hydrogen gas and then milled.

[0079] While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms comprise or comprising do not exclude other elements or steps, the terms a or one do not exclude a plural number, and the term or means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.