JP2014513423A - Carbon electrode and electrochemical capacitor - Google Patents

Abstract

  Carbon electrodes for capacitors having carbon elements treated in combination with a high concentration electrolyte tetrafluoroborate and a non-water soluble aprotic solvent to provide an operating voltage of up to 4.5V and these Capacitor used with other carbon electrodes.

Description

  The present invention relates to conditioned carbon for electrodes and electrochemical capacitors comprising these electrodes. More specifically, the water-insoluble non-acetonitrile electrolyte (non-acetate electrolyte) having a high concentration of electrolyte salt in which the capacitor is treated carbon for the electrode of the present invention is quaternary tetrafluoroborate salt. A synergistic improvement is provided when used in combination with an aquaous non-acetontrilile electrolyte.

Activated carbon is a suitable material used when manufacturing the electrode of a carbon electrode capacitor. This activated carbon is made from several different raw materials such as coconut shell, wood, sugar, cellulosic material, and phenolic resin. After converting these materials to carbon under steam controlled conditions, the carbon is “activated” in a second step using steam, or catalyzed by KOH or by carbon dioxide and KOH. To increase the surface area to a very large surface area such as 1000-2400 m ² / g. These activated carbons usually contain about 2% oxygen and trace amounts of inorganic salts after complete drying. This oxygen is probably present as quinone, hydroquinone, phenol, carboxylic acid, furan, and possibly ketone, along with some nitrogen compounds, all of which are relatively high voltage conditions above 3V. Below, as the voltage increases beyond 3.3V, it will undergo electrochemical oxidation / reduction. At relatively low voltages, these functional groups actually improve the energy storage capacity of carbon and are desirable at voltages below 3.2V. However, as the voltage increases above 3.2V, high leakage current with gas formation, increased ESR (resistance value), and loss of performance occur.

  Electrochemical double layer capacitors called “super-capacitors” with the ability of high energy density are assembled from various materials. In general, as described in U.S. Patent No. 6,057,049 issued to Kaschmitter et al., It is desirable that supercapacitors be constructed with lightweight materials and electrolytes that are stable and non-reactive. The contents are hereby incorporated by reference. This type of supercapacitor incorporates an electrode based on carbon, which may be made from an organic gel.

  U.S. Patent No. 5,677,027 to Smith et al. Relates to a complex salt electrolyte formed by mixing a tetraalkylammonium salt of hydrogen fluoride and an imidazolium compound in a nitrile solvent that functions at temperatures of -60 to 150C. The contents of the literature are hereby incorporated by reference.

  Non-Patent Document 1 discloses a high dielectric constant solvent and an onium salt for a double layer capacitor, the contents of which are incorporated herein by reference. Specifically, quaternary onium tetrafluoroborate salts that exhibit relatively high solubility in solvents with good stability and conductivity have been studied.

  U.S. Pat. No. 6,057,038 to Warren et al. Discloses a method for producing tetraalkylammonium tetrafluoroborate used as an electrolyte with a dinitrile mixture as a solvent, the content of which is Incorporated herein by reference.

  U.S. Patent Nos. 5,057,069 and 5,037, Smith, et al. Disclose similar electrolytes primarily utilizing nitrile solvents, the contents of which are also incorporated herein by reference.

US Pat. No. 5,260,855 US Pat. No. 6,902,683 US Pat. No. 5,418,562 US Pat. No. 6,535,373 US Pat. No. 6,902,684

Ue, “Electrochemical Properties of Organic Liquid Electrodes Based on Quarterly Onion Salts for Electric 11th Month, 11th.

  In accordance with one embodiment of the present invention, improved carbon electrodes for relatively high voltage electrochemical double layer capacitors (EDLCs) and methods for their manufacture are provided.

  The carbon electrode is manufactured as a disc formed from carbon particles heat treated at 850 ° C. to 1300 ° C., preferably about 1050 ° C. to 1190 ° C. for about 30 to 60 minutes in an inert atmosphere or vacuum. . This carbon was formed into 4 mm sheets with Kynar® binder and then cut into electrode disks. The increment applied to the disk in the capacitor test cell is then held for 3 cycles in each step under an inert atmosphere by using a voltage ramp of 2 to 4.4 volts with an increment of 0.5 volts. These electrodes were tested.

  According to another feature of the invention, the electrolyte of the EDLC comprises an aprotic, non-aqueous, non-acetonitrile solvent and at least one relatively high concentration (2.0- 4.0M: 20-55% by weight) tetraalkylammonium tetrafluoroborate salt.

  Advantageously, an aluminum metal collector is used with the capacitor electrode.

  It is a general object of the present invention to provide an EDLC having an operating voltage of up to 4.0-4.5V.

  According to one aspect of the present invention, the treated activated carbon particles are formed as a sheet, which is then cut into a disk for an electrode having a metal collector, wherein the carbon is A second conductive carbon layer is disposed on the upper and lower surfaces of the heat-treated carbon layer, and a porous inert separator is interposed between the conductive carbon layers. Existing.

  It is a general object of the present invention to produce a carbon electrode for a capacitor that includes a disc composed of post-treated activated carbon particles that do not contain ash, silica, or compounds having oxygen or sulfur functional groups. .

  It is another object of the present invention to provide a capacitor having a carbon electrode that operates at a relatively high voltage (above 3.0 to 4.5V).

  The present invention may be more fully understood with reference to the preferred embodiments of the invention and the drawings.

It is a front view of the carbon disk for electrochemical double layer capacitor electrodes of the present invention. It is sectional drawing of the electrode which has a disc of FIG. It is sectional drawing of another electrode of this invention. FIG. 4 is an exploded view of the electrode of FIG. 3.

In accordance with the present invention, an improved electrochemical carbon electrode double layer capacitor (EDLC) is provided, which is a water-insoluble non-acetonitrile electrolyte and at least one conductivity of the formula RR ₁ R ₂ R ₃ NBF _4. Having an electrochemically stable carbon electrode with an electrolyte having a conductivity of about 20-30 mS / cm at 25 ° C. with a conductive ammonium salt and increasing to 65 mS / cm at about 80 ° C. , R, R ₁ , R ₂ , and R ₃ are ethyl or methyl groups, or R, R ₁ , R ₂ , and R ₃ are ethylene carbonate, propylene carbonate, gamma butyrolactone, dimethyl carbonate, or these One or two pyrrolidinyl groups at a concentration of 2.0 to 4.0 M in a solvent selected from the group consisting of a mixture That. The carbon of the electrode is activated carbon formed as a disc after being heated at 850 ° C. to 1300 ° C. for about 30 to 60 minutes in an inert atmosphere. Preferably, the carbon has been previously acid washed to remove ash. Capacitors with discs are tested at a constant voltage of 3.5V to 4.5V.

Suitable ammonium salts have a molecular weight in the range of 175-250. Further preferred salts are diethyldimethylammonium tetrafluoroborate (DEDMA BF ₄ ) and ethylmethylpyrrolidinyl tetrafluoroborate. A suitable solvent is a combination of ethylene carbonate (EC) and gamma butyrolactone (GBL) or propylene carbonate (PC) or dimethyl carbonate (DMC), with GBL, PC, DMC, Or the ratio of these mixtures is 70%.

  The electrode used in the capacitor is acid-washed activated carbon used in the electrode, and then in an inert atmosphere or vacuum at 850 ° C. to 1300 ° C., preferably 1000 to 1300 ° C. for about 30 to 60 minutes. Heat treatment, forming a carbon disk for the electrode, and then subjecting the capacitor with the electrode to constant voltage cycling in the range of 3.5-5V.

  As shown in FIGS. 1 and 2, the electrode (10) of the present invention has an aluminum metal foil collector (11) having a thickness of about 1-4 mils at the top and bottom. On these collectors (11) is an optional conductive carbon coating (12) with a thickness of about 0.5-1 mil. On these coatings (12) there is a disc (13) with treated relatively large surface area conductive carbon having a binder thickness of about 2-5 mils. Between these conductive carbons (13), a conventional porous insulating separator (14) having a thickness of about 0.5 to 3 mils is used. The coating (12) may have the same treated carbon as found in the layer (13).

  Separator (14) can have any conventional inert separator used in making carbon electrodes. A preferred separator is porous Teflon®. The electrode used may be symmetric or asymmetric.

  A disc having a conductive carbon layer (13) is obtained in combination with an inert polymer binder such as polytetrafluoroethane, Surlyn® or Kynar® present in an amount of about 6% by weight. Having pretreated conductive carbon produced according to the invention.

  The disc layer (13) is a mixture of about 0.02 grams of treated carbon with about 6% polytetrafluoroethane or Kynar® in acetone solvent and the mixture is rolled back and forth under pressure. It can be manufactured by forming a 5/8 ″ circular layer having a thickness of about 2-5 mils by punching and vacuum drying. The particle size of the carbon particles is about 0.5 to 10 microns. The discs can also have different shapes, i.e. squares, rectangles, circles, etc.

  Alternatively, the activated carbon can be used to form carbon particles used to form the electrode disk (13) after grinding with an acid ball mill to about 0.5-10 microns, preferably 3-6 microns. Produced by treating and then removing oxygen and sulfur functional groups by heat treatment in an oven at 850-1300 ° C., preferably at 1100 ° C., followed by washing and drying under vacuum be able to. The heat treatment step is performed in an inert atmosphere.

  Then, after the post-treated activated carbon is formed as a disc (13), it is placed in a capacitor test cell in a state where constant voltage cycling of 2 to 4.1 V is imposed on the electrolyte.

  The capacitor is provided with means for degassing the carbon disk within the electrode to remove the gas formed during initial voltage cycling (less than 10 cycles).

Aluminum collector The aluminum collector used in the electrode is preferably from a simple annealed aluminum foil with a coating of a water based conductive carbon acrylic coating, such as the commercially available Acheson carbon acrylic conductive coating. Manufactured and later fired at 200 ° C. Burn-in and degassed aluminum is suitable for the anode or cathode.

  The post-treated activated carbon may be prepared by Kynar® and coated directly on the aluminum collector foil as a 3-6 mm thick electrode layer. This may be on one side or on both sides.

Suitable electrolytes Suitable solvents have a combination of ethylene carbonate (EC) and one or more of the group consisting of gamma butyrolactone (GBL), propylene carbonate, or dimethyl carbonate, in this case The ethylene carbonate has at least 20% by weight, preferably 40-60% by weight.

  The salt concentration is at least 1.0M, preferably 1.5 to 5.2M, and most preferably 1.5 to 3.5M. Mixtures with spiro or bis-pyrrolidinyl ammonium tetrafluoroborate also provide good low temperature efficiency.

  These improvements are observed relatively prominently in these electrolytes when the ionic salt content exceeds 2.5-4.0M and is twice that of current electrolytes, resulting in conductivity. Better charge / discharge capacitance efficiencies are obtained than those obtained from the rate value alone.

  It turns out that ethylene carbonate (EC) is essential to achieve a significant improvement in electrical conductivity compared to current aprotic non-acetonitrile electrolytes (18-19 mS / cm) based solely on propylene carbonate (PC) did.

Example 1
Manufacture of electrodes 1 and 2, forming an acetone slurry of 10% Kynar® resin and 90% carbon (0.5-10 microns) treated to remove ash and silica. The carbon electrode manufactured by can be observed. Spread the mixture on a flat Teflon® sheet and then allow the acetone to evaporate. The dried sheet is removed from the Teflon® and punched into 5/8 ″ circular electrodes and vacuum dried. The weight of the electrode is about 0.01 grams and the thickness is 4 mils.

  B. Alternatively, the carbon electrode (20) can be formed by removing the end plate (21) from a sheet of aluminum covered by a thin liquid conductive carbon dispersion, as shown in FIGS. It can also be fired after being manufactured. From this sheet, one dry and properly sized disc (21) is punched and placed on a roller to flatten the edges. The Surlyn® ring (23) is then heat sealed to the end plate (21). The heat treated carbon is then pasted with 10% Surlyn® binder and acetone. This paste is formed by a roller into a sheet of about 4 mm with a Teflon® sheeting. After the acetone has evaporated, it is adjusted by punching to a size that fits within the Surlyn® ring. The carbon electrode (24) is then fired under vacuum to remove all moisture. The separator (22) is a 0.5 mil thick porous Teflon® disk, which is slightly smaller than the end plate (21) but smaller than the electrode (24). large. Prior to assembly, the electrode (24) is immersed in a suitable electrolyte and then placed in a Surlyn® ring. Center the separator on one Surlyn® ring assembly. The other Surlyn® ring assembly is then placed on top of the other assembly and the entire assembly is heat sealed together.

Example 2
Comparison of capacitor test cells with electrolyte of DEDMABF4 in EC / GBL using post-treated OSAKA PC carbon electrode (0.008 g)

  As a result of the relatively high molarity, an improvement in energy has been brought about.

Example 2
Comparison of capacitor test cells with DEDMABF4 electrolyte in 50/50 EC / PC using post-treated Norit 30 carbon (0.008 g)

  As a result of the relatively high molarity, an improvement in energy has been brought about.

Claims (13)

An improvement with at least one carbon electrode in a water-insoluble electrochemical capacitor having a sealed carbon electrode, comprising:
a) metal collectors on the upper and lower surfaces;
b) an optional first conductive carbon layer on each of the upper and lower inner surfaces of the collector;
c) A porous second conductive carbon layer on each of the first conductive carbon layers, substantially free of oxygen and heteroatoms containing functional groups And a degassed second conductive carbon layer;
d) a porous inert separator between the second conductive carbon layers;
e) an electrolyte having a quaternary ammonium tetrafluoroborate concentration of at least 1.5M in an aprotic solvent;
Having an improvement.   The capacitor of claim 1 having a non-acetonitrile electrolyte.   The capacitor according to claim 2, wherein the electrolyte includes an aprotic solvent and at least one tetraalkylammonium tetrafluoroborate.   The capacitor according to claim 3, wherein the salt concentration is 2.0 to 4.8M.   The capacitor of claim 1 having an aluminum metal collector.   The capacitor according to claim 2, wherein the electrolyte solvent includes two selected from the group consisting of ethylene carbonate, propylene carbonate, gamma butyrolactone, and dimethyl carbonate.   An improvement in a capacitor having a carbon electrode, wherein the carbon in the electrode is heat treated to remove oxygen and sulfur functional groups and silica by heating at a temperature of 850 to 1300 ° C. to form at least one disc. An improvement is formed and the disc is used in the electrode, the electrode being placed in the capacitor and undergoing burn-in and degassing with an upward ramp of voltage to 4.4. The electrolyte for the electrode has a conductive tetraammonium salt of the formula R, R ₁ , R ₂ , R ₃ , NBF ₄ , where R, R ₁ , R ₂ , R ₃ are ethyl or methyl The capacitor according to claim 7, wherein R, R ₁ , R ₂ , and R ₃ are one or two pyrrolidinyl groups in an aprotic solvent.   The capacitor according to claim 7, wherein the electrolyte solvent is at least two members selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, and gamma butyrolactone.   The capacitor of claim 7, wherein the salt concentration is about 1.5 to 4.8M.   The capacitor of claim 7, wherein the electrolyte solvent comprises about 40-60% ethylene carbonate.   The capacitor of claim 7 having an annealed aluminum collector.   The capacitor of claim 7, wherein the carbon in the electrode is acid cleaned prior to heat treatment to remove ash and salt.

Images