Double layer high power capacitor comprising a liquid...

Details Double layer high power capacitor comprising a liquid... Double layer high power capacitor comprising a liquid...

2000-01-18

2003-12-30

Reichard, Dean A. (Department: 2831)

Electricity: electrical systems and devices

Electrolytic systems or devices

Liquid electrolytic capacitor

C361S502000, C361S503000, C361S508000, C361S516000, C029S025030

Reexamination Certificate

active

06671166

ABSTRACT:

The invention relates to supercapacitors, or high-capacitance capacitors, comprising an electrolyte consisting of an organic solution of a salt.
A supercapacitor is a component intermediate between a capacitor and a battery in terms of energy and power. A battery delivers a great deal of energy (40 to 150 Wh/kg) but this component is limited in terms of power (<5×10
2
W/kg). A capacitor delivers a high pulse power (10
4
to 10
6
W/kg) but its associated energy per unit mass is low (<0.1 Wh/kg). The term “supercapacitor” should be understood to mean any electrochemical system using at least the surface properties of an ideally polarizable material of high specific surface area. In other words, the super-capacitor is an electrochemical capacitor of high capacitance.
The origin of the operation of a supercapacitor is based on the principle of the double layer. During charging of the supercapacitor, there is a build-up of ionic species on either side of the two electrodes, at the ideally polarizable material/electrolyte interface. There may also be oxidation-reduction reactions in the presence of redox sites, resulting in a pseudocapacitive system.
Supercapacitors based on the principle of the double layer have been manufactured from a variety of materials. These supercapacitors are assembled from two carbon electrodes having a high specific surface area.
In general, the capacitors furthermore include current leads, a separator lying between the electrodes, an electrolyte and a package sealed with respect to the environment.
One of the key components of a supercapacitor consists of the electrolyte which, typically, comprises a solution of a salt, that is to say a combination of a salt and a solvent.
In general, the electrolytes are low-viscosity liquids and have a high conductivity over a wide temperature range. They must also be of low cost, chemically and electrochemically stable and compatible with carbon or the other materials of which the electrodes are composed.
Many liquid electrolytes intended to meet these requirements have already been proposed.
Patent Application EP-A-704,871 describes an electrolyte consisting of an organic solution of a quaternary ammonium salt. Examples 1 and 2 mention particularly a &ggr;-butyrolactone solution containing 20% monotetramethylammonium phthalate or a &ggr;-butyrolactone solution containing 20% triethylmethylammonium maleic acid.
Patent Application EP-A-694,935 describes a solution in a nitrile solvent of a salt consisting of an ammonium cation and of anions chosen especially from trifluoromethyl sulfonate, bistrifluoromethyl sulfonyl imide, trifluoromethylsulfonyl carbanion, tetrafluoroborate, hexafluorophosphate, hexafluoroarsenate, perchlorate. This document mentions in particular tetraalkylammonium tetrafluoroborate.
U.S. Pat. No. 5,450,279 describes a solution of tetraethylammonium tetrafluoroborate or tetraethylammonium perchlorate in an organic solvent such as propylene carbonate or &ggr;-butyrolactone.
U.S. Pat. No. 4,562,511 describes a double-layer supercapacitor formed from two electrodes separated by a separator impregnated with an electrolyte. Each electrode consists of a polarizable carbon layer and of a conductive layer. The electrolyte is a solution of &ggr;-butyrolactone or propylene carbonate and tetraethylammonium perchlorate.
Patent Application EP-A-660,346 describes a double-layer supercapacitor in which the electrolyte is an organic solution of a lithium or ammonium salt. Especially mentioned as solvents are ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, &ggr;-butyrolactone, acetonitrile and 1,2-dimethoxyethane and especially mentioned as salts are the lithium salts LiAsF
6
, LiBF
4
, LiPF
6
and LiClO
4
, or ammonium salts.
The document Chemical Abstract, Vol. 106, No. 10 describes an electrolyte based on propylene carbonate and on a tetrafluoroborate enclosed in a crown ether, probably in order to improve the solubility of the tetrafluoroborate.
Patent Abstracts of Japan, Vol. 017, No. 249 describes an electrolyte formed from a quaternary ammonium salt of tetrafluoroboric acid in solution in &thgr;-butyrolactone, optionally as a mixture with acetonitrile or nitromethane.
Patent Abstracts of Japan, Vol. 014, No. 573 describes an electrolyte formed from phosphonium and ammonium salts in solution in propylene carbonate.
Many other supercapacitors have been described which make use of other organic solutions, for example potassium-based organic solutions, such as document WO-A-94/28563.
Nevertheless, there is a need to provide improved electrolytic systems which give optimum capacitance in order to produce high-power supercapacitors while still allowing low-cost mass production.
Surprisingly, the inventors have found that it is possible to use, advantageously, an electrolyte consisting of an organic solution of a salt whose cation is the sodium or potassium cation, or the cation of an alkaline-earth metal chosen from magnesium or calcium, in a solvent comprising one or more amides.
The invention therefore relates to an ideally polarizable supercapacitor consisting of a positive electrode and its current collector, a negative electrode and its current collector, said electrodes comprising a carbon material having a high specific surface area, of a separator and of a nonaqueous liquid electrolyte impregnating said separator and said electrodes, characterized in that the nonaqueous liquid electrolyte is an organic solution of a sodium or potassium salt or an alkaline-earth metal salt, said salts being present by themselves or as a mixture in a solvent comprising one or more amides.
The required properties for a carbon material that can be used as electrodes are a high specific surface area per unit weight, a low electrical resistance and good electrochemical stability.
The carbon materials may be in the form of powders or fibers and are obtained, for example, from petroleum pitch, phenolic resin, coconut shells and other equivalent products. Such carbon materials are, for example, described in documents U.S. Pat. No. 4,562,511 or U.S. Pat. No. 5,450,279.
The electrode is based on a carbon material, for example an active carbon having a specific surface area of between 300 and 3000 m
2
/g, preferably greater than 1000 m
2
/g.
According to an advantageous variant, each electrode is formed from a porous composite film of a polymeric material having a high specific surface area, especially greater than 10 m
2
/g, filled with a carbon material, especially active carbon, and preferably greater than 20 m
2
/g.
The polymeric material is formed from thermoplastic elastomers or polymers which are insoluble in the aqueous and/or organic solvents and which ensure cohesion of the product (structural polymers or elastomers) and from thermoplastic polymers or elastomers having polar groups which remain in the film after the manufacturing process that results in said porous film has been carried out.
Among insoluble elastomers or polymers, mention may especially be made of polyolefins such as polypropylenes, polyethylenes and ethylene-propylene copolymers. These polyolefins are such that they can be produced in the form of film and are well known especially as packaging films. They may include, for example, be low-density or high-density polyethylene optionally comprising as copolymer a greater or lesser amount of an alpha-olefin.
They may also include polyamides, such as polyether-block-polyamides, polyimides, vinyl copolymers carrying a high ethylene monomer content, such as polyethylene vinyl acetate having a high ethylene monomer content, acrylic polymers, aromatic polymers like the polystyrenes, such as polystyrene-butadiene copolymer, fluorinated polymers such as polyvinylidene fluoride, copolymers formed from the monomers belonging to one of the abovementioned families, for example vinylidene fluoride-hexafluoropropylene copolymers and vinylidene fluoride-trifluoroethylene copolymers.
Preferably, the thermoplastic elastomers or polymers insoluble in the solvents are chosen from th

Affiliated with

Also associated with

Rating

Double layer high power capacitor comprising a liquid... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Double layer high power capacitor comprising a liquid..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Double layer high power capacitor comprising a liquid... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3117970