Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Separator – retainer – spacer or materials for use therewith
Reexamination Certificate
2000-07-07
2001-08-28
Brouillette, Gabrielle (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Separator, retainer, spacer or materials for use therewith
C429S250000, C427S255400
Reexamination Certificate
active
06280880
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for surface treatment of fibrous polyphenylene sulfide or polysulfone. Combined into area structures, such fibers find applications as separators in electrochemical energy storage devices containing alkali electrolyte.
Electrochemical energy storage devices consist of at least one positive and one negative electrode that are surrounded by a liquid electrolyte. To avoid contact between the positive and negative electrode, and thus, to avoid an undesired current flow inside such an energy storage device, the electrodes are isolated from one another by separators without significantly impairing the passage of the electrolyte's ions.
For use as separators, fiber materials must meet the following requirements:
Resistance to electrolyte and oxidation;
Close weight and thickness tolerances;
Mechanical stability (at least a maximum tensile strength of 70 N/5 cm);
Flexibility for a close fit at the electrodes;
Immediate wettability (less than 10 sec) through the Respective electrolyte; and
Temperature resistance up to 80° C.
If the separator fails to meet, or poorly meets, even one of these requirements, significant quality losses or even failure of the electrochemical cell may be the result.
Most often separators of polyamide or polyolefine fibers are employed for the use in storage batteries with an alkaline electrolyte, generally a 30% to 38% aqueous KOH solution.
Generally, untreated, separators of polyphenylene sulfide or polysulfone fibers are poorly wetted by aqueous electrolyte solutions.
From the Patents Abstracts of Japan Vol. 10/No 168 (E-411) Jun. 14th 1986, for Japanese Patent No. JP-A-61-19056, it is known to use area structures of polyolefine, polyvinylalcohol, or polyester that are treated with fluorine-containing nitrogen as separator materials in batteries, especially those with an alkaline electrolyte.
It is also known from the Japanese Patent No. JP-B2-5-46056 to hydrophile synthetic fibers made of polypropylene, polyester or vinylon through a reactive gas of fluorine and oxygen or sulfuric acid. Fibers treated in this manner are used as battery separators that are stable above 45° C.
Fibers or filaments made of polyphenylene sulfide or polysulfone are naturally hydrophobic. With greater wettability through aqueous electrolytes, they would, therefore, be particularly well suited as separator material in electrochemical energy storage devices, because their chemical and thermal resistance makes them resilient to the conditions that occur on the inside of an accumulator.
SUMMARY OF THE INVENTION
It is the principal objective of the present invention to find a way for making polyphenylene sulfide and polysulfone fibers hydrophilic and wettable for alkaline electrolytes such that, immediately after hydrophilization, they exhibit a wetting time of no more than 10 sec against a 30% to 38% aqueous KOH solution. Even after 700 charge and discharge cycles, non-woven separators made of the respective fibers should have a sufficient barrier effect in the battery for it to function properly.
In the following, the term “fibers” relates to both short and long fibers as well as continuous filaments. The terms “non-woven” and “fiber area structures” include high-porosity foils.
A method for surface treatment of a fibrous polyphenylene sulfide or polysulfone was found as a solution to this task, where a gas mixture of 1 to 5% in volume of elemental fluorine, of nitrogen as carrier gas and of no more than 20% in volume elemental oxygen is used, and where this gas mixture is allowed to affect the fibers until the total fluorine content in the fiber material is between 0.01 and 0.2 percent in weight.
Fiber area structures consisting of fibers treated in this manner may be used as separators in batteries with an alkaline electrolyte.
Fluorination can be carried out according to the German Patent No. DE 25 00 598 B2, the disclosure which is incorporated herein by reference. Slight variations of the method are demonstrated in the examples.
Surprising and unforeseeable was that not only the hydrophilic property of the fiber material increased to a multiple of the initial value but that, in addition, a significant increase occurred in the service life and of the cycle strength of the energy storage device.
The drastic degree of increase in service life and cycle strength as well as in the absorption capability for the electrolyte material when using fluorinated polyphenylene sulfide and polysulfone separators according to the invention is demonstrated in the subsequent examples. There, the pretreatment with elemental fluorine is described extensively as well. Fiber and spunbonded materials or fabrics can be used for this purpose.
To accomplish the invention, the nonwovens or fabrics do not need to be altered with regard to their dimensions or porosity that they normally exhibit as separators.
Not only can the pure individual materials be used, but also filament or fiber mixtures of polyphenylene sulfide and polysulfone. These designs are preferred when the area structures are to be exclusively bound thermally; particularly in order to avoid the use of binding agents.
With each of the above-mentioned embodiments of the invention, the necessary requirements for the thermal and mechanical resistance, the flexibility, the wettability and the capillary activity can be fulfilled easily. Fiber area structures, fabrics or spunbonded materials exhibit an absorption capacity of >150 g KOH per m2. The pore volume is above 70%. All area structures resistant are up to 80° C.
REFERENCES:
patent: 4717623 (1988-01-01), Brown et al.
patent: 5002843 (1991-03-01), Cieslak et al.
patent: 2500598 (1975-07-01), None
patent: 6119056 (1986-12-01), None
patent: 546056 (1993-12-01), None
Hoffmann Harald
Schwoebel Rolf-Peter
Brouillette Gabrielle
Carl Freudenberg
Milde Hoffberg & Macklin, LLP
Wills M.
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