Compositions – Electrolytes for electrical devices
Reexamination Certificate
2000-05-23
2002-03-26
Koslow, C. Melissa (Department: 1755)
Compositions
Electrolytes for electrical devices
C359S270000, C359S275000
Reexamination Certificate
active
06361709
ABSTRACT:
The invention relates to an optically transparent polymeric solid electrolyte comprising a polymeric binder, a filler, a conductive salt, an ion-solvating plasticizer and, if desired, further additives and auxiliaries, to a process for the production of solid electrolytes of this type, and to their use in electrochromic systems and displays.
Optically transparent polymeric solid electrolytes are known in principle. They are used, in particular, in electrochromic systems, for example in electrochromic glazing systems, in which the light transparency can be adjusted reversibly and steplessly by application of electrical potentials. The structure of such systems is disclosed, for example, in EP-A 461 685, DE-A 36 43 690 and US 5,244,557. An electrochromic glazing system typically has the following layer sequence: glass sheet—transparent electroconductive layer—electrochromic electrode—electrolyte—counterelectrode—transparent electroconductive layer—glass sheet.
In these systems, the solid electrolytes have the job of transporting cations to the electrochromic electrode or away from the electrode, depending on the polarity of the applied electric field. This process causes the electrochromic electrode its color to change. Solid electrolytes which are suitable for use in electrochromic systems have to satisfy a multiplicity of different requirements. They must have high electrical conductivity and high optical transparency in the visible spectral region, and in addition they must be usable in a broad temperature range without impairment to their optical, electrical and mechanial properties. Further requirements include, for example, good adhesion properties so that a stable multilayer system is achieved with the other layers of the glazing system, and good plastic deformability in order also to enable the production of curved panes, for example for use in automobiles.
U.S. Pat. No. 5,244,557 discloses an electrochromic glazing system having an electrolyte of polyethylene oxide and P
2
O
5
. EP-A 392 839, EP-A 461 685 and EP-A 499 115 disclose solid electrolytes containing polar polymers based on polyethylene oxide, polyethylene oxide copolymers or graft copolymers, and conductive salts which are soluble in these polar polymers, in particular Li salts. The solid electrolytes are prepared by dissolving the starting materials in suitable organic solvents, coating the substrates therewith, and re-evaporating the solvent. However, long drying times are necessary to remove the solvents completely. Thus, US 5,244,557 discloses drying times of 20 hours and EP-A 392 839 discloses drying times of 8 hours. The processes are therefore inconvenient and expensive.
WO 98/44576 discloses a process for the production of separator, electrode and solid electrolyte films containing electrochemically active and/or electrochemically inert solids, for use in lithium ion batteries. The specification also proposes the use of films of this type in electrochromic systems. However, the use of the battery films in the area of electrochromic glazing systems is afflicted with a number of disadvantages. The solid electrolytes disclosed have inadequate transparency, or none at all, for use in electrochromic glazing systems. Plastic deformability and good tack are properties which are undesired in lithium ion batteries, but which a solid electrolyte for electrochromic glazing systems should have. Furthermore, solid electrolytes for the battery area are restricted to aprotic systems.
It is an object of the present invention to provide a polymeric solid electrolyte which has good transparency, good conductivity and good mechanical properties and can be converted in a simple manner into electrochromic glazing systems.
We have found that this object is achieved by optically transparent polymeric solid electrolytes having a light transparency of >80% and a conductivity of greater than 10
−6
S/cm at 20° C., comprising a polymeric binder, a filler, a conductive salt, an ion-solvating plasticizer and, if desired, further additives and auxiliaries, by a process for the production of solid electrolytes of this type, and by their use in electrochromic systems and displays.
Suitable polymeric binders are in principle all thermoplastically processable polymers having adequate transparency. Particularly suitable are thermoplastics which have a light transparency of greater than 80% in the UV/VIS region. Examples of suitable polymers are polyacrylates, in particular those comprising acrylates or methacrylates of the general formula H
2
C═CHR
1
—COOR
2
, where R
1
is methyl or hydrogen, and R
2
is a straight-chain, branched or cyclic hydrocarbon radical, for example methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-amyl, isoamyl, sec-amyl, tert-amyl, neopentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, isononyl, n-decyl, n-undecyl, n-dodecyl, cyclohexyl, 3,3,5-trimethylcyclohexyl, isobornyl, vinyl or allyl groups. In a particular embodiment, the R
2
radicals can also carry one or more substituents, in particular chlorine or fluorine. Examples thereof are 2,2,2-trifluoroethyl, 2,2,3,3-tetrafluoropropyl and 1,1,1,3,3,3-hexafluoroisopropyl groups. It is also possible to employ mixtures of two or more acrylates.
It is also possible to employ copolymers of acrylates with one or more comonomers. Particularly suitable comonomers are the following:
Acrylamides and methacrylamides. Possible substituents on the amide nitrogen of acrylamide or methacrylamide, in addition to hydrogen, are the groups mentioned above under R
2
. It is also possible to employ suitable imides, for example maleimide.
Acrylonitrile or methacrylonitrile.
Styrene derivatives of the formula
The radical R1 is preferably hydrogen or methyl, and the radicals R2 and R3 are preferably hydrogen or hydrocarbon radials. The preferred comonomer is styrene.
Straight-chain, branched and/or cyclic C
2
— to C
20
-olefins, such as ethylene, propylene, 1-butylene, 2-butylene, butadiene, isoprene, 1-pentene, 2-pentene, 3-pentene, 1-hexene, 2-hexene, 3-hexene, 2,4-hexadiene, heptenes, octenes, nonenes, decenes, cyclohexene and norbonene.
The preferred comonomers are ethylene, propylene and 1-butylene.
Particularly preferred thermoplastically processable binders are the polymers usually employed for the production of optical components from plastics. Polymers of this type and their properties are described, for example, in “Optical Plastics” (Ullmann's Encyclopedia of Industrial Chemistry, 6
th
Edition, 1998, Electronic Release). Examples of such polymers are polymethyl methacrylate, polycyclohexyl methacrylate, copolymers of cyclohexyl methacrylate and methyl methacrylate, copolymers of cyclohexyl methacrylate and/or methyl methacrylate and styrene, polystyrene, styrene-acrylonitrile copolymers, copolymers of styrene and maleic anhydride, polycarbonates, for example those made from bisphenol A and phosgene, polyvinylbutyral, partially or fully hydrolyzed polyvinyl acetate/polyvinyl alcohol and copolymers thereof, for example ethylene/polyvinyl acetate copolymers, diphenyl sulfide carbonate, polytrifluoromethylstyrene, polymethylpentene, and cellulose esters, for example cellulose acetate, cellulose propionate and cellulose acetobutyrate. It is also possible to employ suitable thermoplastic polyurethanes, polyolefins or polyesters, such as polyethylene terephthalate or polybutylene terephthalate.
It is also to employ mixtures of two or more different polymeric binders, provided that the polymers are mutually compatible. The molecular weight of the polymers can be selected depending on the desired properties of the solid electrolyte. The glass transition temperature of the polymer employed should preferably be below −30° C. The polymeric binder is usually present in an amount of from 5 to 97% by weight, based on all constituents of the solid electrolyte. The solid electrolyte preferably contains from 10 to 80% by weight, particularly preferably from 10 to 50% by weight, of the filler.
The solid electrolyte according
Bauer Stephan
Bronstert Bernd
Burkhardt Uwe
Möhwald Helmut
Neuss Michael
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