Electrochromic Devices Comprising Metal Salts in an Ion Conductive Material

Europaisches Patentamt 3 European Patent Office 00 Publication number: 0 392 694 Office europeen des brevets A2

EUROPEAN PATENT APPLICATION

@ Date of filing: 27.03.90

® Priority: 14.04.89 US 338261 © Applicant: FORD MOTOR COMPANY LIMITED Eagle Way © Date of publication of application: Brentwood Essex(GB) 17.10.90 Bulletin 90/42 © GB

Applicant: FORD-WERKE AKTIENGESELLSCHAFT Werk Kb'ln-Niehl Henry-Ford-Strasse Postfach 60 40 02 D-5000 Koln 60(DE) © DE

@ Inventor: Demiryont, Hulya 7259 Appoline Dearborn, Michigan 48126(US)

© This invention is directed to an electrochromic metal salts and an ion conduction enhancer in an ion device which comprises a colorable electrochromic conductive material. matrix layer (40) consisting essentially of certain CM < 3C> ^- O> o COPPER CO 36' ' CHLORIDE 6 • o • o • O • o ju v\> dJU 6 o o . CM Oo O •O'0'lol'<)o0t!'c;»o» 40- O» o • Oo0o0|.o0.0o00.0o O> 0»O •0»0*'o»o«oo»o oe.o.o Ca|oOoOoO.Q 34- 3Z V/////A 30^ a. Ill FIG.2

Xerox Copy Centre EP 0 392 694 A2

ELECTROCHROMIC DEVICES COMPRISING METAL SALTS IN AN ION CONDUCTIVE MATERIAL

The present invention relates to electrochromic 4,652,090; 4,505,021 ; and 4,664,934. devices which exhibit coloration and bleaching In such devices, the electrochromic film usually thereof due to an induced electric field. More par- comprises an inorganic metal oxide material, most ticularly, this invention relates to electrochromic commonly a transition metal oxide, in particular: devices which include a layer comprising metal 5 tungsten oxide. When tungsten oxide is the elec- salts dispersed or dissolved in an ion conductive trochromic material, the electrolyte layer is adapted material. Herein this layer is termed an to provide a positively charged light cation, prefer- "electrochromic matrix material layer". ably, a proton or a lithium ion. The electrolyte layer In an electrochromic device, a may be a liquid electrolyte solution like lithium physical/chemical change is produced in response 70 perchlorate in propylene carbonate or a gel elec- to an induced electric field. The result is a change trolyte like polyvinyl butyral methanol doped with in the reflective (or transmissive) properties of the LiCI. The electrolyte layer may also be a solid device with respect to electromagnetic radiations, electrolyte which comprises polymers or e.g., UV, visible and IR radiations. Such devices, copolymers containing acidic groups such as poly- one embodiment being shown as item 10 in Figure 75 styrene sulfonic acid, propylene oxide or polyethyl- 1, generally comprise a film'of electrochromic ma- ene oxide. terial 12 and an ion conductive insulating layer 14 It would be desirable, however, to have an which functions as an electrolyte layer. The film electrochromic device which comprises less layers and the electrolyte layer are in surface contact with and is hence less complex to fabricate. Addition- each other for exchange of ions between the elec- 20 ally, it would be desirable if the device, in addition trochromic film and the electrolyte layer. Two con- to being able to reduce transmission of visible light, ductive electrode layers, 16 and 18 in Figure 1, at would also be able to substantially reduce trans- least one of them being transparent, are disposed mission of IR wavelength radiation, i.e., keep radi- on the opposite outer surfaces of the film and the ation of the type which generates heat from pass- electrolyte layer to provide means for applying a 25 ing through the device. This would be particularly voltage across the combined thickness of the elec- useful if the device is used as a window of a trochromic film and the electrolyte layer. As shown building or automobile. in Figure 1, electrode layers are provided on sub- The present invention is directed to an elec- strates 20 and 22, which substrates may be of a trochromic device comprising a substrate; a first material such as glass. Depending on the ion pro- 30 electrode member provided on the substrate; an viding and ion storage capacity of ion conductive electrochromic matrix material layer in contact with layer 16, a counter electrode located between ion the first electrode member; and a second electrode conductive layer 14 and electrode layer 18 may be member in contact with the electrochromic matrix used. The electrodes are provided with external material layer, at least one of the first and second electrical leads 24 and 26 connected to a voltage 35 electrode members being transparent, the elec- providing source 28. Application of a voltage of trochromic matrix material layer consisting essen- proper polarity across the electrodes causes color- tially of a substantially uniform mixture of: (i) a ation of the electrochromic layer. By reversing the metal salt component selected from the group con- polarity of the applied voltage, the colored elec- sisting essentially of halides, acetates, nitrates, sul- trochromic layer will be uncolored (bleached). 40 fates, and phosphates of metals selected from the Changing from the bleached state to the colored group consisting essentially of copper, cobalt, nick- state or from the colored state to the bleached el, lead, molybdenum, rubidium and tin; (ii) an ion state is termed "switching". The electrochromic conductive material component selected from a material may be "persistent" in its colored state group consisting essentially of solid electrolytes which means that it has the ability to remain, after 45 and gel electrolytes; and an ion conduction enhan- removal of the electric field, in the absorptive state cer component selected from the group consisting to which it is changed, as distinguished from a essentially of lithium salts and sodium salts. Prefer- substantially instantaneous reversion to the initial ably, the metal salt is present in the matrix layer in state. The length of time a material is persistent is an amount sufficient to provide a maximum thick- called its "open circuit memory" or simply 50 ness of between about 500 to 1000A of the metal "memory". Electrochromic devices of this type on an electrode member when a voltage is applied have been described for several uses, such as for across the electrodes. The device may further image display, for light filtering, etc. See, e.g., U.S. comprise a second substrate adjacent to the sec- Patent Nos. 3,708,220, 4,194,812; 4,278,329; ond electrode member. According to another as- 4,645,308; 4,436,769; 4,500,878; 4,150,879; pect of the invention, it is directed to the method of EP 0 392 694 A2 making the above device. layer; and a second electrode member. The elec- When a voltage is applied across the electrochromic matrix material layer (prior to application trodes of the device, the electrode member which of a voltage across the electrode members) con- functions as the cathode takes on a metallic ap- sists essentially of a substantially uniform mixture pearance which makes the device useful as a dis- 5 of (i) a metal salt component, (ii) an ion conductive play device. Additionally, embodiments of this de- enhancer component and (iii) an ion conductive vice are particularly useful as windows of buildings material component. The device may further com- or automobiles since they are capable of more prise a second substrate adjacent to the second effectively reflecting IR radiation than are conven- electrode member. tional electrochromic devices. Thus embodiments 70 One aspect of the invention will be further of the present invention device, if used as windows, understood by reference to Figure 2. This figure offer an enhanced ability over prior art electroch- depicts a cross sectional view of an embodiment of romic devices to keep heat out of the building or a device 30 according to the invention taken along automobile, while at the same time being capable a line perpendicular to a surface of a substrate of of keeping heat within the building or automobile 75 the device, before and after application of a voltage from escaping through the device. This is in addi- across the electrodes of the device. The device 30 tion to the ability of these devices to control the in Figure 2 comprises glass substrate 32 in contact amount of visible light which may enter the building with transparent electrode member 34 and glass or vehicle. Still further, it has been found that substrate 36 in contact with transparent electrode embodiments of the device of the present invention 20 member 38. The device further comprises a layer are able to be switched to the colored state by of electrochromic matrix material 40 according to means of a relatively low voltage applied across the present invention, shown before, "a", and after, the electrodes. "b", application of a voltage across the electrodes. The thickness of the metallic layer formed dur- The electrochromic matrix layer 40 (before applica- ing operation of the device and hence the cor- 25 tion of a voltage across the electrodes) consists responding reduction in transmission of radiation essentially of a substantially uniform mixture of by the device can be controlled by the length of components (i), (ii), and (iii) as described above. In time a voltage is applied across the electrodes of the particular embodiment shown in Figure 2, these the device. That is, the longer the voltage is ap- components are copper chloride, lithium nitrate and plied, the thicker the metallic layer formed with a 30 polyvinyl butyral gel, respectively. Section "a" of corresponding increased reduction in transmission the matrix material layer 40 of the Figure 2 device of radiation through the device. Thus the device 30 shows the copper chloride (metal salt compo- advantageously has a variable and controllable nent) substantially uniformly dispersed throughout transmittance. According to aspects of the inven- the matrix layer. Although not shown, the ion con- tion comprising a linear cathodic electrode which is 35 duction enhancer also would be substantially uni- discussed in detail hereinafter, it is also advanta- formly dispersed throughout the matrix material geously possible to provide a device having a layer 40, section "a". This particular embodiment metallic layer of graded thickness so as to provide of the matrix material layer would appear light different portions of the device with varying trans- yellow in color as initially provided in the device, mission levels. 40 i.e., prior to application of a voltage across the The invention will now be described further, by electrodes. The intensity of the color of the initial way of example, with reference to the accompany- transparent, yellow matrix layer would depend only ing drawings, in which : on the concentration of the copper chloride in the Figure 1 is a schematic representation of an matrix material since the ion conduction enhancer electrochromic device, in cross section, according 45 present in the matrix material is colorless. Increas- to the prior art; ing the amount of ion conduction enhancer, how- Figure 2 is a schematic representations of an ever, serves to increase the conductivity of the ion embodiment of an electrochromic device, in cross conductive material component (i.e., the electro- section, according to this invention, before and lyte) which, in turn, increases the rate at which a after a voltage is applied across the electrodes of 50 metal layer is formed at an electrode member the device; and when a voltage is applied. Figure 3 is a schematic representation of an During operation of the device, a voltage is embodiment of an electrochromic device, in cross applied across the electrodes by means of leads section, according to another aspect of this inven- 46 and 48 connected to a d.c. voltage source 50 as tion. 55 shown in Figure 2. When a voltage is applied As disclosed above, the electrochromic device across the electrodes, it is believed that the metal of this invention comprises a substrate; a first elec- ions (cations) of the metal salt present in the matrix trode member; an electrochromic matrix material material layer 40 migrate toward the electrode EP 0 392 694 A2 member of negative polarity 38 (i.e., cathode or 48. While certain theories have been suggested "working electrode") as shown in Figure 2, section above to explain the working of the invention de- "a". The metal ions would be converted to metal vice, neither their validity nor their understanding is atoms at the cathode 38 to provide a metal layer necessary for a practice of this invention. thereon and provide a metallic reflective layer to 5 As discussed above, the invention device com- the device which would inhibit transmission of im- prises a substrate on which is provided a first pinging radiation through the device. In the particu- electrode member. This electrode member may lar matrix layer described above, the matrix layer function as the cathode or anode as will be appar- (and thus the device) would change from a light ent in view of the present disclosure. Additionally, yellow transparent layer having a transmittance of w the device may further comprise a second sub- perhaps about 60% (depending on the metal salt strate adjacent the second electrode member. Gen- concentration) to an opaque (i.e., having about 0% erally, this second substrate would be employed to transmittance) layer comprising a metallic copper provide a more environmentally durable device. layer. The transparency (or opaqueness) of the The substrate material employed in the device may device after a voltage has been applied would 75 comprise any material which is stable at the tem- depend on the thickness of the metal layer (in this peratures and under the conditions of the fabrica- instance, copper) which plates out on the cathode. tion and use of the device. Commonly used materi- A thicker metal layer would provide a less transpar- als for the substrate(s) of such devices include, ent device. The anions of the metal salt (e.g., the e.g., glass, quartz, plastic, and the like and suitable chloride ions of the particular embodiment dis- 20 combination of any of them. At least the substrate cussed above) would be expected to migrate to- used adjacent the cathodic electrode will preferably ward the positive electrode member (i.e., anode) if be at least translucent, more preferably being the ion conductive material allows for the ionic transparent. Selection of the optimal material to be transport of the anion, as shown in Figure 2, sec- used for one or both substrates of the device is tion "b". In this particular embodiment of the de- 25 dependent on the particular use desired of the vice, some of the chloride ions may be oxidized to device, as will be apparent to one skilled in the art chlorine gas at the anode. The use of a counter in view of this disclosure. electrode between the matrix material layer and the The electrode members used in the device of anode of the device is useful to minimize formation this invention may be any material which is elec- of gas at the anode. U.S. Patent 4,768,865 dis- 30 tronically conductive. At least one of the electrodes closes that formation of gas at an anode of an is transparent, although both may be. This light electrochromic device may be minimized by use of transmitting, transparent electrode may be a light a grid shaped anode. transmitting film of an electrically conductive metal If the ion conductive material allows for the oxide such as doped or undoped tin oxide, indium ionic transport of the cation and anion of the ion 35 oxide, zinc oxide and the like. The transparent conduction enhancer, they would also be expected electrode member may be provided on a support to move toward the cathode and anode, respec- (i.e., a substrate, matrix material layer, counter tively. electrode layer, etc.) by any known technique, in- Generally, it has been found that the device of cluding vacuum evaporation, chemical vapor depo- this invention has a short term memory, i.e., it 40 sition, sol gel deposition, ion plating, reactive sput- readily reverts to its initial (uncolored) state when tering, pyrolytic spray deposition etc. The transpar- the applied electric field is removed. For example, ent electrode member may be formed by the so in the particular embodiment device described called thick film processes such as screen printing above, when the electric field is removed the me- or photolithographic coating. When the thick batch tallic copper layer disappears and the matrix ma- 45 film process are used, (1) a paste containing metal terial layer returns to its initial light yellow color. It compound micro particles or (2) a solution of an is believed that this switching to the initial state organic metal compound such as metal alcoholate takes place spontaneously because of the residual or its oligomer is coated and sintered to form the negative charge present in the matrix material lay- transparent electrode member. Preferably, the er. If it is desired to switch the device more rapidly so transparent electrode material is tin oxide doped to its initial state, the polarity of the applied electric with fluorine. The thickness of the transparent elec- field can be reversed. That is, a voltage of positive trode member generally falls within the range of polarity would be applied to electrode member 46 200 nm to several microns, correspondingly vary- and a voltage of negative polarity would be applied ing in transparency and resistance. The non trans- to electrode member 48. If the electric field is 55 parent electrode material may be selected from maintained in this reversed polarity for a time after light reflecting electrode materials (e.g., Al, Ag, Pt, the device has been switched to its initial state, a Ni or a metal of a metal salt used to form the metal layer will begin to form at electrode member matrix layer, e.g., Cu) or other electrode materials EP 0 392 694 A2

(e.g., Au, Pd, Cr, Ir, Ru, Rh or C). movement of the linear cathodic electrode mem- The first and second electrode members may ber. be individually selected from various configura- As will be apparent to those skilled in the art in tions, such as a continuous layer, e.g., one which view of the present disclosure, various combina- covers substantially the entire face of the matrix 5 tions of electrode member types (transparent or layer, or one which consists of a pattern, e.g., a non-transparent and continuous, patterned, mov- grid, lines, a segmented design, etc. If the anodic able or fixed) and substrate may be employed electrode member is not a continuous layer, but according to this first aspect of the invention. The rather is a patterned layer, e.g., a grid, it would preferred combination would depend on the in- need to be of suitable grid density to act as an io tended use of the device. For example, if it was effective anode. Preferably, if the anodic electrode intended to use the device as windows of buildings is a metal (non transparent) electrode member, it is or the windshield or windows of automobiles where a patterned layer of substantially smaller surface it was desired to form a uniform metallic layer, the area as compared to the surface area of the anodic device would generally comprise two substrates electrode member which is preferably transparent. 15 and both electrode members would be transparent, Still further, the cathodic electrode member may be with at least one of the electrode layers, i.e., the a movable point or line electrode, i.e., a movable electrode which will be used as a cathode, being electrode which contacts the electrochromic matrix continuous. The other electrode layer could be material layer at a point (as by means of an elec- continuous or be, e.g., a grid pattern. In this case, tronically conductive pen) or in a line (straight, 20 where the cathode is a continuous layer, the ap- curved, etc.) as shown in Figure 3. In this figure, plication of a voltage as described would cause the the electrochromic device 60 comprises a sub- entire (cathode) electrode layer to take on a metal- strate 62 on which is deposited an electrode mem- lic appearance. Another combination of electrodes ber (layer) 64, an electrochromic matrix layer 66 and substrate(s) could be used, for example, in a deposited on the electrode layer 64 and a linear 25 display device. In such a device, the working elec- metal movable electrode member 68 in contact trode (cathode) could be a transparent and pat- with a portion of the electrochromic matrix layer 66. terned and applied to a transparent substrate. The During operation of device 60, a voltage is applied other electrode (anode) could be a transparent or across the electrodes by means of leads 72 and 74 non-transparent electrode layer, which additionally connected to a d.c. voltage source 76 as shown in 30 could be continuous or patterned. It is preferred to Figure 3. In this device, electrode member 64 use as the working electrode in any of the device functions as an anode and electrode member 68 mentioned a metal grid electrode which is less functions as a cathode. Such a device is useful to likely to allow the formation of gas bubbles at this provide a metallic layer in the device of variable electrode which could decrease the optical quality dimensions which additionally may be graded in 35 of the device. Still other combinations of electrode thickness, as might be optimal in a building win- configuration and type and substrate type dow, with the metallic layer only extending part of (transparent, opaque, etc.) will be apparent to those the way down the window and the thickest portion skilled in the art in view of the present disclosure. of the metallic layer being at the top. As is shown The metal salt component of the electroch- in that figure, as linear electrode member 68 slides 40 romic matrix layer is selected from a coloring com- (to the right in the figure) along matrix layer 66, a ponent comprising metal salts selected from the layer of metal 70 plates out on the surface of the group consisting essentially of halides, acetates, matrix material in the region of the movable elec- nitrates, sulfates, and phosphates of metals se- trode member 68. This metal layer 70 becomes, in lected from the group consisting essentially of cop- effect, an electrode member (cathode) as long as it 45 per, cobalt, nickel, lead, rubidium, molybdenum is in contact with linear cathodic electrode member and tin. Mixtures of compatible salts may also be 68. Hence, as the bar is moved along the surface employed as the coloring component. Preferably, of the matrix material, a metal layer 70 is formed the metal salt is present in the layer in an amount which can continue to increase in thickness as long sufficient to provide a maximum thickness of be- as a voltage is applied. The anodic electrode layer so tween about 500 to 1000A of metal (from the metal 64 can be continuous or e.g., a grid patterned salt) on the electrode layer when a voltage is electrode. If desired, the device including the applied across the electrodes. However, the metal moveable linear cathodic electrode may include a salt may be present in the matrix layer in con- second substrate, similar in dimension to the first, centrations greater than this amount. Exemplary of adjacent the cathodic electrode member to improve 55 such metal salts are copper chloride, copper io- the durability of the device. This second substrate dide, rubidium chloride, lead fluoride, nickel chlo- may be positioned relatively close to the surface of ride, copper nitrate and cobalt nitrate. The color of the matrix layer as long as space is provided for the matrix layer of the device, before and after EP 0 392 694 A2 10

application of a voltage across the electrodes will with a faster response time (faster coloring and depend on the particular salt used. For example, bleaching) than devices employing solid electrolyte the use of a copper salt will give a generally yellow materials. Still further, use of a solid oxide elec- or green color before a voltage is applied and a trolyte material requires that the oxide have some copper metallic color after a voltage is applied. On 5 porosity in order to allow for a sufficiently interface the other hand, the use of salts of rubidium, lead, area at the electrode-matrix interface for formation nickel, molybdenum and cobalt will give the matrix of the metal layer. the respective color of the particular salt before a The preferred ion conductive host material voltage is applied and a silver like metal color after component is one having adhesive properties and a voltage is applied. As will be apparent to those w made of a polymer electrolyte such as polyvinyl skilled in the art, if a mixture of the metal salts is butyral, polyvinyl alcohol, polyacrylic acid and employed, it would be expected that a unique color polyvinyl acetate. An adhesive agent having amino would be obtained. The particle size of the metal groups such as aminosilane, vinyl pyridine, nylon, salt is sufficiently small so as to form a uniform and or copolymers thereof is often optimally used to intimate mixture (which may be a solution or dis- 75 improve adhesion to the adjacent material. Polymer persion) of the components of the matrix material. electrolytes used as ion-exchange membranes can The ion conductive material (often referred to also be used as the electrolyte in the present as an electrolyte) employed in the electrochromic invention. Among these polymers, polyvinyl butyral matrix layer is selected from a group consisting is optimum in view of weathering resistance and essentially of solid ion conducting materials and 20 adhesiveness. gel ion conducting materials. The ion conductive While the copper salts, molybdenum salts and material is a dielectric material which is conductive rubidium salts employed as the coloring compo- to ions but serves as serves as an insulator for nent herein are optimally suited to be employed electrons. The ion conductive material would need dissolved or dispersed in either a solid or gel to be ionically conducting to at least the metal ions 25 electrolyte, the salts of cobalt, nickel, lead and tin of the metal salt. Generally, the ion conductive preferably are employed in gel electrolytes for op- material would preferably have an ionic conductiv- timal performance of the device. ity of at least 10~5(ohm cm)~1 and a negligible The ion conduction enhancer of the electroch- electronic conductivity, preferably less than about romic matrix layer is selected from the group con- 10~7(ohm cm)~1. Examples of such solid ion con- 30 sisting essentially of lithium salts and sodium salts, ducting materials are metal oxides such as tan- and compatible mixtures thereof. Most preferably, talum oxide (Ta2O5 ), niobium oxide (Nb2O5), zir- such compounds are selected from nitrate salts conium oxide (ZrO2), titanium oxide (TO2), hafnium and halide salts, preferably chloride salts, of these oxide (HfC>2), alumina (AI2O3), yttrium oxide alkali metals. The preferred amount of ion conduc- (Y2O3), lanthanum oxide (La20s), and silicon oxide 35 tion enhancer to be employed in the matrix ma- (SiO2), which can be made by various techniques terial layer would depend on various factors, includ- including sol-gel technology. Other suitable solid ing the particular ion conductive material and metal electrolyte materials include magnesium fluoride, salt employed in the matrix layer, coloring rate lithium nitrate (U3N), zirconium phosphate, sodium desired, etc. Selection of the optimal ion conduc- chloride, potassium chloride, sodium bromide, po- 40 tive enhancer as well as its concentration in the tassium bromide, Na3Zr2Si2POi2, Nas YSUOi2, or matrix material layer will be apparent to one skilled Na1+xZrSixP3.xOi2. Compatible mixtures of solid in the art in view of this disclosure. electrolytes may also be employed herein. Gen- The components of the electrochromic matrix erally if the electrochromic device according to this layer, including optional components such as adhe- invention employs only one substrate, the ion con- 45 sives, background providing materials (e.g., TiO2 ductive material would preferably be a solid ma- which provides a white opaqueness particularly terial. The ion conductive material may also be a used in display devices) are combined to form a gel electrolyte such as a synthetic resin copolymer substantially uniform mixture of the components. If of b-hydroxyethyl methacrylate with 2-acrylamide- using all solid components, the particulate compo- 2-methylpropane sulfonic acid, a hydrate vinyl 50 nents could be mixed using a common solvent, copolymer (e.g., a hydrate methyl methacrylate dried and layered by a coating technique or com- copolymer), or a hydrate polyester. Exemplary of pressed into a solid material in the device. Another still other (semi-solid) gel electrolytes useful as the way to form the layer is to codeposit the various ion conductive layer are those, for example, ob- components on an electrode layer by any suitable tained by gelling an electrolytic aqueous solution 55 technique, for example, by vacuum deposition, with a gelling agent (e.g., polyvinyl alcohol, CMC, chemical vapor deposition, electrolytic, thermal agar-agar or gelatin). Gel electrolytes are preferred evaporation, sputtering, and the like. Still another in this invention because they provide the device way to form the solid matrix layer, according to sol- 11 EP 0 392 694 A2 12 gel techniques, it to combine the metal salt, the rior building partitions. This device may also be materials necessary to form the electrolyte by sol- used as sunroofs, moonroofs, windows in auto- gel techniques and the ion conduction enhancer mobiles and buildings, including skylights in order and let the material solidify. The gel electrolyte to reduce visible and IR transmissions. Still other matrix layer can be applied on one of the 5 adaptions of the device and method of this inven- electrode/substrate combinations and then the oth- tion will be apparent to those skilled in the art in er electrode/substrate combination assembled view of the disclosure. therewith to form the device. The same procedure The invention will be further understood by can be followed for solid electrolytes. Selection of referring to the following detailed examples. It the optimal method, including those not specifically 10 should be understood that the specific examples not mentioned herein, for combining the compo- are presented by way of illustration and not by way nents of the matrix layer and its method of its of limitation. deposition will be apparent to those skilled in the art in view of the present disclosure. Usually the thickness of the electrochromic ma- 75 Example 1 trix material layer is between about 0.1 and 100 microns. When using a polymer adhesive elec- This example illustrates the use of an embodi- trolyte component the matrix layer would preferably ment of the device of this invention in controlling be between 25 and 100 microns. If the electrolyte the amount of light transmitted through a window. material is a solid inorganic material, the matrix 20 Two pieces of glass, 6" x 12" each, were coated layer would preferably be between about 0.5 and 1 with a 400 nm thick layers of fluorine doped tin micron. The thickness of the matrix may, however, oxide by pyrolytic deposition, which layers each vary considerably and is not meant to be limited to had a sheet resistance of 50 ohms/square. The those thicknesses given above. Since a small po- glass substrate/electrode layer systems allows for a tential will provide an enormous field strength 25 visible transmittance of about 78% of the visible across very thin films, thinner films are preferred light. In order to form the electrochromic matrix over thicker ones. Optimal thickness, however, also material, two different electrolyte gels of polyvinyl will be determined by the particular composition of butyral (PVB) were prepared as follows. In the first the film and the desired maximum thickness of the instance, Monsanto Butvar B-90 (trademark) pow- metal layer which is to be provided on the cathode 30 der was dissolved in methanol/isopropanol, forming of the device during coloration. Selection of optimal a gel comprising 35% methanol, 50% isopropanol, film thickness will be influenced by the properties and 15% PVB by volume. In the second instance, of the ion conductive material employed. a sheet of PVB was dissolved in glycol ether DPM As would be apparent to those skilled in the art to form a gel comprising 10%/90% PVB/ether by in view of the present disclosure, the method of 35 volume. this invention is applicable to any electrochromic Each of these viscous gels were individually device. Such devices may comprise other compo- mixed with copper chloride (CuCfe), the metal salt nents, e.g., counter electrodes, an electrochromic component, in an amount which provided the gel layer of the conventional type, e.g., WO3 etc. A with about 0.5% by weight of the copper chloride. counter electrode could be employed in this device 40 The ionic conductivity of the gel was determined to between the matrix material and the anode of of be about 10~4 (ohm cm)"1 at room temperature. the device (i.e., between layer 40 and electrode 34 This viscous gel was light yellow in color. Then in the device of Figure 2) to improve operation of LiCI was added to the gel in an amount to provide the device. A counter electrode may be formed of, about 0.5% by weight of this ion conduction enhan- e.g., WO3, doped with and alkali metal ion. This 45 cer. The ionic, conductivity of the gel was found to material is generally not meant to be electroch- increase to about 10~3 (ohms cm)"1 due to the romic. Additionally it is imagined that the device addition of the LiCI. may be of various shapes or designs. The devices To form the electrochromic device, one elec- of this invention could be used, for example, to trode coated glass substrate was first framed with a provide areas of privacy at will, e.g., by changing a 50 PVB gasket 1mm thick and 0.5 cm wide. Then one glass or plastic office wall made according to this of the viscous gel matrix materials (PVB/CuCb/LiCI) invention to a darkened wall (in part or in total) prepared above was provided on the electrode affording privacy within. The present invention layer within the area defined by the gasket. The might be used to provide the upper portions of matrix material was heated for about 1 hour at windows with the ability to be colored to reduce the 55 50 °C to dry the gel somewhat. Then the other transmission of radiation at will. This invention de- electrode/glass substrate combination was placed vice may be used for privacy as a device between against the matrix material and compressed until interior portions of automotive vehicles and as inte- the matrix material made uniform contact with each 13 EP 0 392 694 A2 14 electrode layer. In the same way, a device was substrate/electrode combination as made in Exam- formed of the second gel matrix material made ple 1 is coated with a 0.5 micron thick layer of above. WO3 by thermal evaporation of WO3 powder. This A voltage (3 volts) was then applied across the coating (counter electrode material) is then ex- electrode layers and a metallic copper color ap- 5 posed to a solution of 1 molar UCIO3 in propylene peared near the cathodic electrode side of the carbonate and colored electrolytically until 50% device in less than 1 minute, independent of the visible transmittance is obtained for the system type of PVB gel material used in the device. The (glass/electrode/counter' electrode). The system is other side of the devices appeared dark green and then taken from the solution, rinsed with distilled exhibited a few small bubbles. The devices re- 70 water and dried with blowing hot air. This colored turned to their initial appearance, i.e., light yellow in system was used as in Example 1, along with color, after the voltage source was disconnected another glass/electrode combination as made in from the devices. This took about 1 0 minutes which Example 1, to form an electrochromic device. would designate these devices as not having a A voltage ( + 2 volts) is applied to the electrode memory. The devices are cycled repeatedly by 75 adjacent the counter electrode LixW03. A metallic applying a voltage and then disconnecting the volt- copper layer develops near the other (cathodic) age source and perform very well. Application of a electrode layer. Use of the counter electrode is reversed polarity, as compared to that described seen to improve the rate of coloration of the device above, provided the metallic copper layer near the and minimizing gassing at the anode. It is believed other electrode layer. 20 that when the voltage is applied as described above, extraction of each Li+ and electron from the WO3 film is compensated by the electrodeposition Example 2 of a copper ion which converts to a metallic copper atom at the electrode which improve the formation Electrochromic devices were prepared as de- 25 rate of the metal layer. Such a device would be scribed in Example 1 except that the CuCb color useful, e.g., as a switchable window. forming salt was replaced with NiCb. The initial color of the devices was light green. When 3 volts is applied across the electrodes, a metallic nickel Claims color appeared near the electrode of negative po- 30 larity (cathode). The devices have no memory as 1 . An electrochromic device comprising a sub- seen by the rapid return of the devices to their strate (32), a first electrode member (34) provided initial appearance when the voltage is removed. on said substrate; an electrochromic matrix material layer (40) in contact with said first electrode 35 member (34), and a second electrode member (38) Example 3 in contact with said electrochromic matrix material layer (40), at least one of said first and second This example describes an electrochromic dis- electrode members (34,38) being transparent, said play device made according to the present inven- electrochromic matrix material layer (40) including tion. A device is prepared as in Example 1 using 40 a substantially uniform mixture of: (i) a metal salt Monsanto Butvar B-90 (trademark) powder except component selected from the group consisting of that the the matrix further contained TiO2 and halides, acetates, nitrates, sulfates, and phosphates Bi2O3 finely ground powder. These white powders of metals selected from the group consisting of were added to provide the matrix layer of the copper, cobalt, nickel, lead, rubidium, molybdenum device with a white appearance. As prepared, the 45 and tin; (ii) an ion conductive material component device is translucent with a light yellow color. selected from a group consisting of solid elec- When a voltage (3 volts) is applied across the trolytes and gel electrolytes; and an ion conduction electrodes, the cathodic side of the device exhibits enhancer component selected from the group con- a metallic copper color while the anodic side of the sisting of lithium salts and sodium salts. device maintains its translucent, white (light yellow) 50 2. A device according to claim 1 , wherein said appearance. metal salt is present in said matrix layer in an amount sufficient to provide a maximum thickness of between about 500 to 1 000A of the metal of said Example 4 metal salt on one of said first and second electrode 55 members when a voltage is applied across said This example further describes use of a coun- electrodes. ter electrode in an electrochromic device according 3. A device according to claim 1 , wherein said to this invention. The electrode layer of a first and second electrode members are individ- 15 EP 0 392 694 A2 16 ually selected from electrode material consisting of doped or undoped (a) tin oxide, (b) indium oxide, (c) indium tin oxide, (d) zinc oxide, and (e) mixtures of any of them. 4. A device according to claim 1 , wherein said 5 solid ion conductive material is selected from poly- meric electrolytes, and inorganic oxide electrolytes. 5. A device according to claim 1 , wherein said lithium salt and said sodium salt are selected from compounds comprising nitrates and halides of w these alkali metals. 6. A device according to any one of the pre- ceding claims, wherein said device further comprises a second substrate adjacent said second electrode member. 75 7. A device according to claim 1, wherein one of said first and second electrode members is a continuous layer and the other electrode member is a patterned layer, a sliding point or linear electrode. 20 8. A device according to claim 1 , wherein said device further comprises a counter electrode positioned between one or said first and second electrode members and the adjacent surface of said electrochromic matrix material layer. 25 9. A device according to claim 1, where at least one of said transparent surfaces is tinted. 10. A method for making an electrochromic device, which method comprises, providing a first electrode layer on a substrate, providing an elec- 30 trochromic matrix material layer in contact with said first electrode member, and providing a second electrode layer in contact with said electrochromic matrix material layer, at least one of said first and second electrode members being transparent, said 35 electrochromic matrix material layer consisting of a substantially uniform mixture of: (i) a metal salt component selected from the group consisting of halides, acetates, nitrates, sulfates, and phosphates of metals selected from the group consisting of 40 copper, cobalt, nickel, lead, rubidium, molybdenum and tin; (ii) an ion conductive material component selected from a group consisting of solid electrolytes and gel electrolytes; and an ion conduction enhancer component selected from the group con- 45 sisting of lithium salts and sodium salts.

55 EP 0 392 694 A2

PRIOR ART

FIG.l

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FIG.2

FIG.3