CA2265190A1 - Process for producing an ion storage layer for electrochromic systems - Google Patents

Abstract

Process for producing an ion storage layer from vanadium oxide or niobium oxide, or from a vanadium oxide or niobium oxide comprising lithium ions, for an electrochromic layer system, in which the ion storage layer is produced from an aqueous solution on a substrate by a sol-gel process within a temperature range from 40 to 150°C.

Description

Le A 32 912-Foreign Countries TS/ngb/NT

Process for producing an ion storage layer for electrochromic systems The present invention relates to a process for producing an inorganic ion storage layer for electrochromic systems with controllable transparency for light.
It has not been possible to date to regulate the transparency of vehicle windows to electromagnetic radiation. To date, phototropic glasses have been used only as spectacle lenses, and feature only a relatively small change in transmission.
Windows in buildings have to date been darkened using curtains, shutters, rollers or other movable mechanical elements.
Electrochromic devices can, therefore, be employed in a wide variety of ways.
An overview may be given by the following examples:
1. Vehicle glazing (windows or car sunroofs) An electrochromic device is suitable for anti-sun or anti-dazzle use in motor vehicles. The front, side and rear windows or sunroofs can maybe included.
The degree of darkening can be adapted continuously and in zones to the needs of the driver, to the sun's position and to the current driving situation.
Integration into a computer-controlled control system is an option. A further option is the combination of the active element with a laminated glass unit, such as the application of a film system to the safety windows.
The transparency of the windows can be controlled manually or auto-matically, a feature which can be utilized for effective anti-dazzle protection when travelling at night, automatic adaptation of the level of lightness when entering and emerging from tunnels and mufti-storey/underground car parks, and for protection against break-in and robbery from the parked vehicle, by preventing sight of the vehicle interior. Excessive heating of the interior in summer, especially when the vehicle is parked, can be prevented.

Le A 32 912-Foreign Countries (cf. e.g. EP-A-0 272 428) 2. Glazing in buildings (electrochromic window) In buildings, electrochromic systems are suitable for use for darkening the windows and skylights of buildings, living areas, working areas or green-houses as a form of controllable protection from sunlight (visible spectral range) and against heat (IR range) and as visible screening (visible spectral range). To protect against break-ins, the glazing of counters in banks or of shop windows can be darkened at the push of a button. Glass doors can be made visible automatically when approached in order to avoid injuries. The possibility of producing virtually all shades of colour also permits the glazing to be incorporated as a design element into the facade of a building. The energy consumption for control of the transparency of large areas of window is low, especially when the memory effect of the system can be utilized and energy is consumed only in the switchover phase. Combination with a heat insulation glazing (K glass) is highly suited for ensuring dynamic control of solar irradiation by a "smart" window. Consequently, an electrochromic system can contribute to regulating and limiting the energy required for air conditioning.
The system can also be supplied with a voltage by means of solar modules. A
photosensitive sensor can determine the degree of solar irradiation and thus control the degree of light transmission accordingly.

3. Display elements The possibility of attractively coloured design and the large-scale depiction of any desired indicia, e.g. letters, numbers, signs and symbols (which can be produced by means of suitable structuring techniques), provides a medium Le A 32 912-Foreign Countries which is of interest for advertising. Decorative and informative effects are readily possible.
In addition to the possibility of arranging the system between glass plates there is also the alternative of using two or just one transparent plastics film as a support. By this means it is possible to realise posterlike advertising media with alterable information.
Electrochromic devices can be used for small display elements such as faces of clocks or dials of measuring instruments, displays for a wide variety of uses and for large display elements such as traffic signs, advertising columns, displays at railway stations and airports, or for guided parking systems.
Their use as a variable line marking system (pitch boundaries, etc.) in sports halls is another possibility.
They can be used generally wherever information is to be made visible.

4. Optics In optics the use of electrochromic systems is possible both in combination with glasses, lenses and filters of other optical devices and also as a stand-alone, actively utilized component. A further possibility is that of application as protection for optical detection systems against dazzle. The system is likewise suitable as a controllable filter system for photographic processes.

5. Mirrors An electrochromic device can also be employed as a dimmable mirror - for example, for a car exterior or internal rearview mirror which can be darkened by applying an electrical voltage, so preventing the driver from being dazzled by the headlights of other vehicles (c~ e.g. US-A-3,280,702, US-A-Le A 32 912-Foreign Countries 4,902,108, EP-A-0 435 689, US-A 5,140,455). Disadvantageous in prior art systems (solution systems) is the lack of colour homogeneity following prolonged operation (segregation), especially in the case of large-sized mirrors (e.g. lorry mirrors). An increase in the viscosity of the solution system by adding polymeric thickeners is described (e.g. US-A-4,902,108).

6. EMI shielding An electrochromic device can also be used as a variable filter element for the modulation of electromagnetic radiation within certain wavelength ranges.
Electrochromic devices normally consist of a pair of glass plates, one of them being mirrored in the case of a mirror. One side of these plates is coated with a transparent electrically conductive layer of, for example, indium-tin-oxide (ITO). A cell is constructed from these plates by fixing them with their electrically conductively coated sides facing one another, the cell between the plates comprising the electrochromic system, which in certain cases includes an ion storage layer.
The cell is tightly sealed. By way of the conductive layer, the two plates can be contacted electrically, and controlled, separately.
In the case of the electrochromic solution systems known from the prior art cited above there are, present in a solvent, pairs of redox substances which following reduction and oxidation, respectively, form coloured free radicals, cationic free radicals or anionic free radicals which are chemically reacted. Examples of such redox couples are the viologen systems, which have been known for a long time.
As the pair of redox substances, or redox couples, in such cases use is made of one reducible and one oxidizable substance. Both are colourless or have only a weak coloration. Under the influence of an electrical voltage, one substance is reduced and the other oxidized, with at least one becoming colored in the process. After the Le A 32 912-Foreign Countries voltage is switched off, the two original redox substances are formed once more, which is accompanied by the disappearance or fading of the colour.
US-A-4,902,108 discloses that suitable such redox couples are those where the reducible substance has at least two chemically reversible reduction waves in the cyclic voltammogram and the oxidizible substance, correspondingly, has at least two chemically reversible oxidation waves. Systems of this kind are suitable primarily for anti-glare car rearview mirrors. Since these are solution systems, their use in electrochromic windows does not come into consideration under normal circum stances.
Also known are systems where the actual electrochromic redox couple is dispersed in a polymer matrix (see e.g. WO-A-963475).
Combinations of inorganic electrochromic components, such as W03 , Ni0 or Ir02, for example, are likewise known and are suitable as components in an electrochromic window (see e.g. US-A-5,657,149, Electronique International No. 276, 16 (1997);
S aint-Gobain).
These inorganic electrochromic components can be applied to the conductive substrate only by vapour deposition, sputtering or a sol-gel technique. The result of this is that systems of this kind are very expensive to produce. In the effort to replace an inorganic component by an organic polymer component, electrochromic systems based on the electrically conductive polymer polyaniline (PANI) and W03 as complementary electrochromic materials, for example, have been disclosed (see e.g.
B. P. Jelle, G. Hagen, J. Electrochem. Soc., Vol. 140, No. 12, 3560 (1993)).
The attempt has also been made to employ systems without an inorganic component, in which the ITO or SnOz coat (counter-electrode) is intended to act as a complemen tary electrochromic component to substituted poly(3,4-ethylenedioxythiophenes) (US-A-5,187,608).

However, it is found that electrochromic systems of this kind are incapable of ensuring a sufficient number of switching cycles without altering the device properties, since, apparently, the ITO or Sn02 coat degrades after a number of switching cycles and/or the intercalation of Li ions added is not reversible. For reversibility and hence ultimately for cycle stability there is a need for an ion storage layer, which to date it has only been possible to produce by vapour deposi-tion, sputtering or a sol-gel technique under drastic heat treatment conditions. The latter condition of preparation rules out the use of plastics substrates.
It is an object of the present invention to develop a production process for a suitable inorganic ion storage layer, which does not have the above-mentioned disadvantages of the production processes known to date. In particular, the production process should be sufficiently gentle that even plastics substrates can be used in electrochromic systems.
It has now been found that an inorganic ion storage layer can be produced from vanadium oxide or niobium oxide, or from vanadium oxide or niobium oxide comprising lithium ions, by a very gentle sol-gel process.
According to one aspect of the present invention, there is provided process for producing an ion storage layer from vanadium oxide or niobium oxide, or from a vanadium oxide or niobium oxide comprising lithium ions, for an electrochromic layer system, in which the ion storage layer is produced from an aqueous solution on a substrate by a sol-gel process within a temperature range from 40 to 150°C.

- 6a -The present invention further provides a process for producing an ion storage layer from vanadium oxide or from a vanadium oxide comprising lithium ions for an electrochromic layer system, where the ion storage layer is produced from an aqueous solution by a sol-gel process within a temperature range from 40 to 150°C.
Preference is given to layers of inorganic ion stores based on vanadium oxide or niobium oxide, of the formulae (I) to (VI ) V205 (I) LixV205 (II) LixV205+x/2 (III) Nb205 (IV) Le A 32 912-Foreign Countries _7_ LixNb20g (V) LixNb205+x/2 (VI) where x represents numbers from 0.001 to 5, preferably from 0.001 to 3.
The ion storage layers can be produced by a very gentle sol-gel process.
The procedure is as follows:
An aqueous solution of ammonium metavanadate (NH4V03) or ammonium metaniobate (NH4Nb03) is treated - by stirring, for example - with a canon ex-changer in order to replace the ammonium canon by protons. Following removal of the canon exchanger by filtration, the resulting solution is left to stand (ageing). The time for which the solution is required to rest depends on the ambient or solution temperature. At room temperature, for example, the solution should be left to stand for at least 3 hours. At higher temperatures even markedly shorter times are sufficient, for example just 30 minutes.
Subsequently, the solution is applied - for example, by pouring, spraying or the like -to the electrically conductive side of the substrate which is subsequently heat-treated at temperatures of from 40 to 150°C, preferably from 40 to 130°C.
In this way a layer of the ion store is obtained which has excellent reversibility in respect of the lithium ion intercalation and decalation.
The compounds of the formulae (I) to (VI) are commonly known compounds which are obtainable commercially or can be prepared by commonly known methods of inorgnaic chemistry (c~ e.g. Rompp Chemie Lexikon; Chem. Abstr. 1313-96-8;
Hollemann-Wiberg, Lehrbuch der Anorganischen Chemie, 71 st - 80th edition, Walter de Gruyter & Co., Berlin 1971, (e.g. pages 779-781)).

Le A 32 912-Foreign Countries _g_ To improve wetting of the substrates with the aqueous solution it is also possible to add a wetting agent (for example, a fluorosurfactant).
An Li salt can be added to the aged solution, or else the aged solution without this salt can be applied to the substrate and then heat-treated, which can be carried out under reduced pressure or at atmospheric pressure.
Suitable and preferred Li salts are LiC104, LiCF3S03, LiN(SOZCF3)z, LiCI, LiPFb.
Among these, very particular preference is given to LiCl04, LiCF3S03 and LiN(SOzCF3)z.
The compounds are widely known and obtainable commercially or can be prepared by widely known methods of inorganic chemistry.
The production process of the invention for ion storage layers in electrochromic systems can be applied to glass or different types of plastic as the substrate.
Preference is given to transparent substrates of whatever kind which are provided with an electrically conducting transparent coating or with a mirror layer.
Particularly preferred materials other than glass, especially heat insulation glass in the case of application as an electrochromic window (in layer thicknesses of 10 ~m in the case of flexible glass and thin glass up to 3 cm), are polyesters (e.g.
polyethylene terephthalate) (PET), various types of polycarbonate (e.g.
~Makrolon, APEC-HT), and polycycloolefins. In this case the polymeric substrate can be employed as a flexible film or as a thick plate. The substrate may also be in curved form.
In addition, the plastics substrates can be provided with barrier layers against water and oxygen.

Le A 32 912-Foreign Countries The production process of the invention for the ion storage layers is one production step in the overall production of an electrochromic system. In an electrochromic system the production process of the invention serves as a substep in the generation of an electrochromic layer structure as a medium with variable transmission;
in other words, under the influence of an electrical voltage the transparency of the system alters as it passes from a colorless into a coloured state.
The present invention additionally provides for the incorporation of the production process of the invention into the production of an electrochromic device.
Applications of this electrochromic device are, for example, as a window pane, car sunroof, car rearview mirror, display or optical element.
Examples:
Example 1 Production of an ion storage layer 1 (V205) a) Preparation of a sol solution for producing the ion storage layer 2.5 g of ammonium vanadate (NH4V03) are dissolved in 25 g of water, and 37.5 g of the ion exchanger Lewatit S 100 (from Bayer AG, Leverkusen, Germany) are added. The mixture is subsequently stirred at room temperture for ten minutes. Then, with rapid stirring, a further 475 g of water are added and stirring is continued for 10 minutes. The mixture is filtered and the resulting solution is allowed to stand at room temperature for 24 hours, for ageing. Finally, 0.25 g of the fluorosurfactant wetting agent Fluortensid FT
248 (from Bayer AG Leverkusen, Germany) is added. This solution is ready for use.

Le A 32 912-Foreign Countries b) Gel process The solution from Example 1 a) is applied to the conductive side of ITO glass and a uniform layer of the sol is produced using a spin coater ( 10 seconds at 1000 rpm). This is followed by heat treatment at 60°C for 24 hours. A
layer thickness measurement with the profilometer gave a result of 10 to 20 nm.
Example 2 Production of an ion storage layer 2 (LiXV205) 0.01 g of LiCF3S03 (Li triflate from Aldrich) is added to 1 g of the solution from Example 1 a), and the mixture is stirred thoroughly. As described under 1 b), this solution is applied to the conductive side of K glass (FTO) and in the course of two hours of heat treatment at 100°C an ion storage layer is formed which, however, unlike that of Example 1 b), already includes Li ions.
Example 3 Production of an ion storage layer 3 (V205) The solution from Example 1 a) is applied to the conductive side of K glass and a uniform layer of the sol is produced using a spin coater (10 seconds at 1000 rpm).
This is followed by heat treatment at 100°C for 2 hours. A layer thickness measurement with the profilometer gave a result of 10 - 20 nm.

Le A 32 912-Foreign Countries Example 4 Construction of electrochromic cells for testing the ion storage layers:
~ Application of an electrochromic polymer to an ITO substrate:
Baytron~P (aqueous dispersion of the conductive polymer PEDT/PSS
polyethylenedioxythiophene-polystyrenesulfonate, from Bayer AG) is applied from aqueous solution using a spin coater 4 times for 15 seconds each time at a speed of rotation of 1500 rpm to the electrically conductive side of an ITO
glass sheet (from Merk-Balzers, Liechtenstein, surface resistance < 15 S2/sq).
During application, the solvent is evaporated using a hairdryer.
A transparent and only very slightly bluish-coloured polymer film is obtained.
Measurement of the layer thickness with a profilometer gave a value of 0.6 pm.
~ Application of Baytron P to K-Glass:
Baytron~P is applied from aqueous solution using a spin coater 4 times for 15 seconds each time at a speed of rotation of 1500 rpm to the electrically conductive side of a K glass sheet (FTO, heat insulating sheet from Flachglas, surface resistance ~20 S2/sq). During application, the solvent is evaporated using a hairdryer.
A transparent and only very slight bluish-coloured polymer film is obtained.
Measurement of the layer thickness gave a value of 0. 6 pm.
~ Preparation of a gel electrolyte 1:
The following mixture is produced:

7.0 g of acetonitrile 2.0 g of propylene carbonate (dry) 0.7 g of PMMA (MW about 15.000) 0.3 g of CF3S0;Li (from Aldrich) Le A 32 912-Foreign Countries After all of the components have dissolved, the solution is filtered once and is ready for use.
~ Preparation of a gel electrolyte 2:
The procedure is analogous but with the following amounts of components:
7.0 g of acetonitrile 2.0 g of propylene carbonate 0.7 g of polyethylene oxide (PEO; MW about 200,000) 0.3 g of CF3S03Li (from Aldrich) ~ Production of a gel electrolyte layer 1:
The gel electrolyte 1 is applied using the spin coater to the ion storage layer 1 (30 seconds at 1000 rpm). In the course of application the highly volatile acetonitrile evaporates almost completely to leave the gel electrolyte as a layer.
~ Production of a gel electrolyte layer 2:
The gel electrolyte 2 is applied using the spin coater to the ion storage layer 1 (30 seconds at 1000 rpm). In the course of application the highly volatile acetonitrile evaporates almost completely to leave the gel electrolyte as a layer.
~ Production of a gel electrolyte layer 3:
The gel electrolyte 2 is applied using the spin coater to the ion storage layer 2 (30 seconds at 1000 rpm). In the course of application the highly volatile acetonitrile evaporates almost completely to leave the gel electrolyte as a layer.
~ Production of a gel electrolyte layer 4:
The gel electrolyte 2 is applied using the spin coater to the ion storage layer 3 (30 seconds at 1000 rpm). In the course of application the highly volatile Le A 32 912-Foreign Countries acetonitrile evaporates almost completely to leave the gel electrolyte as a layer.
~ Finishing of a complete electrochromic cell 1 and 2:
Gel electrolytes 1 and 2 are applied uniformly to the ion storage layer 1 on ITO glasses and the coated glasses are brought into contact with the Baytron P-coated sides of ITO glass substrates. This gives electrochromic layer systems which are characterized in Example 5.
~ Finishing of a complete electrochromic cell 3 and 4:
Gel electrolytes 2 are applied uniformly to the ion storage layer 2 and 3 on K
glasses and the coated glasses are brought into contact with the Baytron P-coated sides of K glass substrates. This gives electrochromic layer systems which are characterized in Examples 6 and 7.
Example 5 Cycle stability test on the electrochromic cells 1 and 2 The electrochromic cells 1 (with PMMA) and 2 (with PEO) from Example 4 are each contacted at the conductive layers of the coated ITO glasses with 1.6 V DC
voltage for a short time before the polarity of the electrical stimulus is changed.
This produces a cyclical colouring and decolouring of the cell. At the same time the change over time in the transmission of the cell is observed. It is found that systems with the ion storage layers produced in accordance with the invention exhibit stable switching behaviour (in this respect compare Fig. 1 ).

Le A 32 912-Foreign Countries Example 6 Cycle stability test on the electrochromic cell 3 The electrochromic cell 3 (with PEO on LixV205) from Example 4 is in each case contacted at the conductive layers of the coated K glasses with 1.5 V DC
voltage for a short time before the polarity of the electrical stimulus is changed. This produces a cyclical colouring and decolouring of the cell. At the same time the change over time in the transmission of the cell and the current through the system are observed. It is found that systems with the ion storage layer produced in accordance with the invention exhibit stable switching behaviour (in this respect compare Fig. 2).
Example 7 Cyclovoltametric investigation of the electrochromic cells 3 and 4 The electrochromic cells 3 (with PEO on LiXVz05) and 4 (with PEO on V205) from Example 4 are characterized by cyclovoltametry in a two-electrode setup without reference between +2 V and -2 V (pole reversal) with respect to their current-voltage characteristic lines. As can be seen in Fig. 3, the electrochemical profile of properties and hence the switching behaviour of the system can be varied by way of the choice of production conditions of the ion storage layers.

Claims (10)

1. Process for producing an ion storage layer from vanadium oxide or niobium oxide, or from a vanadium oxide or niobium oxide comprising lithium ions, for an electrochromic layer system, in which the ion storage layer is produced from an aqueous solution on a substrate by a sol-gel process within a temperature range from 40 to 150°C.

2. Process according to claim 1, characterized in that, as the inorganic ion store, compounds from the group of the formulae (I) to (VI) are employed:
V2O5 ~~~(I) Li x V2O5~ (II) Li x V2 O5+x/2~ (III) Nb2O5 ~~(IV) Li x Nb2O5 ~~(V) Li x Nb2O5+x/2 ~(VI) where x represents numbers from 0.001 to 5.

3. Process according to claim 1, 2 or 3, characterized in that an aqueous solution of ammonium metavanadate or ammonium niobate is treated with a cation exchanger in order to replace the ammonium cations by protons, the cation exchanger is filtered off, the resulting solution is left to stand and then applied to the substrate and the substrate is then heat-treated at temperatures of from 40 to 150°C.

4. Process according to claim 1, 2, 3 or 4, characterized in that, for wetting of the substrates with the aqueous solution, a wetting agent is added.

5. Process according to claim 3, characterized in that a Li salt is added to the solution which is applied to the substrate and then heat-treated.

6. Process according to claim 5, characterized in that LiC1O4, LiCF3SO3, LiN(SO2CF3)2, LiCl or LiPF6 is used as a lithium salt.

7. Process according to any one of claims 1 to 6, characterized in that the ion storage layer is loaded electrochemically with Li ions.

8. Process according to any one of claims 1 to 7, characterized in that a transparent substrate is used.

9. Process according to any one of claims 1 to 8, characterized in that a flexible film or plate is employed as the substrate.

10. Process according to any one of claims 1 to 9, characterized in that the substrate is a plastic having a barrier layer against water or oxygen.