RU2676807C2 - Electrochromic device and method for its manufacture - Google Patents

Abstract

FIELD: electrical engineering.SUBSTANCE: use: to create electrochromic devices with electrically controlled amount of light transmission. Invention consists in that the electrochromic device includes a working electrode based on tungsten oxide, a counter electrode and a polymer lithium-containing electrolyte, while a counter electrode with a high intercalation capacity with respect to lithium ions (Li).EFFECT: technical result: providing the possibility of high contrast between colored and discolored states, the achievement of maximum service life.3 cl, 3 dwg

Description

FIELD OF THE INVENTION

The invention relates to applied electrochemistry, namely to electrochromic devices with an electrically controlled amount of light transmission. According to the claimed invention, an electrochromic device consisting of a working electrode, a counter electrode and a polymer lithium-containing electrolyte is characterized by a high contrast value between the colored and bleached states, the maximum possible service life, during which the maximum number of dyeing / bleaching cycles is achieved (at least 10 ⁵ times), and can be manufactured without the use of expensive vacuum technology.

State of the art

Electrochromism as a phenomenon of color change of substances under the influence of electric current was discovered back in the 60s of the XX century, however, at present, the spread of electrochromic devices is still constrained by the complexity of their production technology and the resulting high cost.

Electrochromic devices are designed to control the light and heat flux passing through them. Structurally, electrochromic devices are a multilayer material, the upper and lower layers of which have a solid or flexible substrate or a counter-substrate made of glass or a polymeric material. A transparent electrically conductive material based on a transition metal oxide (TCO) is deposited on the inner surface of a substrate or counter-substrate, in particular, indium oxide doped with tin, or tin oxide doped with fluorine. An electrochromic layer of metal oxide, in particular: tungsten oxide, niobium, vanadium, iridium, or mixtures thereof, and / or an electroactive polymer, in particular, polyaniline or polypyrrole, or polythiophene, or their derivatives, is deposited on the surface of a transparent electrically conductive substrate material. The "substrate / transparent electrically conductive material / electrochromic layer" design, which is responsible for the controlled light transmission of the device due to dyeing / bleaching, is called the working electrode.

A transparent active layer is deposited on the surface of the transparent electrically conductive material of the backing substrate, which ensures the occurrence of a conjugated electrochemical reaction with respect to the working electrode. The “backing / transparent electrically conductive material / active layer” design is called a counter electrode, while the active layer of the counter electrode may or may not have electrochromic properties.

A layer of ionic conductor or electrolyte is located between the working electrode and the counter electrode. The electrolyte serves as a conductor of ions, usually lithium or hydrogen cations, which diffuse into the working electrode from the counter electrode and vice versa when the polarity of the external voltage applied to the electrodes changes, while the ions intercalate (penetrate) into the working electrode or counter electrode, and deintercalate (exit back) from the working electrode or counter electrode.

Therefore, to achieve the greatest coloration (tinting) of an electrochromic device designed to control the light flux, it is necessary that the counter electrode play the role of a buffer capacity for storing lithium ions and its intercalation capacity / 1, 2 / with respect to lithium ions must be consistent with the intercalation capacity of the working an electrode;

The prior art / 3 / known electrochromic device with a counter electrode from a metal mesh, included in the present description by reference. An oxidation / reduction reaction of the metal of the grid (in the preferred embodiment, a copper grid) occurs at the counter electrode at such an external voltage that ensures the absence of decomposition of the electrolyte and gas evolution. The main disadvantage of this electrochromic device is the limited service life due to the gradual destruction of the counter electrode due to the transition of the metal of the grid into a solution in the form of ions, as well as the presence of a metal grid visible to the naked eye, which interferes with the perception of objects behind the electrochromic device.

The prior art / 4 / known electrochromic device with a counter electrode based on Prussian blue: a mixture of hexacyanoferrates from KFe [Fe (CN) ₆ ] to Fe ₄ [Fe (CN) ₆ ] ₃ , mainly in the form of ferricyanide iron (II) Fe ₃ [Fe (CN) ₆ ] ₂ . The disadvantages of this electrochromic device are: self-bleaching of the counter electrode at temperatures above 50 ° C; degradation of the counter electrode by UV radiation; its low electrochemical stability in a bleached state; insufficient heat and moisture resistance. In addition, in the system of tungsten oxide and Prussian blue, the electrochemical balance necessary to completely discolor the device is not maintained, therefore, the counter electrode needs to be charged before starting work.

In the patent “Transparent counter electrodes” 151 electrochromic devices with transparent counter electrodes based on transition metal hexacyanoferrates are disclosed, the composition of which is described by the general formula [Me] ₄ [Fe (CN) ₆ ] ₃ , where Me = In, Ga, Gd, La. These counter electrodes are applied to the TCO in a galvanic manner. An electrochromic device composed of tungsten oxide and any of these counter electrodes is electrochemically stable, unlike an electrochromic device based on Prussian blue, specified in patent / 4 /, does not require preliminary recharging, and the bleaching cycle is completed in 80 seconds. According to source 151, an electrochromic device with a solid H-electrolyte worked out 10 ⁴ cycles of staining / discoloration without compromising contrast.

However, the electrochromic devices indicated in the information source / 5 / are characterized by a low contrast between the colored and discolored states due to the insufficient intercalation capacity of the counter electrodes, in addition, to stain a device 10 × 20 cm in size, a charge of 41 mC / cm ² must be skipped, and the staining cycle is completed in 120 seconds and is accompanied by a decrease in transmission from 68% to 20%.

The patent “Counter electrode for electrochromic systems” / 6 / discloses a counter electrode, nickel oxide, sprayed by reactive cathodic sputtering (magnetron method). The problem to be solved is to manufacture a counter electrode that is resistant to the action of an electrolyte. An electrochromic device with an area of 100 cm ^{2 was} implemented with a WO ₃ working electrode and a NiO (OH) counter electrode, having a transmittance of 73% in a bleached and 32% in a colored state, an operating voltage of minus 1.7 V for coloring and 0.7 V for bleaching, time response 1 min. The resistance of the TCO was 5 Ω / sq. Thus, in this patent only a laboratory sample of electrochromic glass is realized, while applying a counter electrode according to the described method to architectural glasses is a complex technological task and requires expensive equipment.

In the patent "Electrochromic devices" / 7 / a device is disclosed that uses a nickel-tungsten mixed oxide NiWO counter electrode. It was noted that the staining time was 10 minutes to 80% of the maximum, and the size of the device was not indicated, although it is known that with increasing size, the staining / discoloration time increases. Other technical parameters of the electrochromic device are not given.

In the patent "Electrochromic counter electrode" / 8 / the material of the counter electrode is disclosed - nickel oxide doped with tantalum. Application of layers is carried out by vacuum spraying. The electrochromic device is fully solid state. Specifications not shown.

Patent Electrochromic Glasses for Automobiles and Buildings 191 discloses a counter electrode material — vanadium oxide or mixed vanadium-molybdenum oxide V ₂ O ₅ / MoO ₃ . It is applied to glass by evaporation. The operating voltage of the electrochromic device is +/- 1.2 V. Other specifications are not given.

Since 1993, the Japanese Nippon Corporation has published a series of patents that disclose the formulas of counter electrodes / 10, 11 /, working electrodes / 12, 13 / and provide versions of electrochromic devices based on them.

So in the inventions claimed by Nippon Oil Co., the counter electrodes consist of an electrically conductive substrate and a plurality of capacitive elements attached to the substrate. Each of the capacitive elements consists of small particles bonded with a binder (silicone or epoxide, or epoxysilane). The electrical capacity of the particles leaves at least 1 f / g / 11 /. The size of the particles of various shapes lies in the range of 0.1-500 microns. The materials used for the manufacture of the counter electrode are: porous carbon, intercalation materials (TiS ₂ , MOS ₂ disulfides; CoO ₂ , NiO ₂ dioxides, electrochromic oxides W ₁₈ O ₄₈ , W ₂₀ O ₅₈ ) or electrically conductive polymers (polyaniline, polypyrrole , polythiophene) and mixtures thereof. To improve conductivity, a conductive material is used, for example, graphite, acetylene black, thin metal particles or conductive polymers.

The patents “Counter electrode for smart glass and smart glass” / 10, 11 / disclose smart glass (“smart window” or smart window), the counter electrode of which has a sufficiently high intercalation capacity per unit area, good mechanical and electrochemical stability. Smart glass is characterized by quick response regardless of the type of electrochromic material, high efficiency and a large number of dyeing / bleaching cycles. In this case, the electrochromic material in the composition of smart glass can be either cathodic: WO ₃ , MoO ₃ , V ₂ O ₅ , Nb ₂ O ₅ , TiO ₂ , or anodic: Cr ₂ O ₃ , MnO ₂ , CoO, NiO. The counter electrode consists of a transparent substrate and an electrically conductive material having a specific surface area of at least 10 m ² / g. As the electrically conductive material, porous carbon and electrically conductive polymers (polythiophene, polypyrrole, polyaniline, etc.) or mixtures thereof can be used. Porous metal oxides NiO, Cr ₂ O ₃ , CuO, Al ₂ O ₃ , SiO ₂ can be added to the electrically conductive material. The electrically conductive material is applied in the form of strips, straight or curved lines, gratings of straight lines, as well as any possible flat geometric shapes. The preferred configuration of capacitive particles on the surface of the conductive substrate: points or strips. The proportion of coating the surface with capacitive elements in the range from 3% to 70% / 11 /. So, the counter electrode obtained from a mixture of activated carbon with graphite and a binder has a glass area fraction covered by an opaque material equal to 20%.

In one embodiment of an electrochromic device, dyeing occurs when a voltage of plus 1 V is applied, and the optical density in the colored state changes to 1.08. Discoloration occurs when a voltage of minus 1 V is applied, and the optical density changes to 0.2. The device in one application has worked 10 ³ cycles of staining / discoloration without compromising the contrast / 10 /.

In another of the embodiments of an electrochromic device measuring 30 * 30 cm, staining takes 70 seconds. when applying a voltage of 1.5 V, and the optical density in the colored state changes to 1.5. Discoloration occurs when a voltage of minus 1 V is applied, and the optical density changes to 0.25. At a wavelength of 633 nm, the change in optical density of the device is 1.25.

The design of the electrochromic device presented in the patent / 11 / is a prototype of the invention. The disadvantage of this technical solution is the large proportion of the glass surface area covered by an opaque material, and the small intercalation capacity of the counter electrode (Q, mAh / g). The disadvantages of the electrochromic device described above lead to a decrease in the transmission of visible light and a deterioration in the appearance of the device, since the points or strips of the counter electrode are distinguishable to the naked eye from a distance of 10 m due to their size.

Thus, the main disadvantage of the known electrochromic devices is the lack of contrast between the colored and bleached states. This is due to the fact that their counter electrodes have a small intercalation capacitance with respect to lithium ions (Li ⁺ ). To increase the degree of contrast in these cases, the mass of the material of the counter electrode is increased, which inevitably leads either to an increase in the thickness of its layer or to an increase in the fraction of the surface area of the glass covered by an opaque material. An increase in the thickness of the layer of material of the counter electrode leads to such undesirable consequences as a decrease in transparency; increase in operating voltage due to increased resistance; reducing the response speed of the electrochromic device. An increase in operating voltage in turn leads to an increase in the likelihood of adverse reactions and to rapid degradation of the electrochromic device.

The aim of the claimed invention was the development of electrochromic devices with improved performance.

The objective of the invention was to develop an optimal design of an electrochromic device in which the working electrode and counter electrode have coordinated intercalation capacities, thereby achieving a high contrast between the colored and bleached states, the longest possible service life, during which the number of dyeing / bleaching cycles is at least 10 ⁵ times .

Additional technical results of the claimed invention include the simplification of the production of an electrochromic device through the use of available methods and cheaper equipment and components in the manufacture of the counter electrode.

The problem is solved in that the electrochromic device includes a working electrode based on tungsten oxide, a counter electrode and a polymer lithium-containing electrolyte, characterized in that a counter electrode with a high intercalation capacity with respect to lithium ions (Li +) is used as a counter electrode.

As a counter electrode with high intercalation capacity, a counter electrode based on lithium cobaltate LiCoO ₂ and / or lithium ferrophosphate LiFePO ₄ and / or lithium manganate LiMn ₂ O ₄ , as well as these compounds doped with manganese, iron, cobalt, nickel, vanadium, can be used. , chrome, aluminum, rare earths and other elements without limiting the list.

A method of manufacturing an electrochromic device includes the manufacture of a working electrode, a counter electrode, assembly of the electrochromic cell, its filling with a polymer electrolyte and sealing, while for the manufacture of the counter electrode use available printing methods (screen printing, flexography, gravure printing, etc.) on the surface of the counter substrate with a transparent conductive material without the use of vacuum technology.

In one embodiment of the invention, for the manufacture of an electrochromic device, a working electrode based on tungsten oxide is used, which is a 4 mm thick glass substrate with a TCO layer of tin oxide doped with fluorine, with a surface resistance of 18 Ω / sq, and an amorphous layer deposited on top of the TCO tungsten oxide with a thickness of 200-600 nm, preferably 300-400 nm, applied by sol-gel technology by the method described, for example, in / 14 /.

A counter electrode with a high intercalation capacity with respect to lithium ions / 16 / is used as a counter electrode.

For the manufacture of the active layer of the counter electrode, a composition containing a material with a high intercalation capacity with respect to lithium ions and high electrochemical stability is used. The above materials include compounds: lithium cobaltate LiCoO ₂ (theoretical capacity 278 mAh / g), lithium ferrophosphate LiFePO ₄ (theoretical capacity 170 mAh / g), lithium manganate LiMn ₂ O ₄ (theoretical capacity 148 mAh / g), which can be alloyed with manganese, iron, cobalt, nickel, vanadium, chromium, aluminum, rare earth and other elements without limiting the list. The above materials are opaque, but due to the high intercalation capacitance, they can be used in such a quantity that, after applying to the backing in the form of dots, strokes, lines, or a grid, the fraction of the surface area of the counter electrode covered by an opaque material will be minimal, and at the same time, very importantly, the maximum possible contrast between the stained and discolored states is ensured. In addition, prior to assembling the claimed electrochromic device, preliminary charging of the working electrode and counter electrode is not required.

The distance between points or lines, as well as the size of the mesh cells, are selected so that the fraction of the surface area of the counter electrode, and thereby the fraction of the surface area of the electrochromic glass as a whole, covered by an opaque material, is from 3.0% to 12.0%, the preferred embodiment execution - from 3.0% to 6.0%.

In the claimed technical solution, in contrast to the closest analogs, the fraction of the surface area of electrochromic glass, free from opaque material that interferes with the comfortable perception of objects through an electrochromic device, is 92–97%. At the same time, with the same free surface area of the glass from an opaque material, the claimed electrochromic device is characterized by a significantly higher contrast between the colored and discolored states .: Thus, in technical solution / 11 / at a wavelength of 633 nm, a change in optical density by 1.25 is achieved at 80% of the free surface area of the glass, while in the electrochromic device according to the claimed technical solution, the same contrast is achieved at 95% of the free th area of the glass surface of an opaque material.

The electrochromic device according to the present invention is characterized by a large number of dyeing / bleaching cycles, in particular: in one embodiment, the number of dyeing / bleaching cycles reaches 10 ⁵ times, while the contrast decreases by 2%, and the response time does not change.

Brief Description of the Drawings

The claimed invention is illustrated by drawings. In FIG. 1 shows the design of the working electrode, side view. With reference to FIG. 1 marked: 1 - glass substrate;

2 - transparent conductive coating;

3 - electrochromic material (WO ₃ ).

In FIG. 2 is a side view of the counter electrode. With reference to FIG. 2 are indicated:

4 - active layer of the counter electrode;

5 - transparent conductive coating;

6 - counter-support.

In FIG. 3 illustrates the construction of an electrochromic device according to the present invention.

With reference to FIG. 3 are indicated:

7 - glass substrate;

8, 12 - transparent conductive coating;

9 - electrochromic material (WO ₃ ),

10 - electrolyte,

11 - active layer of the counter electrode,

13 - glass backing;

14, 15 - electrical contacts.

The following is a detailed example of the manufacture of an electrochromic device according to the claimed invention.

The implementation of the invention consists in the fact that for the manufacture of an electrochromic device, a working electrode based on tungsten oxide is first manufactured by the sol-gel technology by the method described, for example, in / 14 /. Then make the counter electrode in one of the options described in the patent / 16 /. An electrochromic cell is assembled from a working electrode and a counter electrode, filled with a polymer electrolyte according to one of the known methods, sealed, electrical contacts are connected, and the operating voltage, dyeing / bleaching time, contrast and the number of cycles are measured.

The operation of the electrochromic device consists in supplying a constant voltage of 1 or 1.5 V via electrical contacts (14, 15), while for the purpose of staining, the negative pole is fed to the working electrode associated with tungsten oxide, and the positive pole to the counter electrode. At the working electrode, tungsten oxide is reduced by a reversible redox reaction, including transitions of lithium ions. The process accompanied by the occurrence of blue staining is described by the equation:

WO ₃ + xLi + xe ^- ↔Li _x WO ₃

In this case, an electrochemical redox reaction takes place on the counter electrode, which is described by the equation in general form (using lithium ferrophosphate as an example):

LiFePO ₄ -xLi-хе ^- ↔Li _1-x FePO ₄

When the voltage changes to the opposite polarity, the reverse processes occur on the electrodes, and the device becomes discolored.

An electrochromic device according to the technical solution given in the example has the following characteristics:

- working voltage for coloring - no more than minus 1.5 V;

- operating voltage for bleaching - not more than plus 1.0 V;

- optical density in a bleached state at a wavelength of 633 nm - 0.2;

- optical density in the colored state at a wavelength of 633 nm - 1.5;

- the difference in optical density (contrast) - 1.3;

- the proportion of surface area covered by an opaque material - 5%

- the number of staining / bleaching cycles is more than 50,000.

Thus, as a result, it was possible to manufacture an electrochromic device with high contrast, a large number of dyeing / bleaching cycles in comparison with analogs, and not requiring expensive vacuum technologies to be manufactured.

Information sources

/ 1 / Holleman, A.F .; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. p. 794 ISBN 0-12-352651-5.

/ 2 / Kulova T.L. et al. Intercalation of lithium into thin films of amorphous silicon. // Physics and technology of semiconductors. - 2006. - T. 40, no. 4. - S. 473-475: ill. - (Amorphous, glassy and porous semiconductors). - Bibliography: p. 475 (10 titles). - ISSN 0015-3222.

/ 3 / Patent US 5161048, IPC: G02F 1/01. Electrochromic window with metal grid counter electrode and acidic polyelectrolyte (translation: "Electrochromic window with a metal mesh counter electrode and acid polyelectrolyte").

Published: November 3, 1992. Status: terminates.

/ 4 / Patent RU 2534119 (C2), IPC: C09K 9/02, G02F 1/15. Electrochromic device with lithium polymer electrolyte and method for its manufacture. Published: 11/27/2014. Status: valid.

/ 5 / Patent US 5209980, IPC: Н01М 10/052, Н01М 10/0565, C09K 9/00, G02F 1/15, Н01В 1/12.

Transparent counterelectrodes (translation: "Transparent counter electrodes"). Published: 05/11/1993. Status: terminated.

/ 6 / Patent US 5164855, IPC: G02F 1/01. Counter electrode for electrochromic systems (translation: "Counter electrode for electrochromic systems"). Published: November 17, 1992. Status: valid.

/ 7 / Patent US 8228592, IPC: G02F 1/153. Electrochromic devices (translation: "Electrochromic devices"). Published: July 24, 2012. Status: valid.

/ 8 / Patent US 6859297, IPC: G02F 1/153, G02F 1/00. Electrochromic counter electrode (translation: "Electrochromic counter electrode"). Published: 02/22/2005. Status: valid.

/ 9 / Patent US 5598293, IPC: G02F 1/153. Electrochromic glass for use in cars and buildings (translation: "Electrochromic glass for cars and buildings"). Published: 1/18/1997. Status: valid.

/ 10 / Patent US 5940202, IPC: G02F 1/155. Counterelectrode for smart window and smart window (translation: “Counter electrode for smart glass and smart glass”). Published: 08/17/1999. Status: valid.

/ 11 / Patent US 5708523 (A), IPC: G02F 1/155. Counterelectrode for smart window and smart window (translation: “Counter electrode for smart glass and smart glass”). Published: 1/13/1998. Status: valid.

/ 12 / Patent US 6118573 IPC: G02F 1/155. Electrode for electrochromic device and electrochromic device. Published: September 12, 2000. Status: terminated.

/ 13 / Patents EP 0851271 (B1), IPC: G02F 1/15, G02F 1/155. Electrode for electrochromic device and electrochromic device. Published: February 26, 2003, Byull. No. 2003/09. Status: valid.

/ 14 / Patent US5277986, IPC: B32B 15/00. Method for depositing high performing electrochromic layers. Published: January 11, 1994. Status: terminated.

/ 15 / Patent RU 2524963, IPC: G02F 1/15, C09J 139/06, C09J9 / 02. Electrically conductive adhesive for electrochromic devices. Published: 08/10/2014. Status: valid.

/ 16 / Patent RU 2609599, IPC: G02F 1/155, G02F 1/15, C01D 15/00, G02F 1/153. A counter electrode for an electrochromic device and a method for its manufacture.

Posted: 02.02.2017. Status: valid.

Claims (3)

1. An electrochromic device comprising a working electrode based on tungsten oxide, a counter electrode and a polymer lithium-containing electrolyte, characterized in that a counter electrode with a high intercalation capacity with respect to lithium ions (Li ⁺ ) is used as a counter electrode. 2. The electrochromic device according to claim 1, characterized in that a counter electrode based on lithium cobaltate LiCoO ₂ and / or lithium ferrophosphate LiFePO ₄ and / or lithium manganate LiMn ₂ O ₄ , as well as the aforementioned, is used as a counter electrode with a high intercalation capacity compounds doped with manganese, iron, cobalt, nickel, vanadium, chromium, aluminum, rare earths and other elements without limiting the list. 3. A method of manufacturing an electrochromic device according to claim 1, including the manufacture of a working electrode, a counter electrode, assembly of the electrochromic cell, its filling with a polymer electrolyte and sealing, characterized in that for the manufacture of the counter electrode using printing methods, including screen printing or flexography, or intaglio printing on the surface of the counter-substrate with a transparent electrically conductive material without the use of vacuum technology.

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