RU2534119C2 - Electrochromic device with lithium polymer electrolyte and method of manufacturing thereof - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to applied electrochemistry, namely to an electrochromic device with a lithium polymer electrolyte and a method of manufacturing the electrochromic device. Claimed is the electrochromic device with the lithium polymer electrolyte, which includes an operating electrode in the form of a tungsten oxide film, a counterelectrode in the form of the Prussian Blue film and a polymer electrolyte with the following composition, wt %: lithium perchlorate 8-16, ethylenecarbonate 20-30, polymethylmethacrylate polymer 10-20, propylenecarbonate - the remaining part. The method of the electrochromic device manufacturing includes the preparation of the polymer electrolyte, preparation of working and auxiliary electrodes, in particular the cathode restoration of an auxiliary electrode before the assembly in the liquid lithium electrolyte, assembly and sealing. In the process of assembly a portion of the thickened polymer electrolyte is placed between the electrodes with their compression until complete contact of the counterelectrode with a separator of the operating electrode takes place, after which the excess of the electrolyte is removed. The device sealing is carried out by means of thermal glue.

EFFECT: application of the claimed method prevents the formation of gas bubbles in the electrolyte layer.

5 cl, 3 ex

Description

The invention relates to applied electrochemistry, and in particular to an electrochromic device with a lithium polymer electrolyte, and a method for manufacturing an electrochromic device.

Known electrochromic devices with a working electrode of tungsten oxide, a counter electrode of Prussian blue, with a lithium polymer electrolyte containing solutions of lithium salts in mixed organic solvents based on alkylene carbonates, thickened with a suitable polymer, for example polymethyl methacrylate [1. M. Kucharski, T.. Lukaszewicz, and P. Mrozek, Opto-electronics Review, 12 (2), 175-180 (2004), New electrolyte for electrochromic devices. 2. US patent US 5581394, IPC G02F 1/153, 03.012.1996]. The described methods for the preparation of electrolytes for such devices include dissolving the polymer in a liquid lithium electrolyte diluted with a volatile solvent, for example tetrahydrofuran, pouring the solution on the electrode and distilling off the volatile solvent to obtain a gel electrolyte film on the electrode [1 M. Kucharski, T.. Lukaszewicz, and P. Mrozek, Opto-electronics Review, 12 (2), 175-180 (2004), New electrolyte for electrochromic devices]. The method of preparing an electrolyte for an electrochromic device according to the patent [US Patent US 5581394, IPC G02F 1/153, 01/03/2/1996] includes dissolving the polymer in liquid lithium electrolyte with an excess of solvent, introducing suitable additives, pouring the solution onto the electrode and evaporating the excess solvent to obtain a film gel electrolyte on the electrode. To assemble an electrochromic device, a working electrode and a counter electrode coated with gel electrolyte films are interconnected and sealed around the perimeter of the device.

The content of thickening polymer in the obtained lithium electrolyte films reaches 20-35%, which leads to a relatively hard and not sufficiently sticky gel, and, accordingly, to difficulties in removing gas bubbles remaining between the electrolyte layers during the assembly of electrochromic devices.

Closest to the proposed is the technical solution described in the article [Lianyong Su, Qingyue Hong and Zuhong Lu, Journal of Materials Chemistry, 8 (1), 85-88, (1998), All solid-state electrochromic window of Prussian Blue and electrodeposited WO ₃ film with PMMA gel electrolyte], in which an electrolyte device using an electrolyte containing propylene carbonate 35%, egilen carbonate 35%, lithium perchlorate 5%, polymethyl methacrylate 25% is used in an electrochromic device. The electrolyte in the form of an opaque suspension is diluted with tetrahydrofuran, watered on a working electrode and squeezed until it connects to the counter electrode. Next, the assembled device is kept for 3 days to completely swell the polymer and form a transparent gel electrolyte layer, after which the device is sealed around the perimeter with epoxy resin. The disadvantage of the described electrochromic device is the formation of gas bubbles in the polymer electrolyte layer due to spontaneous evaporation of the volatile solvent - tetrahydrofuran.

The technical problem to which this invention is directed is to select the composition of the electrolyte, to create a method for its preparation and a method for manufacturing an electrochromic device that allows simple means to obtain an electrolyte film that does not contain gas bubbles that degrade the optical properties of the device.

The problem is solved in that the polymer electrolyte contains lithium perchlorate as a lithium salt, a mixture of propylene carbonate and ethylene carbonate as a solvent and a polymethyl methacrylate polymer in the following ratio of components: lithium perchlorate from 8 to 16 mass. %, ethylene carbonate from 20 to 30 mass. % polymethylmethacrylate polymer from 10 to 20 mass. %, propylene carbonate - the rest. As the polymethylmethacrylate polymer, for example, powder from the “Colorless plastic for prosthesis bases” kit manufactured by OJSC Stoma (Kharkov, Ukraine) is used, moreover, the solution of lithium perchlorate in the mixed solvent propylene carbonate-ethylene carbonate is thickened with polymethyl methacrylate polymer. The solution is thickened with a powdery polymer with continuous stirring until a viscous mass is formed. The resulting mass is subjected to heat treatment at a temperature of 70-100 ° C to achieve uniformity and transparency. The electrochromic device includes a working electrode of tungsten oxide deposited on a glass with an electrically conductive coating, a counter electrode of pre-restored Berlin blue (iron ferricyanide (2)), deposited on a glass with an electrically conductive coating, and a polymer electrolyte. As separators, separating the working electrode and the counter electrode, use strips of polymer tape glued to two opposite edges of one of the electrodes.

A method of manufacturing an electrochromic device includes placing a suitable portion of the thickened polymer electrolyte between the working electrode and the counter electrode, on one of which strips of the separator are applied in advance, and squeezing the electrodes until it contacts the strips of the separator, after which the excess electrolyte squeezed out of the interelectrode gap is removed. The assembled device is sealed around the perimeter using molten hot melt adhesive.

A significant difference of the proposed method is also the cathodic restoration of the counter electrode from Prussian blue just before the assembly of the electrochromic device until it is completely discolored in a lithium electrolyte that does not contain a thickening polymer.

The proposed technical solution differs from the known combination of features set forth in the claims. Analysis of a wider range of known technical solutions showed that the claimed technical solution does not follow explicitly from the prior art.

The essence of the invention is illustrated by examples.

Example 1. Preparation of lithium electrolyte

2.4 grams of anhydrous lithium perchlorate was dissolved in a mixture of 5 grams of ethylene carbonate (EC) and 9.6 grams of propylene carbonate (PC). Received 17 grams of liquid electrolyte intended for cathodic reduction of the counter electrode made from Prussian blue. To another same portion of liquid electrolyte was added 3 grams of polymethyl methacrylate (PMMA) powder from the set “Colorless plastic for prosthesis bases”, manufactured by Stoma OJSC (Kharkov, Ukraine), and stirred for 16 hours on a magnetic stirrer. An anchor of a magnetic stirrer was removed from an opaque suspension of swollen PMMA and the mixture was heated in an oven in a closed bottle for 4 hours at a temperature of 80 ° C. The mixture turned into a colorless transparent jelly - a gel (thickened) lithium electrolyte. Thus, 20 grams of an electrolyte containing 12% LiClO ₄ , 25% EC, 48% PC and 15% PMMA were obtained.

Example 2. Preparation of electrochromic electrodes

As a transparent electrically conductive material, a commercial product was used - silicate glass coated with tin dioxide doped with fluoride (K-glass) having a surface resistance of 48 Ohms / square.

The working electrodes were made by magnetron sputtering of tungsten oxide on K-glass substrates in Sibax LLC, Tomsk. The thickness of the tungsten oxide layer was 400 nm according to the manufacturer.

The counter electrodes were fabricated by cathodic deposition of Prussian blue on K-glass substrates. For this, an electrolyte was prepared containing 0.01 M potassium ferricyanide, 0.01 M ferric (III) perchlorate, 0.1 M acetic acid, 0.5 M lithium nitrate. An electrode made of K-glass and an auxiliary electrode made of stainless steel were hung in the electrolyte. At a current density of 0.05 mA / cm ² in 5 minutes, a bright blue layer of Prussian blue was deposited on a K-glass electrode. The electrode was washed with distilled water and dried in air at a temperature of 100-110 ° C for 1 hour. Immediately before the assembly of the electrochromic device, cathodic reduction (bleaching) of an electrode from Prussian blue was performed. To do this, in a special cell in a lithium electrolyte that does not contain a thickener, an electrode made of Berlin azure and an auxiliary electrode of K-glass were lowered, the electrodes were connected to a voltage source of 1.5 V and held for several minutes until the layer of Berlin azure was discolored. The electrode from Prussian blue was washed from the electrolyte with tetrahydrofuran from the outside.

Example 3. Assembly of the electrochromic device

The electrode blanks were 5x6 cm in size, on one of the short sides there were left contact pads of an electrically conductive coating of 1x5 cm in size. On the two long sides of the working electrode of tungsten oxide strips of 3x50 mm polyester tape were glued, 0.2 mm thick, as separators. The tungsten oxide electrode was wetted with a thin layer of lithium electrolyte not containing a thickener. Then, a suitable portion of the thickened electrolyte was placed in the middle of the electrode, a bleached electrode made of Prussian blue was placed on it, and the packet was slowly squeezed until the interelectrode gap was filled with electrolyte and the counter electrode touched the separator. Excess thickened electrolyte squeezed out of the gaps was removed first with a spatula and then with a swab moistened with tetrahydrofuran. Sealing the layout around the perimeter was carried out with hot melt glue using a glue gun. On opposite sides of the layout there were strips of glass with contact pads, to which wires from a voltage source were connected using clamps. The described method of assembling an electrochromic device ensures the absence of gas bubbles in the interelectrode gap.

When a voltage of 1.5 V is applied to the device (plus on the electrode from Berlin blue, minus on the electrode from tungsten oxide) it acquires a dark blue color in 2-3 minutes. When a voltage of 1.5 V reverse polarity is applied, the color brightens and reaches a pale blue in 3-4 minutes. When a voltage of 3 V is applied with the opposite polarity (minus on the electrode made of Prussian blue, plus on the electrode made of tungsten oxide), the device becomes completely colorless in 4-6 minutes. Coloring-bleaching cycles can be carried out repeatedly. Within 100 cycles, the visible characteristics of the device do not noticeably change. Longer trials are currently underway.

The above examples show that the proposed technical solution, including an electrochromic device with a lithium polymer electrolyte and a method for its manufacture, can be implemented to achieve the claimed technical result.

Claims (5)

1. An electrochromic device comprising a working electrode in the form of a film of tungsten oxide deposited on glass with an electrically conductive coating, a counter electrode in the form of a film of Prussian blue (iron ferricyanide (2)) deposited on glass with an electrically conductive coating, and a polymer electrolyte, characterized in that the polymer electrolyte has a composition, mass. %: lithium perchlorate 8-16, ethylene carbonate 20-30, polymethyl methacrylate polymer 10-20, propylene carbonate - the rest. 2. A method of manufacturing an electrochromic device according to claim 1, comprising applying an electrolyte to the working electrode and to the counter electrode, their connection, compression, and sealing of the device, characterized in that polymer strips of the separator are preliminarily applied to the opposite edges of the working electrode, then this electrode is wetted liquid electrolyte, and the counter electrode from Prussian blue is preliminarily subjected to cathodic reduction in a liquid electrolyte, then a portion of the thickened polymer el is placed between the electrodes electrolyte and squeeze them until the counter electrode is firmly in contact with the working electrode separator, after which excess electrolyte is removed and the device is sealed. 3. A method of manufacturing an electrochromic device according to claim 2, characterized in that the liquid electrolyte intended for cathodic reduction of the electrode from Prussian blue, as well as for producing a polymer electrolyte, contains lithium perchlorate, ethylene carbonate, propylene carbonate - the rest, in the following ratio of components, masses .%: lithium perchlorate 8-16, ethylene carbonate 20-30, propylene carbonate - the rest. 4. A method of manufacturing an electrochromic device according to claim 2, characterized in that during the thickening process, the polymethylmethacrylate polymer is introduced into the liquid electrolyte with continuous stirring until a viscous mass is formed, then the obtained viscous mass is subjected to heat treatment at 70-100 ° C to achieve uniformity and transparency, and then the resulting polymer electrolyte is cooled to room temperature. 5. A method of manufacturing an electrochromic device according to claim 2, characterized in that the assembled device is sealed around the perimeter using molten hot melt adhesive.