THERMAL TEMPERING OF A WORKING ELECTRODE

Abstract

A cathodic subassembly for an electrochromic system, suitable for being deposited on top of a substrate having a glass function, includes a first transparent conductive layer, and a working electrode, arranged on top of the first transparent conductive layer, wherein the working electrode is suitable, by virtue of its chemical composition, for being functional after thermal tempering.

Claims

1. A cathodic subassembly for an electrochromic system, said cathodic subassembly being suitable for being deposited on top of a substrate having a glass function, and comprising: a first transparent conductive layer, and a working electrode, arranged on top of said first transparent conductive layer, wherein said working electrode, is suitable, by virtue of its chemical composition, for being functional after thermal tempering, and wherein said working electrode is at least composed of a tungsten oxide (WOx) doped with at least one transition metal element Y chosen from the group comprising niobium (Nb), molybdenum (Mo), vanadium (Va), tantalum (Ta), titanium (Ti), nickel (Ni), zinc (Zn) and zirconium (Zr).

2. The cathodic subassembly as claimed in claim 1, wherein said at least one transition metal element Y is present according to a ratio Y/(Y+W), relative to the tungsten element (W), of greater than or equal to 2 at. %, and/or less than or equal to 30 at. %.

3. A process for manufacturing a cathodic subassembly as claimed in claim 1 on a substrate having a glass function, said process comprising depositing by magnetron, with at least one deposition station equipped with one or more targets suitable for the magnetron deposition, said working electrode on top of the first transparent conductive layer.

4. The manufacturing method as claimed in claim 3, wherein the working electrode is deposited by magnetron deposition at a temperature of less than 180° C.

5. The manufacturing process as claimed in claim 3, wherein edges of said substrate are ground before and/or after the deposition of said working electrode.

6. An electrochromic system suitable for being deposited on top of a substrate having a glass function, and comprising: a cathodic subassembly as claimed in claim 1, a counterelectrode arranged on top of said cathodic subassembly, a second transparent conductive layer arranged on top of said counterelectrode, lithium ions introduced into said electrochromic system, and optionally a distinct layer of an ion conductor inserted between the working electrode and the counterelectrode.

7. An electrochromic system suitable for being deposited on top of a substrate having a glass function, and comprising: a second transparent conductive layer arranged on top of said substrate, a counterelectrode arranged on top of said second transparent conductive layer, a cathodic subassembly as claimed in claim 1, arranged on top of said counterelectrode, lithium ions introduced into said electrochromic system, and optionally a distinct layer of an ion conductor inserted between the working electrode and the counterelectrode.

8. The electrochromic system as claimed in claim 6, wherein said counterelectrode is at least composed of a nickel-tungsten oxide (NiWxOz).

9. The electrochromic system as claimed in claim 6, wherein: a thickness of the working electrode is between 100 and 1500 nm, and/or a thickness of the counterelectrode is between 100 and 1500 nm.

10. A process comprising manufacturing an electrochromic system as claimed in claim 6 on a substrate having a glass function.

11. A method comprising thermal tempering of a cathodic subassembly as claimed in claim 1, arranged on top of a substrate having a glass function.

12. The method as claimed in claim 11, wherein the thermal tempering is carried out on a cathodic subassembly and a substrate not having been annealed beforehand.

13. A tempered electrochromic system obtained after a thermal tempering as claimed in claim 11.

14. A glazing incorporating a tempered electrochromic system as claimed in claim 13, said glazing being suitable for use as glazing of a building, or as glazing equipping internal partitions or windows of a transportation vehicle.

15. The manufacturing method as claimed in claim 4, wherein the temperature is less than 160° C.

16. The manufacturing method as claimed in claim 15, wherein the temperature is less than 140° C.

17. The electrochromic system as claimed in claim 8, wherein the nickel-tungsten oxide (NiWxOz) is doped with at least one transition metal element.

18. A method comprising thermal tempering of a cathodic subassembly, arranged on top of a substrate having a glass function, the cathodic subsassembly being incorporated in an electrochromic system as claimed in claim 6.

19. The glazing as claimed in claim 14, wherein the glazing of the building is an exterior glazing of an internal partition or glazed door.

20. The glazing as claimed in claim 14, wherein the transportation vehicle is a train, an airplane, an automobile or a boat.

Description

[0065] Other characteristics and advantages of the invention will emerge on reading the following description of particular embodiments, given by way of simple illustrative and nonlimiting examples, and of the appended figures, among which:

[0066] FIG. 1 is a schematic representation of an electrochromic system according to one particular embodiment of the invention.

[0067] FIG. 2 is a flow diagram illustrating the successive steps of a thermal tempering process according to the invention.

[0068] In the various figures, unless otherwise indicated, the reference numbers that are identical represent similar or identical elements.

[0069] The various elements illustrated by the figures are not necessarily represented in true scale, the emphasis being more on the representation of the general operation of the invention.

[0070] Several particular embodiments of the invention are subsequently presented. It is understood that the present invention is in no way limited by these particular embodiments and that other embodiments may perfectly well be implemented.

[0071] According to one particular embodiment, and as illustrated by FIG. 1, the invention relates to an electrochromic system (8) deposited on a substrate (1) having a glass function and comprising, in their order of deposition: an indium tin oxide (ITO) first transparent conductive layer (2A), a doped tungsten oxide (WOx) working electrode (3), a silica (SiO.sub.2) electrolyte (4), a nickel-tungsten oxide (NiWO) counterelectrode (5), and an indium tin oxide (ITO) second transparent conductive layer (2B).

[0072] It should be noted that lithium (Li) ions have at this stage already been introduced into said electrochromic system by deposition of two distinct layers of lithium, the first between the working electrode and the electrolyte, the second between the counterelectrode and the second transparent conductive layer, each deposition being followed by a heating step in order to bring about diffusion of the lithium ions in the electrochromic stack.

[0073] According to one particular embodiment, at least a part and preferentially all of the layers forming the electrochromic stack are deposited by magnetron deposition. According to an alternative embodiment, at least a part of these layers is deposited according to an alternative process, for example via a liquid deposition.

[0074] According to an alternative embodiment not illustrated, the order of deposition of the electrochromic stack on the substrate is reversed, so that it has, in the following order of deposition: an indium tin oxide (ITO) first transparent conductive layer (2A), a nickel-tungsten oxide (NiWO) counterelectrode (5), a silica (SiO.sub.2) electrolyte (4), a doped tungsten oxide (WOx) working electrode (3), and a second transparent conductive layer (2B) also made of indium tin oxide (ITO). The working electrode is then deposited on top of the counterelectrode.

[0075] According to these alternative embodiments, the first transparent conductive layer and the working electrode form a cathodic subassembly (6), while the counterelectrode and the second transparent conductive layer form an anodic subassembly (7).

[0076] Once the electrochromic system 8 has been deposited on the substrate 1, the assembly is thermally tempered, as illustrated by FIG. 2, by heating at a high heat up to the softening point of the glass, typically at a temperature greater than 600° C., for 5 minutes, then by abrupt cooling of the assembly, for example by jets of air and/or of inert gas. The tempered electrochromic system 8* obtained then has an increased hardness.

[0077] The experimental protocol described below makes it possible to bring to the fore some of the technical advantages conferred by a cathodic subassembly (6) according to the invention, without however limiting the scope of the claims.

[0078] The objective of the tests is to evaluate the thermal tempering resistance performance results of various cathodic subassemblies, as a function of their chemical composition.

[0079] To do this, four samples are prepared, including a first sample which has a composition known from the prior art and serves as a comparative reference, and three samples which relate to three particular embodiments of the invention using tungsten oxide (WOx) working electrodes, respectively doped with 10% atomic mass of niobium (Nb) (sample No. 2), molybdenum (Mo) (sample No. 3) and vanadium (V) (sample No. 4). Each of the four samples is prepared according to the same protocol. The substrate is a glass 2 mm thick. It is first cleaned in order to remove from it any dust that might compromise the correct operation of the electrochromic stack. The substrate is then placed on a carrier that will pass through a deposition line. All the materials are deposited by magnetron sputtering. Within the deposition line, 400 nm of ITO 2A followed by 380 nm of tungsten oxide (doped or non-doped) 3 are deposited on the heated substrate 2 at a temperature of 240° C. The doped working electrodes are deposited from a doped target. The amount of doping is given by the supplier, and is subsequently verified by microanalysis on the sample. Lithium is then deposited in its metal form on the cathodic subassembly 6 thus formed, until the light transmission of the sample at 800 nm, measured using a spectrometer incorporated within the line, is between 5% and 50%. Finally, the sample is tempered conventionally by subjecting it to heating at ˜650° C. for 5 min, before being cooling in ambient air.

[0080] Measurement of the Reversibility Range:

[0081] Before beginning the capacity or contrast measurements, it is necessary to determine the measurement range suitable for the sample tested. To do this, two series of cyclic voltammetry are carried out in order to determine the voltage range beyond which the sample is no longer reversible. A cyclic voltammetry (CV) consists in applying a voltage gradient with a defined speed (in this case 2 mV/s) between two voltage values, and in measuring the current thus created.

[0082] The first series consists in performing 10 (ten) cycles between the voltage V0 noted at time 0, when the sample is connected and the circuit is open (resting potential), and a first voltage V1 greater than V0, then in repeating the operation with increasing values of voltage V1, following an incremental step of 0.1 V.

[0083] The second series consists in performing the same operation between V0 and V2 with V2 being less than V0 and V2 ranging toward increasing low voltages. For each series of 10 (ten) cycles, it is considered that the reaction is reversible as long as the difference in total charge exchanged between the 5th and 10th cycle differs by less than 15%. By continuing to increase the value of V1 (respectively decrease the value of V2), the voltage threshold V1m (respectively V2m) beyond which the sample is no longer reversible is finally found. [V2m: V1m] is then the measurement range for this sample.

[0084] Capacity Measurements

[0085] In order to measure the capacity of the cathodic subassemblies tested, electrochemical measurements in a three-electrode assembly are carried out. The electrodes bathe in a liquid electrolyte consisting of a solution containing 1 mol of lithium perchlorate diluted in anhydrous propylene carbonate. The cathodic subassembly studied is electrically connected to ultrasound by virtue of a weld, before being immersed in the electrolyte. This sample cathodic subassembly then acts as working electrode of the three-electrode measurement system, while clean pieces of lithium metal act as working electrode and counterelectrode. The voltage measured is the difference in potential between the sample tested and the reference electrode (in this case Li metal), while the voltage or the current is applied during the experiment between the sample tested and the counterelectrode (in this case another piece of Li metal).

[0086] To measure the electrochemical capacity of a sample, chronopotentiometry operations are carried out. Chronopotentiometry (CP) consists in applying a constant current (in this case 13.4 mA/cm.sup.2) and in measuring the voltage at the terminals of the sample and of the counterelectrode. When V1m or V2m is reached, the operation is repeated with a current of the opposite sign. Such a cycle is reproduced 20 (twenty) times. The charge capacity is then obtained from the 20th cycle, by integrating the current applied relative to the time of a half cycle.

[0087] Contrast Measurements

[0088] The contrast is measured on a complete stack. In this case, the measurement is carried out in a two-electrode assembly: the ITO layer directly in contact with the working electrode constitutes the cathodic subassembly, while the ITO layer directly in contact with the counterelectrode constitutes the anodic subassembly, which acts both as reference electrode and as counterelectrode of the electrochemical system studied. The protocol enabling the stability zone of the system to be determined can be applied in the same way as described above.

[0089] In order to measure the contrast of a complete stack, 20 (twenty) chronoamperometry operations are carried out with simultaneous measurement of the total light transmission. The latter can be done by coupling the electrochemical measurement to a spectrometer. Chronoamperometry (CA) consists in applying a constant voltage and in measuring the current thus created. In this case, 20 (twenty) CA operations are carried out between V1m and V2m. The voltage application duration is chosen such that the current measured at the end of each step changes by less than 0.2 μA/cm.sup.2/min. During the 20th cycle, the minimum light transmission LTmin and the maximum light transmission LTmax are recorded. The contrast is then defined as the ratio LTmax/LTmin.

[0090] The results obtained are given in table 1 below:

TABLE-US-00001 TABLE 1 Composition of the sample Capacity (mC/cm.sup.2) Sample No. 1 60 Sample No. 1 after tempering 5 Sample No. 2 40 Sample No. 2 after tempering 35 Sample No. 3 75 Sample No. 3 after tempering 33 Sample No. 4 64.6 Sample No. 4 after tempering 20.6

[0091] The results obtained and presented in table 1 make it possible first to demonstrate the improvement in the capacity value measured after tempering for samples 2 to 4, in comparison with the value measured for sample 1.

[0092] The highest capacity for a tempered sample is that obtained from sample No. 2, doped with 10% atomic mass of niobium (Nb). Sample No. 2 thus has the most advantageous composition for resisting thermal tempering.

[0093] Additional analyses carried out by X-ray spectroscopy reveal in particular that within the context of the tungsten oxide working electrodes doped, respectively, with niobium (Nb), molybdenum (Mo) or vanadium (V), electrodes that are functional after tempering differ from the known electrodes, not functional after tempering, on the one hand through the absence or virtual absence of crystalline Li.sub.2W.sub.2O.sub.7 and/or of crystalline Li.sub.2WO.sub.4, which significantly harm the operation thereof, and on the other hand through the presence of Li.sub.2W.sub.5O.sub.16.

[0094] Although particular embodiments of the present invention have been illustrated and described, it is obvious that various other changes and modifications can be made within the spirit and scope of the invention. The present text is thus intended to cover, in the appended claims, all the modifications which are within the context of the present invention.