WO2019170889A1 - Method for producing electrodes on a substrate and the devices comprising said electrodes - Google Patents

Abstract

The present invention relates to a method for producing electrodes on a substrate, in particular a flexible substrate, such that said method comprises: (i) a step of depositing a gold precursor as a dispersion in a solvent or solvent mixture on said substrate; then (ii) a step of depositing a precursor of an active material as a dispersion in a solvent or solvent mixture allowing the electrochemical storage of energy, on said layer obtained in step (i); (iii) laser irradiation of the bilayer thus produced according to the desired pattern; and (iv) removal of the non-irradiated parts of the deposit by washing. The invention also relates to the devices comprising said electrodes, such as in particular micro-supercondensers.

Description

 METHOD FOR PRODUCING ELECTRODES ON A SUBSTRATE AND DEVICES COMPRISING SAID ELECTRODES

The invention aims to meet the identified needs concerning sources of electrical energy in nomadic and flexible electronic devices, such as micro-supercapacitors on flexible substrate.

 An object of the invention is to provide a method for manufacturing micro supercapacitors integrated, including flexible media, which meets the needs in terms of storage and electric power source.

 Conventional microelectronics techniques include deposition methods (physical methods such as cathodic sputtering or laser ablation, or chemical "CVD" and derivatives), and lithography, mask and etch microfabrication techniques.

 The electrodes must have the characteristics of a capacitive and / or pseudocapacitive material and good electrical percolation. The majority of capacitive and / or pseudocapacitive electrode materials are embedded on rigid and flexible substrates by electrodeposition. Even though such a method allows a control of the deposited thicknesses by adjusting the deposition time, the wet manufacturing techniques have a significant variability of the deposition conditions over time. The aging of electrolytic baths in contact with the air, the increase of impurities in suspension and the variation of the concentrations of the various elements of the bath require a regular control of the chemistry of these baths or even their replacement. All of these constraints significantly increase the manufacturing process.

Some oxides can be deposited by ALD ("atomic layer deposition"), a micro-manufacturing technique well known in the semiconductor industry. However, the thicknesses of electrodes thus manufactured are limited to a few hundred nanometers and do not allow to reach high densities of surface energy (pWh per cm ² ).

In general, the usual manufacturing processes therefore require a large number of technological steps, equipment and a heavy and expensive infrastructure. The size scales targeted (patterns above 10 micrometers) and the thicknesses of micron-sized electrodes envisioned today require alternative, less expensive methods. Direct laser writing (ELD) from metal precursors by exposure to laser radiation of high power density is a process initially developed in the microelectronics sector to meet the need for localized deposition. This technique makes it possible in particular to metallize a surface locally at a micrometric scale without altering the unexposed areas, and without resorting to techniques based on physical masks. The technique has naturally developed for the realization of conductive metal tracks (Cu, Ag, Au, ...). It was then opened to other types of materials (functional oxides, mole material, biological materials) and applications including flexible electronics.

 ELD consists of irradiating a previously deposited material in the form of a film on a substrate. It usually includes 4 main steps:

 a phase of preparation of a precursor solution. Its composition may be derived from exclusively commercial products or require a preliminary stage of chemical synthesis;

 a phase of depositing a precursor solution on the entire surface. Commonly used techniques are soaking / evaporation, spray, inkjet, or spin coating;

 a laser writing phase, on the areas to be covered with the desired pattern;

 - a final cleaning phase, which aims to eliminate residues of undecomposed precursors.

The parameter regulating mainly these phenomena is the density of energy (J.cm ² ). This will depend on the laser power density, the spot size, the scanning speed, the overlap ratio between two contiguous passages. The direct laser writing manufacturing method allows the localized deposition of thin layers of materials. The laser beam makes it possible to locally activate the deposition from a chemical precursor of the material. The precursors used are of commercial origin, deposited by the technique of spin-coating (spinette) and drop deposition. The scanning of the laser makes it possible to produce the desired patterns with a micrometric resolution.

 In addition to its rapidity, direct laser writing offers great flexibility in terms of electrode geometry, thanks to the control of the sample table by computer.

It is possible to combine steps 2 and 3, with a localized precursor deposit at the laser exposure point. More recently, the techniques "Laser induced forward transfer" (LIFT) or "Laser Direct Write Add Forward Forward Transfer" (LDW + FT) have appeared. The laser allows the transfer of material from one "donor" substrate to an "acceptor" substrate. These developments offer the possibility of making 3-dimensional patterns or transfer in mild conditions without chemical modification, such as for example the transfer of living organisms.

There is still a need to provide improved, simple, robust and inexpensive processes to provide access to high capacity integrated micro-devices that are stable during cycling and good adhesion to flexible substrates.

According to a first subject, the present invention relates to a method for producing an electrode on a substrate, said method comprising:

 (i) a step of depositing a gold precursor dispersed in a solvent on said substrate; then

 (ii) a step of depositing a precursor of an active material for the electrochemical storage of energy, said precursor being dispersed in a solvent, on said layer obtained in step (i);

 (iii) the laser irradiation of the bi-layer thus produced according to the desired pattern; and

(iv) removing the non-irradiated portions of the deposit by washing.

According to one embodiment, the method according to the invention makes it possible to promote the adhesion of active material in powder form, and thus makes it possible to deposit an active material in powder form on a substrate, in particular a flexible substrate, said substrate being devoid of conductive layer. This process is therefore distinguished from processes comprising the deposition of a gold layer on a substrate.

 According to one embodiment, the use of a gold precursor does not cause the metallization of the substrate but makes it possible to prepare a two-layer film (in particular by spin-coating), which under laser irradiation generates the growth of the material to deposit on the substrate, accompanied by the formation of gold nanoparticles that migrate into the deposit. In fact, the direct laser writing of powders does not make it possible to obtain homogeneous and adherent deposits on a polymer substrate.

 According to one embodiment, the invention therefore provides a process for preparing a bilayer comprising the active material and the gold precursor.

According to one embodiment, said substrate is an electronic insulating substrate, in particular a flexible substrate, of polyimide type. According to one embodiment, the substrate is a polyimide sheet such as a Kapton ™ sheet. The substrate may optionally comprise an intermediate layer previously deposited on said substrate. Typically, it may be a tie layer and / or a conductive layer, such as a layer of Pt, Au or Ti / Au. This layer may be deposited by evaporation, especially in the form of an interdigitated pattern, as a current collector.

 In what follows and unless otherwise indicated, the term "flexible substrate" denotes said bare substrates, as well as substrates possibly covered with such a conducting layer of Pt, Au or Ti / Au.

According to one embodiment, the film deposition of the gold precursor of step (i) may be carried out by spin-coating (or spinning), by means of a dispersion of the gold precursor in a solvent or mixture of solvents.

As a precursor of gold, there may be mentioned a gold salt, optionally hydrated, such as HAuCl ₄ .3H ₂ 0.

 As solvents, there may be mentioned THF (tetrahydrofuran), acetone, dimethylsulfoxide, dioxane, dioxolane, dimethylformamide, methyl formate, nitromethane, dichloromethane or N-methylpyrrolidone or mixtures thereof.

 According to one embodiment, the suspension of the gold precursor comprises a binder, such as cellulose, especially in the form of cellulose acetate. The cellulose acts as a binder and also makes it possible to amplify the thermal decomposition reaction of the precursor under the laser beam.

 The film typically comprises a precursor of material in the presence of a binder (for example cellulose acetate) which also acts as a thermal amplifier. The passage of the laser locally causes a thermally activated chemical reaction, which depending on the nature of the deposit involves the decomposition of the precursor, a change of oxidation state, and / or the formation of carbon-based by-products. Cellulose acetate exalts the thermal decomposition reaction.

According to one embodiment, the concentration of the gold precursor in the dispersion is between 70 and 90% (w / v, based on the weight of the precursor).

According to one embodiment, step (ii) is carried out by means of a dispersion of a precursor of active material in a solvent or mixture of solvents. As solvents suitable for the precursor dispersion of the active material, mention may be made of THF.

 As a precursor of active material, there may be mentioned in particular a metal precursor which under laser irradiation decomposes into said metal, or an oxidized metal precursor.

As active material, there may be mentioned transition metals and their oxides such as RU0 ₂ , NiO, CoO, FeOx, MnOx, ZnO, SnO ₂ , Nb ₂ 0 ₅ ; carbon and carbides such as Ti ₃ C _{2 in} particular; nitrides and carbonitrides of transition metals, where x denotes the degree of oxidation of the metal in question.

More particularly, mention may be made of transition metals and their oxides such as RU0 ₂ , NiO, CoO, FeOx, MnOx, ZnO, SnO ₂ and Nb ₂ O ₅ .

As transition metal precursors, mention may be made of the hydrated forms of the aforementioned oxides. Typically, Ru0 ₂ .1, 8 H ₂ 0 can be used as precursor of the active material.

Of the metal oxides offering such rapid oxidation-reduction mechanisms, ruthenium oxide RuO ₂ is indeed particularly interesting: It has high theoretical gravimetric capacities (1450 Fg ¹ ). Even though the cost of RuO ₂ remains high compared with other oxides, the amounts present in microelectrodes are less than 1 mg.cm ² , thus making it possible to considerably reduce the cost relative to the device surface manufactured.

As regards carbon and carbides, mention may in particular be made of the following precursors: Kuraray porous carbon YP50F, Ti ₃ C ₂ .

According to one embodiment, the film obtained in step (ii) consists of a hydrate of RuO ₂ and / or of carbon or MXenes, more particularly of a hydrate of RUO ₂

According to one embodiment, step (ii) is carried out by "spin-coating", "dip-coating" or by "spray" or drop deposition techniques by means of said dispersion.

According to one embodiment, the irradiation step (iii) is carried out by ELD of a precursor containing a metal which, under irradiation, decomposes and oxidizes or a precursor of the already oxidized metal, to the degree of oxidation allowing storage of energy through a change of oxidation state throughout the working potential window of the electrode. Typically, the irradiation can be carried out with a continuous laser with a power of less than or equal to 285 mW, for a spot size of 20-40 μm, ie a power density of less than or equal to 50 - 230 W mm ² .

 Generally the wavelength is 405 nm.

Typically, the write speed is between 0.01 mm.s ¹ and 10 mm. s ¹ .

According to step (iii), the laser writing of this two-layer of two different materials can be performed in a single laser writing step, the irradiation leading to a composite layer comprising gold and said active material , adherent to the surface of the substrate.

Step (iv) consists of washing out the undecomposed material after laser writing. The washing may typically be carried out with a solvent or a mixture of solvents, chosen from, in particular, acetone and / or ethanol.

Thus, according to the method of the invention, a homogeneous deposition of active material adhered to the substrate via the high-conductivity metal (gold) intermediate layer deposited between the substrate and the surface layer of the electrochemically strong active material is obtained .

The method according to the invention thus constitutes an alternative and simplified approach to conventional approaches generally used, to obtain high capacity and good adhesion.

 According to another subject, the present invention relates to an electrode that can be obtained according to the production method according to any one of the preceding claims, characterized in that it is composed of a bilayer mainly composed of gold, then of active material deposited on said substrate.

According to another object, the present invention also relates to the method of manufacturing an electronic micro-device comprising an electrode on a substrate, said method comprising the step of producing said electrode on said substrate according to the invention.

 As a micro-device, there may be mentioned micro-supercapacitors.

According to another object, the present invention also relates to a micro supercapacitor capable of being manufactured by the method according to the invention.

 According to one embodiment, the micro-supercapacitor comprises:

a flexible substrate; said substrate being covered with a layer of composite material comprising gold, RuO ₂ and Ru metal.

 According to one embodiment, the micro-supercapacitor comprises:

 a flexible substrate;

as a positive electrode an electrode deposited on said substrate, said electrode comprising a composite layer comprising gold, RuO ₂ and Ru metal, and

 as a negative electrode, an electrode deposited on said substrate, said electrode comprising a composite layer comprising gold and carbon.

figures

Figure 1 shows schematically the process for manufacturing micro-supercapacitors flexible laser writing Ru0 ₂ hydrated commercial. HAuCl ₄ .3H ₂ O / cellulose acetate is spin coated (1) on a bare Kapton ™ sheet, followed by RuO ₂ · xH ₂ O (2). The shaping of the film thus deposited in an interdigitated electrode pattern is then performed (3). Au / RuO ₂ deposition on Kapton ™ nu (hereinafter referred to as Kapton ™ / Au / RuO2) is then washed with acetone and ethanol (4) to reveal the energy storage device and clean the surface of all its impurities.

Figure 2 shows the diffractogram obtained for a Kapton ™ / Au / Ru0 ₂ electrode.

Figure 3 shows (A) SEM images of (A) the surface and (B) cross section of a Kapton ™ / Au / Ru0 ₂ electrode. (C) Zoom on the growth in rods in top view and (D) in transverse section on the Au adhesion layer covered with the layer of active material Ru0 ₂ .

Figure 4 (A) Voltammogram at 20 mV.s ¹ and (B) Nyquist diagram obtained for an Au / Ru0 ₂ electrode integrated on Kapton ™ without current collector.

Figure 5 illustrates the preparation of laser-interdigitated micro-supercapacitors of HAuCL and Ru0 ₂ .xH ₂ 0 on a Kapton ™ sheet. The unitary patterns have an approximate size of 1cm x 1cm.

 Figure 6 illustrates different micro-supercapacitor geometries obtained by the laser writing method. The dimensions of the patterns (diameter, width, length) are of the order of 1 cm.

Figure 7 shows (A) Voltammogram recorded at 5 mV.s ¹ and (B) Nyquist diagram obtained for a Kapton ™ integrated micro-supercapacitor. Figure 8 illustrates (A) cyclic voltammetries and (B) evolution of the capacity of the flexible supercapacitor micro at scan rates of 0.005 to 1 Vs ¹ .

 Figure 9 illustrates the capacity retention of the flexible micro-supercapacitor during 10000 cycles.

Figure 10 shows the galvanostatic charge / discharge curves obtained for a flexible Au / Ru0 ₂ micro-supercapacitor.

Figure 11 illustrates the growth of a Ru0 ₂ deposition prepared by laser writing of a HAuCl ₄ .3H ₂ O -cellulose acetate / RuO ₂ powder film. Figure 12 shows the absorbance of the HAuCI ₄ .3H ₂ 0 solution - cellulose acetate dissolved in THF. The absorbance of the energy of the laser by HAuCI ₄ · 3H ₂ 0 explains the key role of this compound in the production of electrodes adherent to the surface of the flexible substrate.

Examples

The deposition of the precursors was carried out by the spin-coating technique. The laser engraving was carried out with the Dilase 250 equipment marketed by KLOE. The base is a laser lithography bench usually used for insolation of resins, but with an optical line adapted to the needs of laser writing (lambda = 405 nm and power of 0.285W), an alignment module to realize successive deposits of materials, a sample table with a controlled movement. The control software includes the ability to create drawings via the integrated software, or import them after definitions from microelectronics design software (GDS format ...).

Example 1 (Comparative) Deposition of a monolayer on a Kapton ™ flexible substrate previously covered with a current collector (Au / Ti / Kapton ™)

The ruthenium of commercial origin, that is to say the Ru0 ₂ × xH ₂ O powder from Sigma Aldrich, is deposited directly in its oxidized Ru (+ IV) form on the polymer ,. The size of RuO ₂ particles is estimated at 0.2 μm by dynamic light scattering (DLS). ATG analyzes made it possible to estimate the composition at Ru0 ₂ .1, 8H ₂ 0.

The method for manufacturing the flexible electrodes is as follows: 15 mg of RuO ₂ .1, 8H ₂ O are dispersed under ultrasound for 10 min in 0.5 mL of a mixture of cellulose acetate / THF (Ru / cellulose acetate ratio) set at 60% by mass) then spun on Kapton ™ / Ti / Au (500 "rpm", 30s). The ELD of the film is then made, and the parts that are not exposed to the laser are removed during an acetone wash and ethanol. It turns out that the deposit is very inhomogeneous and sparse, testifying to the poor adhesion of the deposit on the flexible support.

Example 2 Laser Writing (ELD) of the Kapton Film Bilayer Previously Coated with an Au / Ti / Polyimide Conductive Interdigit Pattern (with a Tie Layer)

/ current collector)

A Kapton ™ / Ti / Au / Ru0 ₂ electrode is prepared by laser writing of a film obtained by spin coating a solution of HAuCl ₄ .3H ₂ O / cellulose acetate / THF followed by a coating of a solution of RuO ₂ .xH ₂ O / THF on a Kapton ™ substrate covered with a Ti / Au collector (deposited by evaporation). This one delivers a capacity of 414 mF.cm ² .

The bilayer is made on a Kapton film previously covered with an interdigitated Au / Ti / polyimide pattern:

The deposition in spin-coating (spinning) of the two layers is carried out in two steps: initially, 27 mg of HAuCl ₄ .3H ₂ O (Sigma Aldrich) are dispersed in 0.5 mL of cellulose acetate / THF mixture , then sputtered (thickness 2.4 ± 0.6 μm according to the profilometer measurements). Then, in a second step, 15 mg of RUO ₂ .XH ₂ 0 are ultrasonically dispersed in 0.5 mL of THF, and are in turn deposited by spin-coating and drop deposit. The spin-coating parameters are: rotation at a speed of 500 "rpm" for 30s, and an acceleration of 500 "rpm" .s ¹ ). The thickness of the deposited film is estimated at 55 ± 5 μm under a 3D microscope). At this stage, the amount of RuO ₂ present in the film is determined by "ICP" assay of ruthenium. A mass content of 2.05 mg.cm ² is obtained.

The ELD of the film is performed at a power of 182 mW and a write speed of 1 mm. s ¹ . Optical microscopic observation of the electrode prepared from the precursor bilayer (Au and RuO ₂ ) reveals that the deposition is homogeneous and dense in comparison with that obtained previously (Example 1) without the HAUCI precursor layer ₄ . 3H ₂ 0 in cellulose acetate. This confirms that the introduction of the gold salt in the formulation of the electrode therefore allows a better grip of the electroactive material, and leads to more homogeneous electrodes. The nature of the electrode is verified by XRD. After being freed from the intense peaks relative to the Ti / Au current collector located at 38.5 °, the diffraction peaks of Ru0 _{2 are} observed (quadratic structure P / 42 nm, JCPDS 00-021-1 172). In addition, no peak relative to the HAuCl ₄ .3H ₂ 0 is visible, showing the reduction of salt in Au (0). The deposit obtained after ELD includes both Au and Ru0 ₂ . The observation of the surface obtained by scanning electron microscopy of a flexible Au / RuO ₂ electrode reveals that the surface is organized in the form of a "forest" cluster with a "tree" growth containing ruthenium (d after the "EDX" analyzes) Such a structure is favorable to the faradic reactions of surfaces involved in the RuO ₂ energy storage process.

Example 3 Deposition of Au and Deposition of RuO 3 on bare substrate

It is made according to Example 2 from an uncoated Kapton ™ substrate.

 The electrodes obtained are evaluated as follows:

The electrochemical behavior of the Au / RuO ₂ flexible electrodes is then evaluated in a three-electrode cell by cyclic voltammetry and impedance spectroscopy in 1 MH ₂ SO ₄ medium. On the voltammogram recorded at 20 mV.s ¹ , it is observed that the current delivered by the substrate (represented by diamonds) is negligible, and that the electrochemical signature of Ru0 ₂ is clearly identifiable, with however a limitation of the anodic current to the potentials. negative. The capacitive behavior of the electrode is confirmed by electrochemical impedance spectroscopy. On the Nyquist diagram obtained at the quiescent potential ("EOCV" = +0.185 V), we observe a vertical line at low frequencies, characteristic of a capacitive behavior of the electrode. We also note the absence of a semicircle for the high frequencies, showing the good conduction properties of electrons in the Au / Ru0 ₂ layer. The equivalent series resistance (ESR) is only 0.2 Q.cm ^-2 . Therefore, the flexible electrode demonstrates very interesting power performance despite the faradic nature of the storage mechanisms involved, with 60% of the initial capacity delivered during a discharge of 1 s (scanning speed of 1 Vs ¹ ).

According to the voltammogram obtained, the capacity of the electrode is maximum at 0V vs Hg / Hg ₂ S0 ₄ . Since the addition of gold salt makes it possible to hang more Ru0 ₂ during the writing, it is expected that the amount of HAuCI ₄ .3H ₂ O affects the amount of RuO ₂ deposited, and therefore on the surface capacitance of the flexible electrodes delivered. Thus, different masses of HAuCl ₄ .3H ₂ O are dispersed in 0.5 mL of the cellulose acetate / THF mixture and spun onto the substrate. The concentrations used are 14, 30, 60 and 120 mg.mL-1 (the deposit no longer adheres to more than 120 mg.mL-1). A fixed mass of 15 mg of commercial RuO ₂ is dispersed in 0.5 mL of THF and deposited in turn (same protocol as before). The writing parameters are set at P = 55 mW and v = 3 mm. s ¹ for the sake of comparison. The electrodes thus prepared are then tested in H ₂ S0 ₄ medium by cyclic voltammetry in a three-electrode configuration. On voltammograms obtained at 20 mV.s ¹ for the four electrodes, it is noted that regardless of the gold salt content of the deposited film, the RuO ₂ signature is retained. However, a significant increase in capacitive current is observed for a gold salt content of 80% by weight (mixture of gold salt and cellulose acetate). To understand this increase in capacity, four electrodes are prepared with the same gold salt content of the films deposited by spin-coating, but without introduction of Ru0 ₂ .xH ₂ 0. The capacity delivered by the electrodes is then taken under the same conditions

The capacities delivered by the electrodes not containing Ru0 ₂ are very low and increase slightly with the amount of gold salt deposited by spin-coating (from 3.7 mF.cm ² for a concentration of 14 mg.mL ¹ to 7.3 mF.cm ² for 120 mg.mL ¹ ). The capacities recorded for Au / Ru0 ₂ electrodes (solid symbols) are conversely very high (from 122 mF.cm ² to 414 mF.cm ² ). In addition, the capacity values delivered are very similar for gold salt contents ranging from 32% by mass to 67% by mass, while a sharp increase is observed for a content of 80% by mass (more than three times the recorded capacity at lower gold salt contents). The optical microscope images reveal a denser surface / deposit, which reinforces the previous observations concerning the increase of the adhesion of RU0 ₂ in the presence of HAuCl ₄ .3H ₂ 0.

To be able to conclude on this sudden increase in the capacity delivered, the quantification of the RuO ₂ present in the electrodes after writing is carried out by "ICP" assay of the ruthenium. Thus, it is noted that the amount of RuO ₂ varies little for gold salt contents of less than 67% by weight (from 40 to 55 pg.cm ² of electrode) and increases drastically when 80% by mass of HAuCl ₄ .3H ₂ 0 are introduced (277 pg.cm ^2, or 5 times). A gold salt concentration of 120 mg.mL ¹ therefore makes it possible to deposit more Ru0 ₂ during the writing step.

The advantage of the method of manufacturing by laser writing according to the invention lies in the fact of being able to integrate Ru0 ₂ commercially available directly on flexible polyimide substrate with a Ti / Au layer obtained by physical evaporation. The performances are superior to those obtained until now in "LSG" / RU0 ₂ with an ELD methodology. In the next step, the evolved Ti / Au intermediate metal layer was removed and the entire Kapton ™ ELD deposition process was optimized.

Example 4: Laser etching (ELD) of the two-layer deposition on Kapton ™ bare film (without current collector)

An optimum gold salt content of 80% by mass achieves a high surface area capacity of 414 mF.crrr ² . Thus, it is this electrode formulation that is retained for the manufacture of flexible micro-supercapacitors directly on Kapton (detailed in Figure 1). As before, 60 mg of HAuCl ₄ .3H ₂ O are dispersed in 0.5 mL of a cellulose acetate / THF mixture, while 15 mg of RUO ₂ .1, 8H ₂ 0 are ultrasonically dispersed for 10 min. 0.5 mL of THF. Then, the solutions are successively deposited on Kapton ™ (gold precursor by spin and spin / drop for Ru0 ₂ .1, 8H ₂ 0).

A square pattern of 5mm x 5mm is first made to verify the properties of the integrated Kapton ™ electrode material without Ti / Au collector. X-ray diffraction analysis (FIG. 2) again reveals the presence of crystalline RuO ₂ (P42 / mnm, JCPDS No. 00-043-1027) as well as crystalline Au (Fm3m, JCPDS No. 03- 065-2870) in the electrode. Furthermore, the presence of ruthenium metal (P63 / mmc, JCPDS No. 03-065-1863) is also noted by comparison with an AU / RU0 ₂ electrode integrated on KaptonTM / Ti / Au.

The surface of the Au / RuO ₂ electrode is observed under a scanning electron microscope (FIG. 3A). The deposit is conformal and highly rough over the entire surface of the substrate, and comprises growths of Ru0 ₂ (in the form of "trees") (Figure 3C) resting on rods (Figure 3A, B, C). A section perpendicular to the substrate (by "FIB") makes it possible to specify the vertical structure of the deposit. Three distinct layers are formed:

 a first layer containing granular gold and Ru particles with a thickness of 35 ± 5 nm.

A second layer of RuO ₂ , in the form of nano-rods perpendicular to the surface of average diameter 40-60 nm and height of between 200 and 450 nm. Some gold nanoparticles are scattered.

- A third layer comprising excrescences of Ru0 ₂ , with a high porosity.

The interface between the first two layers is steep and compact giving the impression of RuQ ₂ nano-stick growth directly on the layer Golden. The upper interface with the superficial layer of excrescences gives the impression of a layer of Ru0 ₂ redeposited with a weak "connection". In addition, there is a migration of Au nanoparticles in rod structures during growth (Figure 3D).

As shown in FIG. 11, the deposit increases in the form of crystals (A) from the polyimide substrate (B) in a first porous layer and a second, denser layer (C), both containing gold under form of nanoparticles (D). Note that the substrate is not metallized (absence of gold layer), but is covered with a layer of Ru / Ru0 ₂ (E and F).

The combination of HAuCI ₄ .3H ₂ 0 salt and cellulose acetate makes it possible to optimize the absorption of the energy provided by the laser, and the diffusion of this energy by combustion of the acetate within the deposit. In fact, FIG. 12 illustrates that the absorbance of the THF and THF solutions containing the cellulose acetate is zero at the wavelength of the laser used (405 nm), while the addition of HAuCI ₄ .3H ₂ 0 increases the absorbance, with or without cellulose acetate.

Regarding the role of cellulose acetate, simulations were performed with Comsol Multiphysics software. A polyimide substrate is covered with a layer of HAuCl ₄ .3H ₂ O + cellulose acetate. The evolution of the temperature during the passage of the laser for a power of 285 mW and a writing speed of 5 mm. s ¹ is modeled (at t = 3.6 ms). It is noted that the temperature is above 200 ° C (decomposition temperature of HAuCl ₄ .3H ₂ 0 salt) on 50 pm on either side of the passage of the laser. Thus, cellulose acetate optimizes the diffusion of heat within the deposit, which ultimately promotes the adhesion of the active material to be deposited by forming particles of Au and Ru.

The electrochemical behavior of an Au / RuO ₂ electrode without current collector is also evaluated by cyclic voltammetry and impedance spectroscopy in a medium with 1 MH ₂ SO ₄ . The electrochemical signature is conserved (Figure 4A). The capacity delivered is limited to 61 mF.cm ² against 414 mF.cm ² (in the presence of the current collector Au / Ti) at a scanning speed of 20mV.s ¹ . This reduction in capacity is attributed to an increase in the resistance caused by the absence of an underlying current collector in this example, which can be optimized later. This increase in resistance is confirmed by the Nyquist diagram presented in Figure 4B. Indeed, the capacitive behavior observed at low frequencies is preserved, while a semicircle is clearly visible at high frequencies, characteristic of an increase in the resistance of the electrode. Optimization of the electrical contact of the microsystem should make it possible to minimize the effective equivalent series resistance of the device.

Example 5 Preparation of a Micro-Supercapacitor

After confirming the capacitive behavior of the Au / Ru0 ₂ electrodes on Kapton ™, laser writing of micro-supercapacitors is performed. Figure 5 is a photograph of a Kapton ™ sheet on which 36 micro supercapacitors of AU / RU0 ₂ have been manufactured. The manufacturing method proposed here thus offers the possibility of preparing about 40 flexible micro-supercapacitors on a Kapton ™ disk 10.16 cm in diameter.

 In addition, the KIoéDesign software, used to define the pattern of the device, makes it possible to prepare micro-supercapacitors of various patterns (control of the size of interdigital fingers, concentric electrodes ...) as shown in the photograph shown in Figure 6.

The performances of a micro-supercapacitor with interdigital electrodes are then evaluated in 1 MH ₂ S0 ₄ medium. The two polarities of the device are composed of 4 fingers of length I = 5 mm, width L = 500 μm, and separated by an inter-space i = 500 μm. The voltammogram obtained for this flexible micro-supercapacitor (symmetrical cell) is presented in FIG. 7A.

The resulting curve is quasi-rectangular, confirming the pseudo capacitive storage of energy. The deviation from the ideal behavior observed at the beginning of the discharge is explained by the anodic limitation observed in three-electrode configuration at negative potentials. The micro-supercapacitor delivers a capacity of 27 mF.cm ² , twice as much as the capacity delivered by a micro-supercapacitor prepared by laser engraving GO / RuCI ₃ . Two distinct areas are again visible on the Nyquist diagram based on the impedance values collected by EIS (Figure 7B), with a vertical line obtained at low frequencies, and a half circle for high frequencies. The diameter of the latter is about 6 Q.cm ² and reflects a contact resistance due to the absence of Ti / Au collectors on the device. The equivalent series resistance is 12 Q.cm ² . This value is the same an order of magnitude than that obtained for Ru0 ₂ micro-supercapacitors integrated on silicon by Ru electroplating on carbon nanostructures.

The power capabilities of the flexible micro-supercapacitor are studied through cyclic voltammetry tests carried out at several scanning speeds over a potential range of 1 V. Figure 8A groups recorded voltammograms at scanning speeds of 20 mV.s. ¹ to 1 Vs ¹ . Note that the form of the voltammogram obtained at 20 mV.s ¹ has the signature typically pseudocapacitve expected for Ru0 ₂ . For a higher speed of 100 mV.s ¹ , there is a signal distortion due to a more resistive behavior of the device. This limitation is even more marked for the voltammograms recorded at 0.5 and 1 Vs ¹ . The capacity delivered by the flexible micro-supercapacitor is calculated for each scanning speed, then reported in Figure 8B. As expected from the analysis of the cyclic voltammetry curves, the capacitance of the device decreases sharply as the scanning speed increases, reaching 16% of the initial capacity for a discharge time of 1 s. The power capacity retention is unsatisfactory compared to that of the carbon-based micro-supercapacitors (eg, 73% capacity retention at 10 times higher current density for micro GER supercapacitors). Nevertheless, the faradic nature of the energy storage mechanisms involved here limits the power densities provided by the device. The cyclability of the micro-supercapacitors thus prepared is checked on 10

000 cycles of cyclic voltammetry carried out on a window of potential of 1 V with 100 mV.s-1.

The capacity is normalized to the capacity delivered during the first cycle, and reported every 500 cycles in Figure 9. Thus, the capacity decreases rapidly and reaches 85% of the initial capacity during the first 1000 cycles, then stabilizes during the rest from experience, with a capacity retention of 78% to 10000 cycles. This decrease of 15% in the first cycles is attributed to the surface loss of RuO ₂ grains which adhere less to the electrode.

The flexible micro-supercapacitor is also subjected to galvanostatic charge / discharge tests (Figure 10). A triangular signal is observed for current densities of 0.16 mA.cm ² at 3 mA.cm ² , characteristic for a supercapacitor. In addition, an increase in the slope is observed when the current density is higher, confirming the significant decrease in capacity for faster discharges observed during cyclic voltammetry tests. The ohmic drop is manifested by a drop in cell voltage at the beginning of charge and discharge, increases from 7 mV at 0.16 mA.cm ² to 139 mV at 3 mA.cm ² , thus revealing an ESR of 45 Q.cm ² - the deviation from the value of 12 Q. Impedance-determined cm ² is due to aging of the micro-supercapacitor during cycling tests as well as sampling time.

An integrated micro-supercapacity was therefore prepared by the laser writing technique directly on the Kapton ™, which has a capacity of 27 mF.cm ² to 5 mV.s ¹ in medium 1 MH ₂ S0 ₄ , surpassing most micro-supercapacitors integrated on a flexible substrate. This has good stability of performance during cycling (tested up to 10,000).

Claims

A method of producing an electrode on a substrate, said method comprising: (i) a step of depositing a gold precursor dispersed in a solvent or solvent mixture on said substrate; then  (ii) a step of depositing a precursor of an active material dispersed in a solvent or mixture of solvents for the electrochemical storage of energy, on said layer obtained in step (i);  (iii) the laser irradiation of the bi-layer thus produced according to the desired pattern; and (iv) removing the non-irradiated portions of the deposit by washing. 2. The method of claim 1, wherein the precursor of the active material is a precursor of the oxidized metal or a precursor containing a metal salt which under irradiation decomposes. 3. Method according to claim 1 or 2 such that the active material is selected from transition metals and their oxides such as Ru0 ₂ , NiO, CoO, FeOx, MnOx, ZnO, SnO ₂ , Nb ₂ 0 ₅ ; carbon and carbides; nitrides and carbonitrides of transition metals; where x denotes the degree of oxidation of the metal in question. The method of any of the preceding claims, wherein the substrate is a polyimide sheet. 5. Method according to any one of the preceding claims, such as the step (i) is carried out by "spin-coating" by means of a dispersion of HAuCl ₄ .3H ₂ O in a solvent or solvent mixture and comprising at least one cellulosic compound. 6. Method according to any one of the preceding claims, such as the step (ii) is carried out by means of a dispersion of the precursor of active material in a solvent or mixture of solvents. 7. Electrode obtainable according to the production method according to any one of the preceding claims, characterized in that it is composed of a bilayer mainly composed of gold, then of active material, deposited on said substrate. 8. A method of manufacturing an electronic micro-device comprising the method of developing an electrode according to any one of the preceding claims. Micro-supercapacitor capable of being manufactured by the process according to claim 8. An ultracapacitor according to claim 9 comprising:  a flexible substrate; said substrate being covered with a layer of composite material comprising gold, RuO ₂ and Ru metal.