EP4453975A2

EP4453975A2 - Coupled etching and deposition process and capacitor foil formed by the process

Info

Publication number: EP4453975A2
Application number: EP22822115.6A
Authority: EP
Inventors: Cristiano BACCO; Erkan Küzeci
Original assignee: TDK Electronics AG
Current assignee: TDK Electronics AG
Priority date: 2021-12-23
Filing date: 2022-11-25
Publication date: 2024-10-30
Also published as: WO2023117299A3; WO2023117299A2; DE102021134524A1

Abstract

The present application addresses a coupled etching and deposition process and a capacitor foil formed by the process. According to the coupled etching and deposition process an anodic reaction is coupled to a cathodic reaction, such that in the anodic reaction a first foil containing a metal is electrochemically etched in an electrolyte whereby ions of the metal are dissolved into the electrolyte and whereby in the cathodic reaction ions of the metal from the electrolyte are deposited on a second foil.

Description

Coupled etching and deposition process

The present invention addresses a coupled etching and deposition process and a capacitor foil formed by the process .

Electrochemical etching of capacitor foils , in particular of aluminum foils , is a well-established technique in the field of producing capacitor structures , in particular for creating high surface area capacitor foils for coiled capacitors .

Other examples in which etching is used to produce patterns , surface enhancement , or nano-structuring are , for example , titanium foils or titanium platelets .

The patent application US 2015/ 0062782 Al discloses that aluminum structures can be deposited from ionic liquid solutions electrochemically . This galvanic deposition approach is suggested as an alternative to etching . However, a highly pure aluminum ion source is required .

In the classical electrochemical etching of aluminum foils , however, aluminum ions are dissolved into the electrolyte and may be lost or are at least highly diluted .

The above problems are at least partially solved by a process according to the present disclosure and by a foil according to the present disclosure .

According to a first aspect a coupled etching and deposition process is provided in which an anodic reaction is coupled to a cathodic reaction such that in the anodic reaction a first foil containing a metal is electrochemically etched in an electrolyte whereby ions of the metal are dissolved in the electrolyte and whereby in the cathodic reaction ions of the metal from the electrolyte are deposited on a second foil as a cathode , which may be an already etched foil . In the coupled etching and deposition process both the first foil and the second foil have contact to the same electrolyte .

The anodic reaction is a first hal f-cell reaction at an anode in which the foil or alternatively a metal platelet is etched by which the metal becomes partly dissolved and ions are formed in the electrolyte .

The cathodic reaction is a second hal f-cell reaction in which at a cathode ions of the metal become reduced and metal is deposited on the cathode .

Thereby the above concept allows for direct recovery of metal from the electrolyte . Thereby loss of the metal from throwing away the electrolyte or the necessity of recovering aluminum in a separate process may be avoided . Separate recovery processes often only create low grade purity aluminum .

On the other hand, the high purity metal foil that is etched in the anodic reaction may act as a metal source .

The inventors of the present invention have found out that the ions of the metal which are electrochemically produced during the etching in an anodic reaction may serve as a source for deposition onto a second metal foil , preferably an etched aluminum foil . The process is particularly preferred for aluminum foils .

In the case of aluminum foils the etched or nanostructured foil may suf fer up to 30% weight loss of the material in an anodic etching reaction . Accordingly, the above-proposed concept allows to at least partially recover the material .

The process is advantageously conducted under steady state conditions which means that in the beginning of the process the type of ions which are produced in the anodic reaction are already pre-added to the electrolyte . It is preferred that under steady state conditions the number of ions which are produced in the anodic reaction and the number of ions which are deposited in the cathodic reaction is equal , which leads to a constant steady state concentration of these ions in the electrolyte . "Constant" refers here to the average concentration in the electrolyte as , depending on the parameters of the process , ion gradients may occur in the electrolyte .

Accordingly, for the above process , it is preferred that the deposited metal is of the same type as the metal which is dissolved in the anodic etching reaction . However, it is not necessary for the deposited ion to originate from the anodic reaction but it may be an ion which has been introduced into the system, for example prior to the start of the deposition However, generally and in particular for a long-term continuous process it is preferable that at least a part of the metal ions which are deposited as metal in the cathodic reaction on the second foil originates from the etched first f oil . Furthermore , the above proposed concept has the additional advantage that the concentration of ions of the etched foil can be kept low or at least constant in the electrolyte . For several etching techniques , in particular for the etching of aluminum foils , the concentration of metal ions must be small , for example smaller than 9 g of aluminum ions per liter . With the above concept it is possible to deplete the solution of the ions which are constantly produced in the anodic etching reaction . This may allow for longer usage of the same electrolyte . Thereby waste of electrolyte may be reduced .

In particular for aluminum foils it is well-established that high surface area materials and nanostructured materials may be produced from aluminum plates or foils via anodic etching .

For such processes typically high purity materials have to be used which have comparatively high material costs . Deposition of aluminum from the solution according to the present invention has the advantage that high purity aluminum materials are created in the cathodic reaction . The electrolytic deposition ( cathodic reaction) even may allow for puri fication of the material used . Accordingly a highly valuable , highly pure aluminum material may be formed .

Preferably the purity of the aluminum foils which are used for etching is in the range of maximum 100 to 150 mg of hetero materials or contaminants per kilogram of aluminum . Even lower concentrations may be preferable . I f impurities in the aluminum foil are too high the electrochemical etching may be hindered, leading for example to highly irregular growth of etching pits . According to a preferred aspect the second foil comprises or consists of the same type of metal as the first foil . This is particularly preferred in the case that both the first foil and the second foil comprise or consist of aluminum .

This has the advantage that no mixed materials are formed and that the metal is deposited on a foil or a platelet of the same metal . Thus the recovering process is more ef ficient as a material consisting of one substance may be formed .

According to a further preferred aspect the process may be carried out in a static process . In the static process both the cathode and the anode are fully immersed in the electrolyte and one and the same area of the anode is subj ect to anodic etching, while one and the same area of the cathode is subj ect to cathodic deposition until the process is finished . A static process may be particularly advantageous for anodi zing platelets or thicker foils with a si ze , which allows for full immersion into an electrolyte bath .

Alternatively larger foils , which have an area that allows for use for example in coiled electrolytic capacitor, may be brought into contact with the electrolyte in a roll-to-roll process step . This means that at least one of the foils is passing through the electrolyte in a roll-to-roll process . In particular it is preferable that the first foil which is structured or etched in the anodic reaction passes through the electrolyte in a roll-to-roll process . I f the cathode is a platelet , which is fully immersed into the electrolyte continuous static deposition takes place at the second foil . More preferably both foils are contacting the electrolyte in a roll-to-roll approach . This means that both foils are dragged through the electrolyte in a roll-to-roll process .

A roll-to-roll process may be understood such that from a first roll or coil a foil is rolled of continuously, while it is continuously rolled onto a second role or coil . A portion of the foil between the first roll and the second roll is suspended between the roles . According to the present invention the foil may pass through the electrolyte bath, wherein a certain fraction of the foil which is suspended between the rolls is in contact with the electrolyte . Thereby the foil is dragged through the electrolyte .

It is another preferred aspect that the first foil is microstructured and/or nanostructured by the electrochemical etching . This means that microstructures or nanostructures may be formed on the first foil by the anodic etching reaction . Nanostructures and microstructures may coexist next to each other . Microstructures may here and in the following be defined as structures which are ranging in the micrometer si ze , which means from 1 pm to below 1000 pm, and preferably between 1 pm and 500 pm . Nanostructures may here and in the following be defined as structures which are ranging in the nanometer si ze , which means structures smaller than 1 pm and larger than 1 nm .

According to a further preferred aspect , the anodic reaction is part of a process of creating a foil to be used in an electrolytic capacitor . In other words , it is preferable that the anodic etching reaction is part of a process of processing a foil , such as an aluminum foil , to be structured for use in an electrolytic capacitor . In the process of producing electrolytic capacitors a substantial amount of the mass of the foil is etched and dissolved into the solution . Accordingly, the above-disclosed process may be most preferably applied to recover some of the material .

Furthermore , according to a preferred aspect the electrolyte is capable of dissolving aluminum salts and enables electrochemical deposition of aluminum from the electrolyte .

Accordingly, for the case of the metal being aluminum, the electrolyte must be able to have aluminum ions dissolved therein and should also provide the capability of deposition of aluminum via the above described process .

According to another aspect , it is preferred that the electrolyte is a non-aqueous electrolyte .

The inventors of the present invention have found out that the above process is preferably conducted with non-aqueous electrolytes . The inventors reali zed that the conventionally used aqueous electrolytes often may not be suitable for the above process , as in aqueous electrolytes instead of metal deposition, water electrolysis takes place in the cathodic reaction .

According to another preferred aspect of the invention, the electrolyte does not have a potential window smaller or equal to that of an aqueous electrolyte . A larger potential window than aqueous electrolytes promotes the deposition of metal and reduces the likeliness of dissociation of the electrolyte . According to a further aspect the electrolyte comprises or is made of ionic liquids and/or deep eutectic solutions . Of these in particular ionic liquids are preferred . However, both ionic liquids and deep eutectic solutions have been found by the inventors to be suitable for dissolving metal ions and for metal deposition . In particular, ionic liquids as well as deep eutectic solutions are especially suited for dissolving aluminum ions and depositing aluminum ions in a cathodic reaction .

In this case it is particularly preferred that the electrolyte consists of ionic liquids in the sense that , except for dissolved substances such as the metal ions , the electrolyte is made of the ionic liquid .

Ionic liquids in the meaning of the present invention are defined as ionic materials that are liquid at temperatures of below 100 ° C . Most preferably ionic liquids comprise organic ions which allow for the ionic material to have a melting point below 100 ° C .

Ionic liquids are very advantageous materials due to their low vapor pressure which allows for an electrochemical process to be conducted without severe material loss due to evaporation even at elevated temperatures . Examples of ionic liquids may comprise imidazolium or pyrrolidinium based ionic liquids such as l-ethyl-3-methylimidazolium tetrachloro aluminate .

According to a further aspect the ion which is formed in the anodic reaction comprises aluminum ions and chloride ions .

For example it may be an aluminum chloride complex . Most preferably the aluminum chloride may be A1₂C17~ . It has been found out by the inventors that these ions are readily dissolvable in several ionic liquids and are technically highly advantageous for aluminum to be deposited in a cathodic reaction .

Furthermore , it is preferred that the electrolyte in this case is l-ethyl-3-methylimidazolium tetrachloro aluminate . In this electrolyte the A1₂C17~ complex may be formed during the anodic etching reaction . The cathodic reaction allows for deposition of aluminum from this ion .

The following reaction 1 can be the cathodic metal deposition reaction :

Reaktion 1 : 4 A1₂C17~ + 3e~ Al + 7 A1C14-

The formation of A1₂C17~ is favored by high mole fractions of aluminum tetrachloride (AlCla ) , which are preferably present in l-ethyl-3-methylimidazolium tetrachloride aluminate with a mole fraction of 0 . 67 to 0 . 75 . In this concentration window the stability of the previously mentioned electrolyte is most preferred to allow for both the cathodic and anodic reaction .

According to a further preferred aspect the structures resulting from the cathodic deposition have a structure or pattern on the micro or nano level . This may be achieved such that the electrochemical parameters of the process and of the cathodic reaction in particular are set such that the deposited metal forms micro- and/or nanostructures on the second foil . By these means various types of nanostructures for several possible uses may be achieved . In particular surface enhancement may be achieved . Thus a high surface area foil can be formed by the cathodic reaction and by the anodic reaction simultaneously .

Furthermore , it is even more preferred that the second foil which is used in the cathodic reaction is already micro- or nanostructured and/or surface enhanced prior to the metal deposition in the cathodic reaction . By forming, for example , new or additional micro- or nanostructures in the cathodic reaction hierarchical structures may be formed . Also , this approach may allow for additional surface enhancement .

Enhancing the surface area by anodic etching is limited to a certain maximum due to statistical distribution of etched tubes and the fact that the tubes must remain separated by a wall . However, a previously anodically etched foil may be used as the second foil for cathodic deposition . By applying additional micro- or nanostructures to the previously etched foil during cathodic reaction, the surface may be even more enhanced . This means that the process can be applied to enhance the surface of an etched foil , not only to recover material .

Accordingly the process can also be applied in a cyclic form, such that in a first step a first foil is etched against any counter electrode and micro- or nanostructured by anodic etching . This foil may then be used for the cathodic reaction as the second foil , while a further first foil is nanostructured in the anodic reaction . By using an anodically etched foil as the second foil , a fully continuous process can be established . Furthermore , it is preferable that the nano- or microstructures formed by the cathodic reaction are grainlike or wire-like .

For the grain-like structure it is preferred that the grains are deposited on surfaces with already existing nanostructures such as tubes which may be formed by anodic etching .

The wire-like structure already has a very high surface area so that it may be used on a plane foil to enhance its surface area . However, it can also be applied to already previously nanostructured foil .

Please note that the shape of the deposited material may depend on the conditions of the electrochemical reaction, in particular the voltage , the deposition time and the concentration of the ions in the electrolyte , the deposition temperature and so forth .

According to another aspect of the present invention a capacitor foil is described which is formed by the anodic reaction or cathodic reaction as previously described . In this context it is most preferred that such foils can be incorporated into a capacitor and may be described as capacitor foils . Furthermore , a capacitor using or comprising these foils is described .

In the following the invention is described in more detail by means of examples of embodiments and with reference to figures . The figures include both embodiments and process- related information . It is noted that the components are not shown to scale in schematic drawings . In these , components may be shown distorted in their si zes , lengths or length ratios . Such ratios may not be taken from the schematic drawings .

Figure 1 shows a schematic representation of an electrochemical setup .

Figure 2 shows a section of a cross-section image of an electrolytic capacitor .

Figure 3 shows a cross-section image of a high voltage capacitor foil after first step of the etching process .

Figure 4 shows a cross-section image of a high voltage capacitor foil after a widening process .

Figure 5 shows a schematic representation of a forming process .

Figure 6 shows a top view of an etched foil with a stochastic pore distribution .

Figure 7 shows a zoomed in top view on the image of Figure 6 .

Figure 8 shows a pole figure of a high cubic texture .

Figure 9 shows an electrode back scatter di f fraction pattern in false color presenting small angle variations from an ideal texture plane . Figure 10 shows a top view on a schematic representation of cathodic electro-deposited aluminum particles on a porous etched foil .

Figure 11 shows a side view cross-section of a schematic representation of cathodically electro-deposited aluminum particles on a porous etched foil .

Figure 12 shows a pure metal aluminum layer which has been obtained from deposition in ionic liquid ( Source : An electrochemical quartz crystal microbalance study on electrodeposition of aluminum and aluminum-manganese alloys by Adriana I spas , Elisabeth Wol f f , and Andreas Bund in the Journal of The Electrochemical Society, 164 ( 8 ) H5263-H5270 ( 2017 ) ) .

Figure 13 shows a wire-like structure of an aluminum- containing compound deposited in a cathodic reaction in ionic liquid ( Source : Potential Oscillation Associated Galvanostatic Deposition of Periodic Al Wires from a Chloroaluminate Ionic Liquid by Chung-Jui Su and I-Wen Sun in ECS Electrochemistry Letters , 4 ( 7 ) D21-D23 ( 2015 ) ) .

Figure 1 shows schematic representation of an electrochemical setup 1 . In the electrochemical setup 1 an anode 2 and a cathode 3 are connected to a voltage supply 6 . Furthermore , both the anode 2 and the cathode 3 are immersed in an electrolyte 4 . The electrochemical reaction ( coupled etching and deposition process ) is conducted in a reaction vessel 5 . When a voltage is applied to the anode 2 which comprises a metal M the anode is etched and the metal M dissolves , releasing metal ions M+ into the electrolyte 4 . Please note that here M+ stands for any type of metal ions in which the oxidation state has been increased . In particular in the anode 2 the metal is present in oxidation state 0 and becomes oxidi zed to become M+ . However the metal ion in the electrolyte may be in a complex or similar structure which also may have a neutral or negative net-charge , for example due to anions surrounding the metal ion .

In the overall process the metal ion M+ is di f fusing towards the cathode 3 . At the cathode 3 the metal ion M+ becomes reduced and is re-deposited as metal M . Preferably both the cathode and the anode consist of the metal M . Furthermore , it is preferred that the electrolyte already contains an amount of metal ions M+ at the start of the coupled etching and deposition process .

Furthermore the process according to the setup is conducted such that a steady state is reached in which the amount of metal ions formed at the anode is equal to the amount of metal ions deposited at the cathode for a certain time , which means that the formation rate of metal ions should be equal to the deposition rate of the metal ions .

Most preferably the metal M is aluminum (Al ) . Furthermore , it is preferred that the electrolyte is an ionic liquid, in particular it is preferred that the electrolyte is l-ethyl-3- methylimidazolium tetrachloro aluminate .

In the simpli fied scheme of Figure 1 the anode 2 and the cathode 3 are platelets or foils which are statically fully immersed in the electrolyte .

Alternatively the cathode or the anode , or both of them, may represent a fraction of a band-like foil which is dragged through the electrolyte in a roll-to-roll process . This means that in this case only a fraction of the band-like foil is in contact with the electrolyte .

Figure 2 shows a cross-section image of an electrolytic capacitor 7 comprising an anode foil 9 which comprises an oxide layer and a cathode foil 8 with fine pores . In between a separator paper with electrolyte 10 is arranged .

Electrolytic capacitors are passive devices that can be used in electric circuits for charge storage . Electrolytic capacitors have a wide range of applications , in particular in applications in which a fast charge and discharge is required . The general basic construction that can be seen, for example in Figure 2 is composed of two conductive electrodes 9 and 8 and a dielectric material in between ( separator and electrolyte 10 ) . In the case of an aluminum electrolytic capacitor both the anode 9 and the cathode 8 are made of aluminum . The anode 9 is covered with aluminum oxide and the oxide adds a dielectric function to the anode 9 . Both the anode 9 and the cathode 8 present a high speci fic surface area in order to store as much charge as possible according to the capacitor equation : C = E x A/D . Here C is the capacitance ; E is the electric constant ; A is the surface area of the capacitor ; D is the thickness of the dielectric material .

Electrolytic capacitors having aluminum foils as electrodes can have high withstand voltages in the order of 1000 V, which is achieved by an electrochemical forming process after an etching such as in an anodic reaction according to the invention . Figure 3 and Figure 4 show cross-section images of a high voltage capacitor foil after a first step of etching and after a widening process , respectively . In Figure 5 a forming process is represented schematically .

Etched anode foils are fabricated in an electrochemical dissolution process using high purity aluminum foil , for example with purity grades of 99 . 99% . The foil may have a thickness of about 110 to 120 pm .

The etching process can be composed of the following four steps : first pre-treatment , which is for example a surface activation process , second pre-etching, which forms etch tunnels , third tunnel widening and fourth surface cleaning and drying .

In a roll-to-roll process in a continuously running machine the aluminum foil may enter into the electrochemical bath under anodic polari zation . In the case of the present invention non-aqueous electrolytes are used, such as ionic liquids or in deep eutectic solutions .

In the pre-etching step during anodic dissolution, vertical tunnels on both sides of the foil are formed, which may have a pore diameter in the range of 0 . 5 to 0 . 7 pm . This si ze range characteri zes the pores as nanostructures . A tunnel density in the range of 20 million/cm² may be reached with a stochastic tunnel distribution .

Depending on the etching conditions , other pore diameters may be reached . During the anodic etching, aluminum is dissolved into the electrolyte . In the tunnel widening step the tunnels are widened, which causes further dissolution of aluminum into the electrolyte . The tunnel widening step is a controlled surface dissolution with special precaution in avoiding thickness loss of the foil . The loss of too great a thickness would mean a complete dissolution of the initial part of the already created tunnels which would result in the loss of speci fic surface area and of capacitance in a capacitor application . A tunnel diameter of 1 . 2 pm can be obtained with a loss of foil thickness in the range of total 5 to 10 pm . The tunnel diameter of 1 . 2 pm can be characteri zed as falling into the micrometer range . Any ulterior diameter enlargement may cause unsustainable performance loss . Regarding the tunnel diameter, another performance limitation is the irregular distribution and irregular diameter of the primary tunnels formed during the pre-etching step .

Accordingly the maximum surface area which may be reached according to the state of the art using purely anodic etching is limited . As is disclosed below, the inventive process has the advantage that the surface may be even further enhanced in addition to the recovery of dissolved material .

During the formation process , also an oxide layer is formed on the anodic aluminum foil surface . As this oxide layer is insulating and continuously increases in thickness during continuous anodic etching, the forming voltage may have to be increased with a ratio of 1 nm of additional oxide thickness per volt to form a certain thickness . Furthermore , the tunnel diameter must be large enough to contain the oxide layer and possibly maintain the active surface area . The present etching technology is optimi zed to create a tunnel diameter in the micrometer range , for example such as 1 . 0 to 1 . 2 pm . During the following steps the surface of the etched aluminum foil is cleaned from the etching reagents ( electrolyte or other regents ) by means of chemical treatments and washing steps . The final step of the etching is an inline heat treatment which serves to dry and passivate the surface of the etched foil . Subsequently a formation process composed of four steps is applied . A pre-treatment is performed in which hydrogen is formed from a reaction with hot water . Second, a bulk oxide layer is created on the surface in a forming step . Third, during a depolari zation step wetting of cracks in the voids formed during the forming step is performed . The final forming is performed in a fourth step in which the oxide layer is repaired by means of repolari zation .

In the first step of the formation process or forming process in the pre-treatment step the etched foil is dipped in a hot water tank . This leads to the reaction of aluminum with hot water and creates a complex aluminum hydroxide structure . The structure of the hydroxide is of boehmite type . A boehmite type layer is created .

In the second step an anodic polari zation of the foil in neutral electrolytes is performed and converts the boehmite layer into gamma alumina and creates an additional oxide layer directly by the oxidi zation of metallic aluminum . The conversion of metallic aluminum to aluminum oxide is associated with a change in material density ( the density of aluminum is 2 . 7 g/cm³ whereas the density of aluminum oxide is 3 . 8 g/cm³ ) . Due to this change in density, formation of cracks and voids may take place inside the oxide layer . In a follow-up chemical treatment , these defects are first wetted thoroughly with an electrolyte ( third step / depolari zation step ) , and then repaired in the final forming step by means of anodic polari zation .

In Figures 6 and 7 scanning electron microscopy images of a foil with a statistical pore distribution which can be achieved with the inventive process , is shown . The magni fication of the scanning electron microscopy image of Figure 6 is one thousand fold . The magni fication of the scanning electron microscopic image of Figure 7 is five thousand fold .

For the process high purity aluminum foil is required which is prepared containing selected hetero dopants in a concentration range of 100 to 150 mg/ kg with the purpose of increasing the etch capabilities of the metal . Here the term "etch capabilities" summari zes all performance parameters of the raw foil material which are required to obtain a maximum speci fic surface in connection with a suitable etching process . In particular one desired parameter is the high cubic texture of the foil which is preferred to be up to 95% and more preferably up to 98 % or more preferably even higher than 98 % . A high cubic texture indicates that the 100 direction is the preferred orientation of the lattice of the foil . A high cubic texture may be reached by a casting process in combination with rolling technologies and a final annealing step . A high cubic texture with a high degree of orientation is required as the etch pits initiate at the 100 planes of the cubic crystal . With a high cubic texture , a more regular pit distribution can be achieved . However, for practical reasons , a mainly statistical distribution as shown in Figures 6 or 7 is reached . In Figure 8 pole figures of the cubic texture are shown . In Figure 9 an electron back scattered di f fraction pattern with a false color representation showing the small angle variations from an ideal texture of a plane is shown . Please note that in Figure 8 the arrow and the sign RD indicate the rolling direction of the measurement .

In Figures 10 and 11 schematic representations of electrodeposited aluminum particles on porous etched foils is shown . It is depicted that by a cathodic deposition reaction applied to a previously etched porous aluminum foil additionally nanoparticles 11 may be deposited on the foil having pores 12 .

This deposition allows for the surface area of a porous foil to be increased, in addition to the advantages of recovering material which otherwise would be lost in case of a usual non-coupled anodic reaction .

In Figure 12 a pure aluminum layer is shown, which has been obtained by cathodic deposition from a 2 : 1 AI2CI3 to 1-ethyl- 3-methylimidazolium solution at room temperature at a voltage of - 0 . 2 V ( Source : An electrochemical quartz crystal microbalance study on electrodeposition of aluminum and aluminum-manganese alloys by Adriana I spas , Elisabeth Wol f f , and Andreas Bund in the Journal of The Electrochemical Society, 164 ( 8 ) H5263-H5270 ( 2017 ) ) .

Similar grain-like structures as can be seen in Figure 12 may be obtained via the deposition in a cathodic reaction which is coupled to an anodic reaction according to the present invention . In Figure 13 wire-like structures are shown, which have been generated at 0.25 mA/ cm² in an electrolyte comprising a ratio of 58:42 mol% of AICI3 to 3-methylamine hydrochloride (Source: Potential Oscillation Associated Galvanostatic Deposition of Periodic Al Wires from a Chloroaluminate Ionic Liquid by Chung-Jui Su and I-Wen Sun in ECS Electrochemistry Letters, 4 (7) D21-D23 (2015) ) .

Also, under the right process parameters, similar wire-like structures may be reached for a coupled cathodic reaction according to the invention.

Accordingly, Figures 12 and 13 show that different morphological forms with different surface areas may be formed via cathodic deposition.

This system might even be extended to produce mixed composites if additives, such as MnC12 salt would be added to the electrolyte. With such mixtures a hybrid material such as AIMn could be formed via deposition.

When the above composites are oxidized, mix oxide dielectrics with improved capacitor performances might also be achieved.

Reference signs :

1 electrochemical setup

2 anode 3 cathode

4 electrolyte

5 reaction vessel

6 voltage supply

7 electrolytic capacitor 8 cathode of the electrolytic capacitor

9 anode of the electrolytic capacitor

10 separator and electrolyte

11 nanoparticle

12 pore

Claims

23 Claims (We claim)

1 . Coupled etching and deposition process in which an anodic reaction is coupled to a cathodic reaction such that in the anodic reaction a first foil containing a metal is electrochemically etched in an electrolyte whereby ions of the metal are dissolved into the electrolyte , and whereby in the cathodic reaction ions of the metal from the electrolyte are deposited on a second foil .

2 . Process according to claim 1 , wherein the metal is aluminum .

3 . Process according to claim 1 or 2 , wherein the second foil comprises the same type of metal as the first foil .

4 . Process according to one of claims 1 to 3 , wherein one or both of the foils are brought into contact with the electrolyte in a static process or in a roll-to-roll process step .

5 . Process according to one of claims 1 to 4 , wherein the first foil is micro- and/or nanostructured by the electrochemical etching .

6 . Process according to one of claims 1 to 5 , wherein the anodic reaction is part of a process of forming a foil to be used in electrolytic capacitor .

7 . Process according to one of claims 1 to 6 , wherein the electrolyte is capable of solving aluminum salts and enables electrochemical deposition of aluminum .

8 . Process according to claim 7 , wherein the electrolyte is a none-aqueous electrolyte .

9 . Process according to claim 7 or 8 , wherein the electrolyte has a larger potential window than aqueous electrolytes .

10 . Process according to one of claims 1 to 7 , wherein the electrolyte comprises or is made of ionic liquids and/or deep eutectic solutions which enable aluminum deposition .

11 . Process according to claim 10 , wherein the ions formed in the anodic reaction comprise aluminum ions and chloride ions .

12 . Process according to one of claims 10 or 11 , wherein the ionic liquid comprises l-ethyl-3-methylimidazolium tetrachloro aluminate .

13 . Process according to one of claims 1 to 12 , wherein electrochemical parameters are set such that by the cathodic reaction the deposited metal forms micro- and/or nanostructures on the second foil .

14 . Process according to claim 13 , wherein the metal foil is already micro- and/or nanostructured and/or surface enhanced prior to the deposition in the cathodic reaction .

15 . Process according to claim 13 or 14 , wherein the structures formed by the second hal f-cell reaction have grain-like or wire-like structure .

16 . Foil to be used in electrolytic capacitor which is formed by the anodic or cathodic reaction according to one of claims 1 to 15 .