WO2012076963A1

WO2012076963A1 - Method for producing an electrode with nanometric structure and electrode with nanometric structure

Info

Publication number: WO2012076963A1
Application number: PCT/IB2011/002948
Authority: WO
Inventors: Carmelo Sunseri; Salvatore Piazza; Rosalinda Inguanta; Germano Ferrara; Maria Chiara Mistretta; Francesco Gioacchino Vergottini
Original assignee: Cr Mobility Solution System
Priority date: 2010-12-10
Filing date: 2011-12-07
Publication date: 2012-06-14
Also published as: ITVI20100333A1

Abstract

A method for manufacturing a nano-structured electrode, comprising the steps of providing a nano-porous matrix (6) having at least one active surface (7) and a plurality of substantially cylindrical pores (8) with diameter of nanometric size, providing a first electrolytic cell (9) containing an electro-deposition bath comprising a first electrolytic solution containing metallic salts, coupling of a first substrate (5) in a first electrically conductive material to said active surface (7) of said matrix (6), immersing said active surface (7) coupled to said first substrate (5) into said first electrolytic cell (9), growing nanowires (3) in a metal alloy of said salts inside said cylindrical pores (8) by feeding with a potentiostatic or galvanostatic current to promote the growing of the nanowires directly on said first substrate (5) and define a nano-structured charge collector, a step of removing said nano-porous matrix (6) from said collector being also provided to realize the electrode.

Description

"METHOD FOR PRODUCING AN ELECTRODE WITH NANOMETRIC STRUCTURE AND ELECTRODE WITH NANOMETRIC STRUCTURE"

DESCRIPTION

Technical Field

The present invention generally concerns the technical field of the electrical devices and particularly relates to a method for manufacturing a nano-structured electrode having high power density designed to be used into electrical devices, such as power accumulators, sensors and in catalysis.

The invention also relates to a nano-structured electrode adapted to be manufactured with such a method.

Background art

As known, using nano-structured metallic materials for manufacturing electrodes is a particularly common technique as these materials allow to obtain electrodes with higher performance than the traditional electrodes, in particular in terms of power density provided by the powered device.

Further, the nano-structured electrodes provide the reduction of the charging time and the increasing of pickup current of the battery due to the reduction of the distances of diffusion of the reactants from and toward the active materials during the several steps of the life-cycle of a such an electrical device. These properties are particularly advantageous if the electrodes are used as anodes of accumulators.

In this case, using nano-structured materials in a metallic alloy is known for manufacturing anodes of battery with lithium ions, commonly defined Li-ion battery. This peculiar type of accumulators has the advantage of granting power density and specific power higher than the other accumulators.

Thus, the Li-Ion batteries allow to transport more energy power than any other secondary battery with same size and mass, or to supply the same power having lower size and mass.

Moreover, they could be advantageously charged by chemicals reactions that restore the energy level of the electro-active materials used for the cathode and for the anode. The more common Li-Ion batteries are constituted by a pair of electrodes operating as anode and cathode, separated by a polymeric septum that avoids their short-circuit and that operates as support for the electrolytes. The Li-ion accumulators normally available on the market are characterized by a cathode of lithium cobalt oxide (L1C0O2) or other mixed oxides such as LiNio.33Coo.33Mno.33O2.

These materials are characterized by a fairly low theoretical capacity, generally close to 150 Ah/kg, but with an average intercalation voltage quite high and variable depending on the material, with values comprised between 3,6 and i 4,2 V relative to lithium.

The anode is instead made of a carbon-based material, e.g. graphite, with low theoretical capacity, of 372 Ah/kg, and average intercalation voltage of about 0,1-0,2 V relative to the lithium reference.

By this way it is possible to obtain a voltage difference between the electrodes of at least 3,5 V.

In the spontaneous process of charge the electric power is supplied from the outside through the electric contacts, causing the oxidation of the lithium into Li⁺ which migrates through the liquid electrolyte and reduce to the anode thanks to the electron supplied by the outer circuit, restoring the starting charge condition.

These batteries are characterized by a middle-low capacity of storing energy, even if they have a very high stability, allowing the execution of a high number of cycles of charge and discharge, due to the presence of the graphite anode, having high mechanical and chemical stability.

As a consequence, these known accumulators are suitable to feed electronic devices with low absorption, e.g. small household appliance, but they are not much suitable to feed more complex devices such as electric or hybrid motors requiring a higher energy and specific power amounts.

To improve the capacity and the electromotive force and producing accumulators able to provide higher power density, materials with high stability and low values of intercalation with Ll⁺ have been used, able to reacts with great amount of Li⁺. As matter of fact, the intercalation voltage of the tin is higher than the graphite and this improve the safety of the battery.

Among these materials, tin has resulted particularly suitable, due to its high theoretical capacity, close to 994Ah/Kg, other than to the reduced cost and to the substantial non- toxicity.

The use of tin as anode in Li-Ion accumulators allows to increase the safety of the same device. An anode made of graphite reacts with lithium at an average tension of 0.1-0.2 V, as already said. These values are close to the conditions for the formation of metallic lithium that, growing in a dendritic way may constitute dangerous short circuits. By contrast, using tin provides an average lithium alligation voltage of about 0.5-0.6 V vs. lithium.

However, the main drawback of using tin in the Li-Ion batteries is represented by the presence of plastic deformations that occur in the material of electrode during the charging and discharging processes due to the reactions between tin and lithium which during time may bring to the pulverization of the material and to the loss of the electric contact with the current collector.

The use of nano-structured materials allows to overcome at least part of these drawbacks, allowing to reach, between these accumulators, several advantages in term of performance and of available power density.

As matter of fact, the nanowires electrodes have a wide surface exposed to the reaction environment, allowing the optimal use of the electro-active material, that, in the charging processes, should oppose the lower possible resistance to the diffusion of the Li⁺ ion in the anodic material.

In this view, the use of nanowires is particularly advantageous because they are characterized by a high surface/volume ratio.

Moreover, the nano-structured wires have higher mechanical strength, allowing the use of more fragile materials, but making a structure with higher mechanical strength than the same not nano-structured material. By way of an example the not nano-structured tin is not more active after few charging/discharging cycles, while the nano-structured tin may execute up to 280 cycles.

A further advantage of the accumulators with a nanowires anode with respect to the common Li-Ion batteries is represented by a better absorption of the above cited plastic deformations which occur in the anodic material.

Generally, the process of manufacturing nanowires electrodes comprises a growing step of the nanowires in a metallic alloy inside an electrolytic cell and their following application to a collector, typically made of copper, for realizing the electrode.

A specific process of growing the nanowires is disclosed in the Italian patent application RM2008A000341 , from the same inventors of the present application, wherein a process of manufacturing nanowires in a Sn-Co alloy is disclosed.

A first drawback of the electrodes manufactured in this way is represented by the reduced stability of the coupling between the wires and the current collector.

As matter of fact , generally the copper is used as a film-shaped copper on which a semi-fluid paste is distributed which is constituted by the electro-active material in a powder shape, by the binding materials and other substances adapted to improve the electric conductibility.

However, using the binder, needed to allow the diffusion of the Li⁺ ion, other than the adhesion of the electro-active material to the collector, produces the increasing of the inner resistances and need the use of materials improving conductibility, such as carbon powder.

It is apparent that similar additions produce the increasing of the weight and costs of the electrode and a reduction of the efficiency thereof.

Moreover, the growing process of the nanowires disclosed in the above cited patent application, even though improved relative to the other previous processes, resulted limited in the eventual applications either because it only uses cobalt together with tin, or for the type of the selected materials for the nano-porous membrane and of the chelating materials used in the electrodeposition process of tin and cobalt.

US6465132 discloses a method for manufacturing nano-structured electrodes which provides the manufacturing of a support in a binary alloy on which determining the growing of the nano-structured wires. Such a method wants mainly produce a support or template from which catalyzing the growing of carbon-made nano-tubes.

Particularly, the support is made by almost complex and expensive thermal treatments which allow to realize carbon nanowires, always in hard conditions, by means of a physical-chemical process named CVD (Chemical Vapor Deposition).

The so realized material has theoretical specific capacity of 372 mAh/g, much more lower than the one which could be obtained with tin alloys with which it's possible to reach up to about 1000 mAh/g.

Moreover, due to the density differences between the two materials, with tin, for the same mass, the occupied volume is about 4 times lower than using carbon, and, therefore, for the same occupied volumes, capacity about 4 times greater.

Manufacturing of nanowires is only provided in the step of selective etching of the catalytic portion of the alloy and thus these wires could not be higher than few millimeters.

Finally, not the all systems disclosed in this document and used for producing the alloy, such as the Fe-Cr systems, can be used into batteries because they could corrode themselves.

From US20090316335 a method is known for electrolytically manufacturing nano- structured conductive elements which method provides the direct contact between the active material and the current collector by means of the pressure exerted during the step of deposition for electrochemical reaction.

However, the nano-structured wires and the collector have the same chemical nature while the active material is placed on the wires in a second step.

Alternatively, the current collector and the wires may be constituted by active material, with limitation in the application of the electrode into Li-Ion battery due to the properties of the current collector and to the low performance of the film of material.

Lastly it's necessary to consider that when the nanowires of active material are into contact with a current collector of the same nature, they would react therewith, which collector, being not nano-structured, would mechanically collapse after few cycles.

Moreover, such a method provides the manufacturing of nanowires on a copper current collector with a thickness of 500 micron, greater than the about 20 micron normally used for the common Li-ion batteries.

An excessive thickness of the current collector not only entails an increasing of the expense to be sustained to realize the battery and a reduction of its whole efficiency, due to the increasing of the mass of the materials which have no interaction with the lithium reaction, but it also would not allow the formation of a winding of the active materials, so avoiding the production of accumulators with more compact and powerful shapes, e.g. cylindrical or prismatic.

Disclosure of the invention

The object of the present invention is to overcome the above drawbacks, providing a method for manufacturing a nano-structured electrode having high efficiency and relative cost effectiveness.

A particular object is to provide a method for manufacturing a nano-structured electrode having high power density. A particular object is to provide a method for manufacturing an electrode having an electric collector firmly connected to the nanowires.

Yet another object is to provide a method for manufacturing an electrode having nanowires with variable composition suitable for the performances to be obtained for each proper use of the electrode, increasing the field of application of the electrodes obtainable with such a method.

Yet another object is to provide a method for manufacturing an electrode having nanowires with variable shape and distribution.

A further object is to provide a nanowires electrode having highly stable contact between the wires and the collector, increasing the electric conductibility.

Yet another object is to provide an electrode with high power density which allows to manufacture power accumulators having relatively reduced encumbrance and weight relative to the accumulators with same electric performances or higher performances with the same size.

These and other objects, as more clearly explained hereinafter, are fulfilled by a method for manufacturing a nano-structured electrode with high power density as claimed in claim 1.

Thanks to this combination of features it's possible to obtain an electrode characterized by a mechanically very stable coupling between the collector and the wires.

Thus, it could be possible to take advantage of the electric output of the nano-structured materials together with a high electric conductibility, as it will be not necessary using binding elements between the collector and the metallic wires.

As a consequence, the electrode will be also more compact and lightweight.

Opportunely, the method may comprise a deposition step of the first substrate of the electrochemical, potentiostatic or galvanostatic type, or carried out by lamination adhesion of a copper film on the support structure.

In each case, the growing process of the alloy nanowires will be carried out electrolytically and thus it will only occur in presence of the electric contact between the material of the first substrate, e.g. copper, and the electrolyte.

As a consequence, the nanowire will be firmly anchored to the first substrate, granting better electric conductibility and avoiding the use of binding materials or materials that improve the electric conductibility. Thus, when the electrode is used as anode in a Li-Ion battery, an improvement in the diffusive processes at the solid state of lithium ion will also occur.

In a further aspect a high power density electrode is provided which is obtainable with the above method and according claim 10.

Advantageous embodiments of the invention are defined by the dependent claims.

Brief description of the drawings

Further features and advantages of the invention will become more apparent in view of the detailed description of preferred but not exclusive embodiments of the method of the invention and of an electrode obtainable with such a method, described by way of a non limiting example with the help of the annexed drawing tables wherein:

the FIG. 1 is an elevated view of an electrode of the invention;

the FIG. 2 is an elevated view of an assembly contact-matrix 10 designed to be used for manufacturing the electrode of the invention;

the FIGG. 3 and 4 are imagines at scanning electron microscope (SEM) of the nanowires of an electrode of the invention, respectively in a SnCu alloy and in a SnCo alloy, obtained according two different growing methods;

the FIGG. 5 and 6 are graphics relative to a diffractometer analysis for a CuSn alloy for the electrodes of Figg. 3 and 4, respectively;

the FIG. 7 is a schematic view of some of the steps of a method of the invention for manufacturing an electrode.

Best mode of carrying out the invention

Referring to Fig. 1 an eventual embodiment of a high power density electrode of the invention is schematically shown, generally designed by number 1.

The electrode 1 may be used into electric devices, not shown, having a feeding electric circuit and at least one electrolyte for transporting the electric charge.

Particularly, the electrode 1 may be used as cathode or, preferably, as anode in any type of accumulators.

A preferred application may be as anode in Li-Ion batteries, Lithium polymer batteries or Li-air batteries for feeding electric or electronic devices, either for low absorption household or personal appliances or, adequately sized, for feeding more complex appliances such as electric or hybrid motors.

In an exemplificative and not limiting way, the electrode 1 may be also used inside sensors for detecting variation in the electric charge or as catalysis electrode.

Basically, the electrode 1 will comprise a plurality of nanowires, generally designed 3, in a preferably amorphous metallic alloy, and an electrically conductive first substrate 5 electrically into contact with the nanowires 3 to define a non-structured charge collector. Particularly, the first substrate 5 will be designed to be electrically connected to the electric circuit of the device wherein the electrode 1 will be inserted to define the electric charge collector thereof.

The alloy constituting the nanowires 3 will be preferably made by at least one first and one second component electrically connected to the first substrate 5 to chemically interact with an electrolyte and produce an electric charge.

In a first preferred embodiment a second substrate 2 in a second material with high electric conductivity will be also provided which will be applied to the first substrate 5. Advantageously, the second substrate 2 will be distributed on a surface 4 of the first substrate 5 and, in some circumstances that will become clearer in the following, the first substrate 2 may also be absent.

Moreover, at least part of the nanowires 3 have one end integral to the surface 4 of the second substrate 5 to obtain a stable electric contact therewith, and thus with the collector, to increase the electric conductibility of the electrode 1.

In particular, according a particularly advantageous aspect of the invention, the nanowires 3 may be obtained by direct growing of the metallic alloy on the first substrate 5 and possibly on the second substrate 2 if provided.

The first substrate 5 will be made of a first metallic material with high electric conductibility.

Preferably, the first material will be selected into the group comprising copper and the like.

The second material of the second substrate 2 will be also preferably a metal with electric conductibility at least equal to the material of the first substrate 5 to provide the electric continuity between the nanowires 3 during their growing.

Preferably, the second material will be selected into the group comprising gold, platinum, palladium, copper, tin.

Moreover, the second substrate 2 may be distributed on the first substrate 5, in a substantially discontinuous manner, e.g. by physical or chemical techniques which will be next disclosed in a more detailed way, to allow the contact of the nanowires 3 with the first substrate 5.

The second substrate 2 will have generally limited thickness s-i , e.g. comprised between 10nm and 40nm and preferably between 20nm and 30nm.

Thus the right electric connection between the wires 3 will occur, minimizing the expenses and the total weight of the whole electrode 1.

The first substrate 5 may have thickness S2 greater than the thickness Si of the second substrate 2.

By way of example, the first substrate 5 will be a substantially continuous film with even thickness S2 comprised between 5pm and 20pm and preferably close to 15pm.

The selection of the metallic materials constituting the alloy of wires 3 will be carried out as function of the specific application which the electrode is designed to.

Particularly, a first component of the alloy may be a metallic or metalloid material selected into the group comprising tin, aluminium, silicon, germanium.

A second component of the alloy may be instead selected, without any limitation, among the metals of the fourth period of the periodic table of the chemicals elements.

By way of an example, the wires 3 may be in a binary or ternary metallic alloy of tin and at least one of the above cited metals of the fourth period.

The size of the nanowires 3 depends on the size of the support matrix 6 or template used for their growing, shown in Fig. 2, and more clearly disclosed on the later.

Generally, they will have diameter of few nanometers, e.g. between 10nm and 400nm, and length between 1pm and 70pm. By way of example, in Fig. 4 nanowires 3 having length of about 3pm are shown.

Conversely, their distribution on the first substrate 5 will depend by the peculiar embodiment of the matrix 6 used as mould or template during growing step. The number of wires 3 which could be obtained will be generally comprised between 10¹²/m² and 10¹³/m².

By way of example in Figg. 3 and 4 two particulars of two different electrodes 1 of the invention are shown.

In particular, in Fig. 3 nanowires 3 in CuSn alloy are shown which are obtained by growing in a polycarbonate matrix 6.

In Fig. 4 nanowires 3 in CoSn alloy are shown which are obtained by growing in a matrix 6 in anodic alumina and having a distribution more even than that of Fig. 3, with substantially parallel extension.

In Figg. 5 and 6 graphics are shown relative to a diffractometer analysis for the electrode 1 of Fig. 3 and Fig. 4, respectively, by which it's possible to define the crystallographic structure of the wires 3.

In particular, in Fig. 5 it's possible to identify peaks due to the tin and peaks due to an inter-metallic compound, in this case to a CueSn₅ alloy with known and fixed composition. In Fig. 6 peaks relative to tin are instead identifiable.

In both the graphics peaks due to copper of the current collector 5 are further identifiable. From the graphic of Fig. 6 it can be observed that there's no evidence neither of an inter-metallic SnCo compound, nor of cobalt or other phases containing this metal, allowing to say this material is amorphous.

In Fig. 7 a preferred but not limiting method for manufacturing the above disclosed electrode 1 is schematized.

According to a preferred but not limiting embodiment of the invention, the method will comprise a first step a) of providing a nanoporous support matrix 6 having at least one active surface 7 and a plurality of substantially cylindrical pores 8 with a nanometric diameter.

The nanoporous matrix 6, commonly defined template, may comprise or to be constituted by a membrane in a nanoporous material selected between the ceramic or polymeric materials.

For example, the nanoporous matrix 6 may be constituted by a ceramic material, such as alumina, titanium oxide or the like, or by a polymeric material, e.g. of the organic- based type such as polycarbonate, polyethylene terephtalate (PET) or the like.

The selection of the material will determine the configuration and the distribution of the nanometric cylindrical pores 8.

Such pores 8 will have generally variable length between 7pm and 60pm and transverse dimension or diameter comprised between 15nm and 400nm.

The pores 8 may be substantially parallel, such as in case of a matrix 6 in anodic alumina, or have extension directions incident with each other, such as in case of a polycarbonate matrix 6.

The number of nanometric pores 8 may be comprised between 10¹²/m² and 10¹³/m² with an average porosity comprised between 20% and 40%.

The method comprises a possible following step b) of deposition, in a discontinuous manner, of the second substrate 2 in the second electrically conductive material, preferably metallic, on the active surface 7 of the matrix 6 to define an electric contact. Then, a step c) of providing a first electrolytic cell 9 is provided which cell contains an electrodeposition bath comprising a first electrolytic solution with predetermined concentration of metal salt.

The assembly 10 made by the active surface 7 and the electric contact defined by the second substrate 2 will be successively inserted (step d) in the cell 9 and immerged in the electrodeposition bath.

In a known manner, internally of the first electrolytic cell 9 two electrodes will be present, a first one 11 being the reference electrode while a second 12 will operate as counter-electrode for the execution of the anodic process.

As an example, the first electrode 11 will be a saturated calomel electrode, connected to the electrolytic cell 9 through a salt bridge, while the second electrode 12 may be a wire of graphite or platinum.

The assembly 10 and the two electrodes 11, 12 will be connected to a potentiostat 13 or to a galvanostat, not shown, to allow the circulation of the current with constant potential or constant intensity, respectively.

In such a manner the assembly 10 could be fed in a step e) for promoting the growing of nanowires 3 in a metal alloy, preferably with an amorphous structure, by electrochemical deposition of the metals of the salt present in the solution of the bath inside the cylindrical pores 8.

In a known manner, the assembly 10 may be anchored at its conductive side to a plate 14 in a conductive material, e.g. stainless steel.

Moreover, the selection of the conductive active surface 7 may be delimited by the use of an insulating material, e.g. a paint or a flange suitable for the plate 14.

According to a peculiarity of the invention, before the step d) of inserting the assembly 10 inside the bath of the first cell 9, a step g) of applying the above first substrate 2 in the second electrically conductive material on the active surface 7 of the matrix 6, or on the second substrate 2, will be provided.

The first substrate 5 will be also electrically connected with the nanowires 3 to define a charge collector integral thereto.

Substantially, the assembly 10 will be constituted by the first substrate 5, the matrix 6 and possibly by the second substrate 2.

The positioning of the first substrate 5 may be obtained by means of chemical or physical processes.

As an example, a step h) may be provided for insertion of the assembly 10 in a second electrolytic cell 15 containing a second solution with predetermined concentration of the second material, preferably copper.

As an example, the portion of the matrix 6 made conductive by the second substrate 2 may be placed into contact relationship with an electrolytic solution containing copper (II) salt.

By this way, the electrolytic deposition of copper may be obtained on the second substrate 2, through potentiostatic or galvanostatic reduction of the salts thereof, to define a substantially continuous first substrate 5 with thickness s₂ greater than the thickness Si of the second substrate 2, as already specified above, so that the material of the second substrate 2 will be at least partly embedded into the one of the first substrate 5.

Advantageously, the deposition process of the first substrate 5 and of the second substrate 2 may be carried out with the same electrolytic cell 9, after substitution of the electrodeposition baths.

Alternatively to the chemical process, the first substrate 5 may be a film of copper applied to the surface 7 of the matrix 6 by lamination adhesion.

In such a case the support structure will not be necessarily provided with the second substrate 2 and the above step b) may be not provided.

The step b) of deposition of the second substrate 2 may be also carried out by chemical or physical known processes.

By way of example a physical process may be provided for sputtering a first metal material, such as gold, platinum or palladium or the like, on the exposed surface of the support structure, carried out by means of a common sputter coater, not shown, as already disclosed in the above cited Italian application RM2008A000341.

Alternatively, a process may be provided for the electrochemical deposition of the second material by redox reaction thereof without supplying electric current. The second material may be selected in the group comprising tin, palladium, copper and the like.

To this end, a process of activation of the surface 7 of the matrix 6 by means of a suitable reducing agent may be provided.

This latter may be of the inorganic type, in a non limiting example iron (II) salt, tin (II) salt and the like, or organic, such as aldheyde, e.g. formyl aldheyde, alcohol, e.g. methyl alcohol, and the like.

Then, the process of reaction between the reducing agent and at least one salt of the metal to be deposited will be carried out.

As a consequence, the growing of the nanowires 3 will be obtained directly on a support defined only by the first substrate 5 or by the assembly of the two substrates 2 and 5, by electrochemical processes of deposition of a first and of a second material selected in the respective groups above indicated with reference to the electrode 1 of the present invention.

By way of example, it could be used an electrolytic bath with electrolytic solution, water- based or not, containing:

- at least one tin salt comprised between those whose anion is a sulphate or alkyl sulphate, one between the halide or the halogenated, a nitrate or one of the phosphates; this salt will operate as precursor of the metal tin;

- at least one of the salt of the metals of the already cited fourth group of the periodic table of the elements whose anions may be selected between the sulphate or alkyl sulphate, one between the halide or the halogenated, a nitrate or one of the phosphates; this salt will operate as precursor of the elements designed for the alligation with the first material, e.g. with the metal tin;

- at least one between sodium, potassium or ammonium salt, selected between those whose anion is a sulphate or alkyl sulphate, a halide or a halogenated, a nitrate or a phosphate, defining the support electrolyte, whose aim is to help the process of co- deposition of the metal species;

- at least one of the inorganic acids such as sulfuric or alkyl sulfonic acid, hydrohalic or halide acids, nitric acid, phosphoric and boric acid or an inorganic base such as sodium, potassium or ammonium hydroxide, for regulating the pH of the electrolytic solution;

- at least one chelating or leveling agent specifically acting on the deposition of the alloy to make it amorphous and selected between simple carbohydrate such as glucose, fructose, galactose, mannitol and other monosaccharide, or dimers such as sucrose, maltose, lactose, cellobiose and other disaccharide, or still some derivates thereof from controlled oxidation such as gluconates and generally for the salts and the esters of the aldonic and aldaric acids.

In case of manufacturing of nanowires 3 of tin-based alloys, by means of solutions containing one of the above tin salts, their composition may have a concentration of such salts between 0,001 M and 1 ,5 M in Sn (II).

The concentration of the salt of the metals of the fourth period of the table of chemical elements may be preferably comprised between 0,001 M and 4 M. The composition of the support electrolyte will be preferably comprised between 0,1 M and 2 M. The composition of the chelating or leveling agent will be preferably comprised between 0,001 M and 2 M.

In particular, it could be used carbohydrates with a concentration variable between 0,001 and 0,5 M, an acid average pH, comprised between 1 ,0 and 5,0.

Thus, properly adjusting the selection of the carbohydrate, of the concentration thereof and of the pH of the solution, it will be possible to modify the crystallographic nature of the deposition, its composition and, thus, the attended performances of this material, particularly when it is used as anode in rechargeable Li-Ion batteries.

It has also been noticed that these compounds have shown tendency to interact in a preferred way with Sn during the growing step, limiting the tendency to form crystal depositions.

To this aim it is also possible using compound such as urea, thiourea, EDTA and the like.

The growing process by electrodeposition may be carried out for a time comprised between 10min and 90min, at a temperature comprised between 20°C and 60°C.

Moreover a sequence of several consecutive electrodepositions may be provided each executed for a predetermined time, not necessary equal for each single electrodeposition, e.g. each for 60min.

In case of potentiostatic deposition there will be a voltage (E) comprised between -0,5V (SCE) and -1 ,6V (SCE).

The manufacturing process of the electrode will end with a removing step f) of the nanoporous support structure 6 to allow the nanowires 3 associated to the first 5 and possibly to the second substrate 2, i.e. of the electrode 1 , to be pull up, so to obtain a surface to be exposed to the reaction environment, constituted by the surfaces of the nanowires 3, extremely wide.

The removing step f) may provide the destruction of the support structure 6 by means of its controlled dissolution in water-based solutions of inorganic substances, e.g. sodium or potassium hydroxide, orthophosphoric acid, or in organic solvents, such as trichloromethane.

Examples of composition of the solution:

Example 1 : amorphous binary tin base alloy.

A solution has been used of 20 mM SnS0₄, 5 mM C0SO₄, 0,2 M Na₂S0₄, 0,1 M sucrose, pH 4,0, temperature 40 °C, with potentiostatic deposition at E -0,80 V(SCE), for a growing time of 60 minutes.

The deposition has been grown in an anodic alumina matrix 6, after manufacturing the copper current collector 5.

The dissolution of the matrix 6 has been carried out with potassium carbonate (KOH) at a temperature of 60 °C, for a time of 30 minutes.

Example 2: binary tin base alloy.

A solution has been used of 20 mM SnSO₄, 10 mM CuSO4, 0,05 M (NH₄)₂SO₄, 0,5 M fructose, 0,2 M boric acid, pH 2,5, temperature 60 °C, with potentiostatic deposition at E = -1 ,0 V(SCE) for a growing time of 60 minutes.

The deposition has been grown in a polycarbonate matrix 6 and after the copper collector 5 has been manufactured in a electrochemical way.

The dissolution of the matrix 6 has been carried out with trichloromethane at 25°C, for a time of 5 minutes.

Example 3: amorphous ternary tin base alloy.

A solution has been used of 10 mM SnCI₂, 10 mM FeCI₃, 5 mM ZnCI₂, 1 ,0 M KCI, 0,2 M sodium gluconate, pH 3,8, temperature 25 °C, with galvanostatic deposition with current intensity (j) = -0,7 mA cm^"2, for a growing time of 30 minutes.

The deposition has been grown in a policarbonate matrix 6, after manufacturing the copper current collector 5.

The dissolution of the matrix 6 has been carried out in dichloromhetane at 25 °C, for a time of 5 minutes.

The above electrode may be used both in Li-ion and Li-polymer accumulators, or in specific Li-ion accumulators wherein the liquid electrolyte is replaced by a conductive electrolyte covering one or both the active materials of the battery (anode e cathode), or by using a monomer (precursor of the polymer) introduced with the electrolyte that is thermally polymerized upon the battery assembling.

As matter of fact an accumulator with a SnCo nano-structured anode, having high specific capacity, may allow realizing a thin and lightweight Li-polymer accumulator, able to feed enhanced electronic devices, such as tablet, new generation smartphones, and may be used in space probes or drones for military objects.

In case of using these accumulators for automotive or, in any case, for feeding devices requiring a greater power amount it is possible to provide their series or parallel assembly.

A further use of the electrode of the invention may be in Li-air accumulators wherein the lithium anode may interact with a cathode defined by the oxygen in the atmosphere.

In such accumulators the anode always operates by oxidation with the oxygen until it is active and then it is mechanically replaced when the performances reduces under a predetermined threshold value.

The above disclosure clearly shows that the invention fulfills the intended objects and particularly of providing a nano-structured electrode with high structural stability and having high power density, in a non limiting example with theoretical capacity of 994 Ah/kgsn, as a method for manufacturing an electrode using nanowires firmly connected to the current collector in such a manner to increase its performances, particularly in terms of electric capacity, also being more lightweight relative to electrodes with the same features.

The method and the electrode of the invention are susceptible to a number of changes and variants within the inventive concept of the appended claims. While the method and the electrode have been disclosed with particular reference to the annexed drawings, the reference numbers are only used in the description and claims for the sake of a better intelligibility and shall not be intended as a limitation top the scope of the claimed invention.

Claims

1. A method for manufacturing a nano-structured electrode, comprising the following steps:

- providing a nano-porous matrix (6) having at least one active surface (7) and a plurality of substantially cylindrical pores (8) with diameter of nanometric size;

- providing a first electrolytic cell (9) containing an electro-deposition bath comprising a first electrolytic solution containing metallic salts;

- coupling of a first substrate (5) in a first electrically conductive material to said active surface (7) of said matrix (6);

- immersing said active surface (7) coupled to said first substrate (5) into said first electrolytic cell (9);

- growing nanowires (3) in a metal alloy of said salts inside said cylindrical pores (8); characterized in that said growing step of said nanowires comprises a feeding step with a potentiostatic or galvanostatic current to promote the growing of the nanowires directly on said first substrate (5) and to define a nano-structured charge collector, a step of removing said nano-porous matrix (6) from said collector being also provided to realize the electrode.

2. Method as claimed in claim 1 , characterized in that said coupling step of said first substrate (5) comprises an immersion step (h) of at least said active surface (7) in a second electrolytic cell (15) containing a solution of said first electrically conductive material, said first conductive material being applied to said matrix by potentiostatic or galvanostatic electrolytic deposition.

3. Method as claimed in claim 1 or 2, characterized by comprising, before said coupling step of said first substrate, a deposition step on said active surface of a second substrate (2) in a second electrically conductive material to realize an electric contact, said second substrate (2) being distributed on said first substrate (5) in a discontinuous manner to allow the direct contact of said nanowires (3) with this latter.

4. Method as claimed in claim 3, characterized in that said deposition step (b) of said second substrate (2) is carried out by a method selected between the sputtering and the redox reactions without feeding any electric current.

5. Method as claimed in claim 3 or 4, characterized in that said second substrate (5) is applied on said first substrate (2) by lamination of a film of said second electrically conductive material.

6. Method as claimed in any preceding claim, characterized in that said first electrically conductive material is selected into the group comprising the copper.

7. Method as claimed in claims 3 and 6, characterized in that said second material of said second substrate (2) is selected among the metals having electric conductibility at least equal to that of said first material.

8. Method as claimed in any preceding claims, characterized in that said first electrolytic solution comprises a chelating agent selected into the group comprising simple or dimer carbohydrates.

9. Method as claimed in any preceding claims, characterized in that said nano-porous matrix (6) comprises a membrane made of a base material selected among the ceramic materials, such as alumina, titanium oxide or the like, or among the polymeric materials, such as polycarbonate, PET or the like.

10. A nano-structured electrode, characterized in that it is constituted by:

- a plurality of nanowires (3) in a metallic alloy adapted to chemically interact with an electrolyte for transporting electric charges;

- a first substrate (2) in a first electrically conductive material electrically connected and in direct contact with at least part of the wires (3) to define a nano-structured electric charge collector;

- a possible second substrate (2) electrically conductive and electrically into contact with said nanowires (3) and said first substrate (2), said second substrate (2) being interposed therebetween and having discontinuous distribution to allow the direct contact of at least part of said nanowires (3) with said first substrate (5).

1 1. Electrode as claimed in claim 10, characterized in that said second substrate (2) has a thickness (si) between 10nm and 40nm and preferably between 20nm and 30nm, and said first substrate (5) has a thickness (s₂) between 1 μηι and 20μιη and preferably about 15μΐη.

12. Electrode as claimed in claim 10 or 1 , characterized in that said nanowires (3) have diameter between 10nm and 400nm and length between 1 μηι and 70μηι.

13. Electrode as claimed in any claims 10 to 12, characterized in that said metallic alloy comprises a first metallic or metalloid material selected among the group including tin, aluminium, silicon, germanium and a second metallic material selected among the metals of the fourth period of the periodic table of the chemicals elements.