Electrochemical cell

Abstract

An electrochemical cell comprising a cavity (2) containing an anode (3) and a cathode (4) immersed in an electrolyte (5) and separated by a diaphragm (6). The diaphragm (6) comprises at least one mica-based operative layer (7).

Description

[0001] ELECTROCHEMICAL CELL

[0002] The present invention relates to an electrochemical cell.

[0003] In several areas of technology it is common to use electrochemical cells that have a common configuration, according to which two electrodes are immersed in a tub containing an electrolyte and are separated by a porous diaphragm (or membrane, or, in any case, a separator).

[0004] For example, such a configuration is adopted in electrolytic cells (or electrolyzers), which make it possible to convert electricity to chemical energy by way of a process of electrolysis, for the production of hydrogen.

[0005] The diaphragm is not conductive to electrons (so as to prevent electrical shorting between the electrodes), but it can be passed through by the hydroxide ions produced by the chemical reaction of electrolysis. Furthermore, the presence of the diaphragm prevents the crossover of oxygen and hydrogen, which are produced respectively by the cathode and the anode.

[0006] In particular, among the various types used on an industrial scale, electrolyzers are known which use an alkaline electrolyte (which are sometimes referred to in the literature of the sector with the acronym AWE, Alkaline Water Electrolysis) in which the electrolyte that is used is an aqueous hydroxide solution, usually of potassium (KOH) or of sodium (NaOH).

[0007] The advantages of AWE electrolyzers are associated with the low capital cost required, long lifetime, and reliability.

[0008] In the past, diaphragms for AWE electrolyzers were usually made of asbestos, a material that today has been abandoned owing to a range of technical limitations; over time in fact, diaphragms have emerged which are made of porous synthetic alkali-resistant polymer films, for example such as polysulphone, which however requires the use of mineral fillers (like zirconium oxide, ZrO2or titanium dioxide, TiO2) or modification of the structure, owing to the high hydrophobic properties it would otherwise exhibit.

[0009] Also widely used are diaphragms based on perforated polyethylene films while, recently, more advanced solutions have been provided in which the diaphragm comprises a film of Ultra High Molecular Weight Polyethylene (sometimes referred to with the acronym UHMWPE).

[0010] The use of UHMWPE for producing microporous film makes it possible to obtain a high percentage of pores with respect to the volume of the film, with an average diameter of the pores of 2.6-2.7 nm. This gives diaphragms that use such technology an electrical conductivity that is higher than that obtainable with other materials, and this parameter is evidently of primary importance in that it directly influences the specific productivity of the cell, meaning the cost of the electric power necessary to produce one kilogram of hydrogen, with constant applied voltage and constant electrolyte concentration.

[0011] In any case, these are electrical conductivity values that do not sufficiently meet the needs of the market that increasingly often demands hydrogen, in particular for use as fuel in a plurality of different applications, in any case characterized by the absence of pollutant emissions or exhaust.

[0012] Another known limitation consists in that diaphragms for AWE cells made with synthetic microporous films are of high cost.

[0013] Similar problems are found in other sectors, in which electrochemical cells are used in the configuration outlined in the foregoing pages, and in which the diaphragm, placed to separate the electrodes, must in any case ensure maximum conductivity of ions but minimum conductivity of electrons.

[0014] The aim of the present invention is to solve the above-mentioned problems, by providing an electrochemical cell that has a diaphragm that ensures a particularly high specific electrical conductivity, higher than that obtainable with the known solutions.

[0015] Within this aim, an object of the invention is to provide an electrochemical cell that has a diaphragm that ensures high electrical conductivity of ions but minimum conductivity of electrons.

[0016] Another object of the invention is to provide a cell that is of low cost.

[0017] Another object of the invention is to provide a cell that ensures a high reliability of operation.

[0018] Another object of the invention is to provide a cell that adopts an alternative technical and structural architecture to those of conventional cells.

[0019] Another object of the invention is to provide a cell that is certain to be safe in use.

[0020] Another object of the invention is to provide a cell that can be easily obtained using elements and materials that are readily available on the market.

[0021] This aim and these and other objects which will become better apparent hereinafter are achieved by a cell according to claim 1 and by the uses thereof explained in the dependent claims.

[0022] Further characteristics and advantages of the invention will become better apparent from the detailed description that follows of a preferred, but not exclusive, embodiment of the electrochemical cell according to the invention, which is illustrated by way of non-limiting example in the accompanying drawings wherein:

[0023] Figure 1 is a partially cross-sectional front elevation view of the cell according to the invention;

[0024] Figure 2 is a greatly enlarged and cross-sectional detail of the cell of Figure 1;

[0025] Figure 3 is a block diagram of a vehicle comprising a cell according to the invention;

[0026] Figures 4 and 5 are block diagrams that illustrate respectively a method and a process for producing a cell according to the invention.

[0027] With reference to the figures, the reference numeral 1 generally designates an electrochemical cell, which comprises a cavity 2 containing an anode 3 and a cathode 4 immersed in an electrolyte 5 and separated by a diaphragm (or membrane, or separator) 6. In the discussion below, reference will sometimes be made to the “electrodes” of the cell 1, and this term means the anode 3 and the cathode 4.

[0028] The basic configuration of the cell 1 outlined above is common in the background art and is used in various technological contexts; the following pages will set out different applications and various implementation details relating to them, but it should be noted from this point onward that:

[0029] - any implementation choice, particularly but not exclusively relating to electrodes and the electrolyte 5, should be understood as covered in the scope of protection claimed herein;

[0030] - any use of the cell 1 should be understood as covered in the scope of protection claimed herein;

[0031] - over and above the peculiarities that will be illustrated below (in particular, but not exclusively, in relation to the diaphragm 6), any element of the cell 1 can be provided by the person skilled in the art drawing on the common general knowledge of the sector.

[0032] According to the invention, therefore, the diaphragm 6 comprises (or is constituted by) at least one mica-based operative layer 7. In particular, the mica can be chosen (preferably but not necessarily) from muscovite mica and phlogopite mica.

[0033] As is known, micas are a group of aluminosilicate minerals which can have different chemical compositions but which all share a stratified structure: as shown in Figure 2, mica crystals are constituted by superimposed elementary layers 8 that are substantially flat and of equal thickness (0.658 nm), separated from each other by interspaces or gaps 9, also of equal thickness (0.336 nm).

[0034] The interspaces 9 are permeable to Newtonian fluids with molecular or ionic dimensions of less than 0.336 nm and it is precisely this property that is exploited in a peculiar and innovative manner in the invention: the choice to provide the diaphragm 6 with at least one mica-based operative layer 7 makes it possible to make the diaphragm 6 non-conductive for electrons (so as to prevent electrical shorting between the electrodes), but particularly conductive for ions (which can travel along the interspaces 9), to the point of obtaining a particularly high specific electrical conductivity, higher than that obtainable with conventional solutions, and so achieving from this point onward the set aim.

[0035] The operative layer 7 can be passed through by one or more through holes 7a, which place the electrodes in communication.

[0036] In the present discussion, the term “mica-based” therefore means that the operative layer 7 has a composition that comprises mica in a quantity, configuration and / or structure that are such as to give the operative layer 7 (and the diaphragm 6) the peculiarities indicated above, which are indeed typical of mica.

[0037] The mechanical adhesion forces between the adjacent elementary layers 8 are weak, and therefore it is a relatively simple matter to separate these elementary layers 8, so obtaining plates (or flakes) with flat and parallel surfaces, which are referred to as “mica splittings”. After splitting, the surfaces of the plates can bond firmly to each other by virtue of the intermolecular forces of interaction (cohesion forces).

[0038] As is known, such plates have an elongated and arbitrary shape, and a size that can vary from 0.5 cm2to 50 cm2(or larger), with a thickness of 10- 45 pm. They are typically processed in order to separate them from mineral impurities and contaminated or damaged pieces, and they are divided into nine standard sizes.

[0039] More precisely, as is known the term "mica splittings” refers to a thin plate of mica, obtained by manually splitting large natural mica crystals, as well as by means of thermomechanical and hydromechanical methods of splitting small mica crystals. Owing to their natural properties, "mica splittings" plates have surfaces that are almost perfectly flat and parallel. The surface dimensions and thickness of mica splittings plates are governed by conventional standards.

[0040] The operative layer 7 is, as mentioned, mica-based, which can be in the form of mica splittings plates (of any size).

[0041] In a different embodiment, but still of significant practical interest, the operative layer 7 is, as mentioned, mica-based, which can be in the form of preferably non-impregnated mica paper (or micaceous paper).

[0042] As is known, mica paper is constituted by several sheets of mica splittings plates, which are bonded together without impregnation owing to intermolecular adhesion forces (cohesion forces). Mica splittings plates of mica paper are further compressed mechanically by means of rollers, so as to reach the necessary mechanical traction strength.

[0043] Basically, mica paper can be obtained with various different manufacturing techniques, starting from flakes or mica splittings plates without binder material.

[0044] The thermo / hydromechanical technique entails a preliminary treatment of the mica crystals (typically muscovite mica) at high temperature (900-960 °C), followed by a chemical treatment with a weak hydrochloric acid solution, which levigates the diamond- shaped mica crystals, eliminating the water of crystallization.

[0045] In the second technique phlogopite mica is typically used, and the flat crystals in this mica swell up easily at low temperatures: they are subsequently split in a machine called a “hydrosplitter” and therefore are split along interplanar bonds, to obtain mica pulp.

[0046] The mica pulp is then treated so as to form a film that effectively constitutes mica paper and which is wound in spools.

[0047] In any case, the different types of mica described up to this point and the related techniques of manufacturing mica paper are already known to the person skilled in the art and are moreover set out in the international standard IEC 60371-3-2.

[0048] The mica used to provide the diaphragm 6 can also be obtained by recycling discards or offcuts of mica paper.

[0049] In a configuration of significant practical interest, illustrated in Figure 2 for the purposes of non-limiting example of the invention, the diaphragm 6 comprises a plurality of operative layers 7, which have respective superimposed through holes 7a; furthermore, the operative layers 7 are arranged so that the holes 7a of each pair of adjacent operative layers 7 are mutually offset, with respect to the direction of passing through the diaphragm 6 from the anode 3 to the cathode 4, or vice versa. Preferably, in this case each operative layer 7 is constituted by a mica splittings plate.

[0050] Thus, there is no direct straight connection passing between the electrodes: the ions are forced to pass through the interspaces 9 between adjacent elementary layers 8 and in the channels 10 between one operative layer 7 and the next. To move from one electrode to the other, they are thus forced to follow a convoluted, “zigzag” path.

[0051] The applicant has verified that this choice makes it possible to appreciably increase the specific electrical conductivity, by making a prototype according to the diagram of Figure 1 and which adopts the configuration outlined above, shown in Figure 2. Figure 1 moreover also shows laminas 3a and 4a (for example made of copper) for supplying current, associated with the electrodes.

[0052] The electrodes can be made of any material, while remaining within the scope of protection claimed herein, but in an embodiment of significant practical interest, either or both of the anode 3 and the cathode 4 (or each one of them) is made of carbon fiber fabric.

[0053] In addition to the cell 1 described up to this point, which can be provided in any manner, the protection claimed herein also relates to a method 100 and a process 200 for producing a cell 1 according to what is described in the foregoing pages. The method 100 for producing the cell 1 is substantially of the hydromechanical type and entails, first of all, in a step a', preparing a suspension of mica in distilled water.

[0054] The mica can be (preferably) in the form of mica splittings plates, with flat and parallel surfaces, with a thickness of from 2 to 5 pm and surface area of from 5 to 25 mm2.

[0055] The suspension contains mica for 15-20% by volume (with respect to the total volume of the suspension) and distilled water for 80-85% by volume (with respect to the total volume of the suspension).

[0056] When it is put in water, the mica paper is converted very rapidly to a water-mica suspension, which can thus be effectively used in manner explained here.

[0057] Subsequently, the method 100 entails, in a step b', pouring the suspension prepared in step a' onto a metallic ribbon that has a plurality of orifices, so as to allow the draining of the water through these orifices and to deposit a kind of raw sheet uniform, composed of mica plates, on the metallic ribbon. The step b' can be executed, while the suspension is kept under constant agitation, by means of a dosage device based on the sprayer principle.

[0058] The step b. makes it possible to drain most of the water that was originally in suspension, in order to obtain the raw sheet.

[0059] The method 100 therefore entails introducing the metallic ribbon with the raw sheet into an evaporation oven, in turn maintained at a temperature that increases progressively from an entry section, kept at a constant temperature value comprised between approximately 50° C and approximately 60° C, and an exit section, kept at a constant temperature value comprised between approximately 150° C and approximately 160° C.

[0060] This makes it possible to refine the removal of the water.

[0061] At the exit from the oven, the residual humidity content of the raw sheet can be checked and must not be above 3%. Subsequently, in a step d', the method 100 entails removing the micabased raw sheet from the metallic ribbon, using an adapted device.

[0062] Therefore, in a step e', the method 100 entails introducing the raw sheet between two mutually opposite sizing rollers that are preferably counter-rotating, for the sizing and compaction of the raw sheet up until a mica-based operative layer 7 is provided.

[0063] For example, the sizing rollers can have the same diameter, as mentioned opposite directions of rotation, a width equal to that of the raw sheet, and they can define between them a gap between 40 and 100 pm (into which the raw sheet is introduced). Preferably, the surface finish of the rollers is chosen to be of class 8.

[0064] After passing through the gap between the rollers, the desired operative layer 7 is thus obtained, and can be used (in the step f) for assembling or making a cell 1 and therefore the operative layer 7 thus obtained (taken individually or superimposing it on other layers) can be used as a diaphragm 6 for separation between an anode 3 and a cathode 4 immersed in an electrolyte 5 inside a cavity 2.

[0065] The operative layer 7 obtained with the method 100 can be used in a cell 1 used for producing hydrogen (by means of electrolysis), in a cell 1 used as a fuel cell, as a lithium ion or sodium ion battery, or as a supercapacitor (we will return to these specific uses of the cell 1 in the pages below).

[0066] The scope of protection claimed herein also includes a process 200 for producing the cell 1, which is also substantially of the hydromechanical type and entails, first of all, in a step a", preparing a suspension of mica in distilled water.

[0067] The mica can be in the form of flakes or plate or it can also be obtained from discards (or offcuts) of mica paper. Preferably, the mica is in the form of mica splittings plates. When it is put in water, the mica paper is converted very rapidly to a water-mica suspension, which can thus be effectively used in manner explained here.

[0068] This step also makes it possible to break down the discards in the original flakes or plates.

[0069] Subsequently, in a step b", the process 200 entails pouring the suspension prepared in step a” onto a first ribbon, which can be unwound from a first drum, so as to deposit a raw patina of suspension on the first ribbon. The first ribbon can be made of carbon and preferably is made of carbon fibers, activated or non-activated.

[0070] The quantity of distilled water in the suspension can be chosen as a function of the implementation of the step b". In particular, the latter step can be performed by means of a dosage by weight, which is to be preferred to dosage by spraying (using a "shower" machine) in that it makes it possible to use less water and because it is of lower cost. Dosage by weight entails a uniform application over time of a certain mass of suspension of mica in distilled water onto the first ribbon; subsequently, using a scraper the raw patina can be leveled over the entire width of the above-mentioned first ribbon. In this way a very dense suspension is obtained, which reduces the time necessary for drying and the consumption of distilled water.

[0071] Therefore, the process 200 entails, in a step c", applying a second ribbon on the suspension, in order to define a composite ribbon comprising the first ribbon, the suspension (the raw patina), and the second ribbon.

[0072] The second ribbon can also be made of carbon and preferably is made of carbon fibers, activated or non-activated. Furthermore, it can be unwound from a respective second drum.

[0073] Subsequently, the process 200 entails, in a step d", introducing the composite ribbon between two mutually opposite squeezing rollers, for the removal of water and a first, preliminary calendering.

[0074] Then, in a step e", the process 200 entails introducing the composite ribbon into an evaporation oven maintained at a temperature that increases progressively from an entry section, kept at a constant temperature value comprised between approximately 50° C and approximately 60° C, and an exit section, kept at a constant temperature value equal to approximately 160° C.

[0075] Then, in a step f, the process 200 entails introducing the composite ribbon between two compaction rollers, for the final compaction of the composite ribbon, which is thus given a thickness that can be chosen as a function of the needs and / or of the requirements of the customer / commissioning client.

[0076] The two squeezing rollers preferably rotate in mutually opposite directions (they are counter-rotating); preferably the two compaction rollers also rotate thus; the diameter of all the rollers and the cleaning class of their surfaces is preferably chosen so as to not exceed the admissible traction force for the mica between the ribbons while still ensuring the necessary mechanical compression force for the final calendering.

[0077] In a step g", the composite ribbon treated in the previous step can thus be used as the anode 3 (constituted by either the first ribbon or the second), the diaphragm 6 (the sheet of mica, preferably of mica splittings plates, compacted and dried between the first ribbon and the second) and the cathode 4 (the other one of either the first ribbon or the second) of an electrochemical cell 1. In this manner moreover, the first ribbon and the second ribbon, as well as acting as electrodes, can also act as conductors of current.

[0078] Such a cell 1 can be used for producing hydrogen or as a supercapacitor (as will be seen in more detail below). Especially when the cell is to be used as a supercapacitor, the first ribbon and the second ribbon can be made of a fabric made of activated carbon fibers enriched with carbon nanotubes, so as to appreciably increase the specific surface of the fabric made of carbon (up to 2400-2600 m2 / g or higher) and therefore the specific capacity of the cell 1 used as a supercapacitor.

[0079] In order to obtain such a material, powder based on carbon nanotubes can be applied uniformly, before executing the step f", so that the powder is fixed in the volume of the first ribbon and / or of the second ribbon, between the carbon fibers, during compaction, and does not increase the thickness.

[0080] The composite ribbon obtained progressively in output from the compaction rollers can also be wound and stored, awaiting use in the cell 1, around a drum, preferably provided with an electric servomotor with a sliding clutch, so as to subject it to constant tension as the thickness of the composite ribbon being wound increases.

[0081] Usefully, the process 200 can entail, in a step h” subsequent to the step g”, verifying the humidity content of the composite ribbon, which preferably should be comprised between 3% and 5%.

[0082] Advantageously, the process 200 can entail, in a step i” subsequent to the step g” (and executed in any order with respect to the step h"), verifying the thickness of the composite ribbon.

[0083] Checking the thickness can preferably be performed by a contactless device, for example using ultrasound sonar technology, which makes it possible to verify the thickness of the first ribbon, of the second ribbon and of the mica interposed between them.

[0084] As already anticipated, the cell 1 can be used in any context and for any practical purpose, where the peculiar exploitation of the properties of mica, explained above, should be deemed of interest.

[0085] In any case, below some particular uses of the cell 1 are described, which effectively are also an object of the protection claimed herein.

[0086] First of all therefore, protection is claimed herein for the use of an electrochemical cell 1 according to the foregoing description, and wherein preferably the electrolyte 5 is of the alkaline type, for making hydrogen.

[0087] That is, effectively, the cell 1 can be an electrolytic cell (or electrolyzer) and be used to convert electricity to chemical energy through electrolysis, for the production of hydrogen.

[0088] The electrolyzer that comprises or is constituted by the cell 1 is characterized therefore by the presence of one or more superimposed micabased operative layers 7, which, preferably, are in the form of mica splittings or non-impregnated mica paper. This makes it possible to significantly increase the specific productivity of hydrogen in the alkaline electrolyte 5, understood both as specific productivity PE (energy productivity) of the cell 1 for the minimum consumption of electricity, and as specific productivity Pv (productivity by volume) of the cell 1 at its minimum volume, for the production of 1 kg of hydrogen.

[0089] In particular, the electrolyte 5 can be an aqueous solution of KOH and the diaphragm 6 is designed to be passed through by hydroxyl ions OH": the diaphragm 6 uses the peculiar properties of mica to ensure high specific electrical conductivity and therefore a corresponding and significant increase in the productivity of hydrogen.

[0090] It should be noted that in order to maximize the performance of the cell 1 it is necessary for the through holes 7a to be as small as possible and at the same time for the specific electrical conductivity of the diaphragm 6 (which works for example with a specific alkaline electrolyte 5) to be as high as possible. These concepts are mutually contradictory, in that the small flow area of the through hole 7a results in a small quantity of ions passing through and, as a consequence, a decrease in the number of gaseous hydrogen molecules obtained as a result of the electrolysis reaction. The solution consists in adopting a configuration like that of Figure 2, in which the percentage of holes 7a increases with the minimum possible transverse cross-section in the volume of the diaphragm 6.

[0091] In the prototype, the electrodes have the same thickness of 0.2 mm and the same area of 40x48 mm2; they are furthermore made of the same material: fabric made of non-activated carbon fibers with a thickness of 0.2 mm. The diaphragm 6 is constituted by two operative layers 7 of nonimpregnated mica paper with a total thickness of 80 pm.

[0092] The supply of current to the electrodes is provided by a copper lamina 50 pm thick, positioned so as not to interfere with the output of gas generated at the electrodes.

[0093] With battery voltages of 5 V and 6 V, the performance of the cell 1 was measured and the results are given in the table below, where they are shown in comparison with some conventional solutions.

[0094] It should be noted therefore that the cell 1 according to the invention makes it possible to obtain a production of hydrogen that is considerably higher than that of known solutions. Further tests have been conducted by the applicant using a cell 1 with an area of electrodes of 19.2 cm2: in a time of 120 seconds, with the voltage of 4.7 V to the electrodes and a current of 0.635 A through the cell 1, a volume of hydrogen of 9,080 mm3was obtained. By increasing the current it is possible to obtain higher values, for example equal to 10,351 mm3with a current equal to 1.61 A.

[0095] It is believed that with a cell 1 provided with seven diaphragms 6 in parallel, each one 20x20cm2, it is possible to obtain a maximum of 64 ml of hydrogen. In a specific use of significant practical interest, the use is envisaged of the (electrolytic) cell 1 for the production of hydrogen to supply power to a drive unit of a vehicle.

[0096] In this context, Figure 3 is a block diagram showing a possible mode of use of the cell 1 as an electrolyzer in a hybrid electric vehicle 20. Protection is therefore also claimed on such an electric vehicle, which comprises the cell 1.

[0097] The cylinder 21 contains hydrogen for reliably starting the (internal combustion) hydrogen engine 22; the hydrogen engine 22 is mechanically connected to a generator 23, which produces electricity. Part of this electricity is supplied to the electrolyzer 1 in order to produce sufficient hydrogen to make the hydrogen engine 22 operate at a given power level.

[0098] Most of the electricity is transferred to the traction engine 24 which is responsible for turning the wheels 25 of the vehicle 20.

[0099] In parallel to the traction engine 24, the vehicle 20 is provided with a battery 26 and a supercapacitor 27, which are configured for a short-term "boost" mode, when the rated power is not sufficient.

[0100] Distilled water is supplied continuously to the electrolyzer 1 from a tank 28, while the hydrogen engine 22 is in operation.

[0101] The possibility is not ruled out of using hydrogen (and the electrolytic cell 1) in another manner, while remaining within the scope of protection claimed herein.

[0102] Protection is also claimed herein for the use of a cell 1 according to what is described up to this point, and wherein preferably the electrolyte 5 is of the alkaline type, for the production of electricity.

[0103] That is, effectively, the cell 1 can be a fuel cell and be used (in an opposite manner to the previously described electrolyzer ) to convert chemical energy to electricity.

[0104] It must be noted that the use of an alkaline electrolyte 5 makes it possible to release only water vapor into the atmosphere, with no polluting effect, and therefore a fuel cell is obtained which is environmentally friendly.

[0105] The same materials can be used for both electrodes, for example materials that comprise carbon (carbon fibers and fabrics, carbon nanotubes, graphene).

[0106] The use of the diaphragm 6 makes it possible to significantly increase the specific ionic permeability, compared to known solutions, when a liquid electrolyte 5 is used.

[0107] The fuel cell that comprises or is constituted by the cell 1 is characterized therefore by the presence of one or more superimposed micabased operative layers 7, which, preferably, are in the form of mica splittings or non-impregnated mica paper. This makes it possible to significantly increase the specific electric power of the fuel cell.

[0108] Protection is also claimed herein for the use of an electrochemical cell 1 according to what is described up to this point, and wherein the electrolyte 5 contains lithium salts, in a lithium ion battery.

[0109] In more detail, the electrolyte 5 can comprise lithium salts dissolved in an aprotic organic solvent.

[0110] In other words, protection is also claimed herein for a lithium ion battery that comprises or is constituted by the cell 1 described in the foregoing pages.

[0111] The pack of electrodes can be positioned in a sealed accommodation with those electrodes connected to the ends of a current collector.

[0112] The migration of ions between the electrodes occurs during the charging / discharging phase.

[0113] The electrodes can be made of any material, and can include solutions that are already known in the background art.

[0114] In particular, the cathode 4 can be made of lithium- cobalt, of lithiumnickel-manganese-cobalt oxide, of lithium-nickel-manganese-cobalt- aluminum oxide, of lithium-manganese, of iron-lithium phosphate, or of lithium titanate.

[0115] In turn, the anode 3 can be made of carbon (in carbon fabric).

[0116] In this context, the mica-based diaphragm 6 makes it possible to ensure:

[0117] - maximum ionic conductivity between the electrodes in the volume of the battery during the charging / discharging phase,

[0118] - minimum electronic conductivity in order to reduce self-discharge currents,

[0119] - good mechanical properties, which offer the necessary electrical resistance of the diaphragm 6 with a low thickness of the operative layer 7,

[0120] - chemical inertia for the electrolyte 5 and the materials in the electrodes.

[0121] These results are in particular obtained with a diaphragm 6 that comprises one or more operative layers 7 of mica splittings or mica flakes / plates or mica paper (preferably non-impregnated).

[0122] The lithium ion battery (or accumulator) that comprises or is constituted by the cell 1 is characterized therefore by the presence of one or more superimposed mica-based operative layers 7, which, preferably, are in the form of mica splittings or non-impregnated mica paper. This makes it possible to significantly exceed the performance of conventional solutions and to reduce the recharging time.

[0123] Protection is also claimed herein for the use of an electrochemical cell 1 according to what is described up to this point, and wherein the electrolyte 5 contains sodium salts, in a sodium ion battery.

[0124] The migration of ions between the electrodes occurs during the charging / discharging phase.

[0125] In more detail, the electrolyte 5 can comprise sodium salt solutions in single or meso aprotic solvents (an aprotic solvent is a solvent in which the molecules, after cleavage, are not capable of forming H+ions).

[0126] In any case the use is envisaged of electrolytes 5 that comprise salt solutions in ionic liquids and also electrolytes 5 that comprise polymeric materials.

[0127] In other words, protection is also claimed herein for a sodium ion battery that comprises or is constituted by the cell 1 described in the foregoing pages.

[0128] As is known, sodium ion batteries are currently of great interest, owing to the worldwide scarcity of lithium reserves and the safety problems associated with its mining.

[0129] A sodium ion battery uses sodium ions (Na+) instead of lithium ions (Li+), which move between the electrodes (passing through the diaphragm 6, in the case discussed here).

[0130] The electrodes can be made of any material, and can include solutions that are already known in the background art.

[0131] In particular, the cathode 4 can be made with oxides, materials based on saline systems, and numerous organic compounds.

[0132] For the anode 3, materials based on carbon can be used.

[0133] By virtue of the use of the diaphragm 6, it is possible to obtain results similar to those shown above for lithium ion batteries, and therefore:

[0134] - maximum ionic conductivity between the electrodes in the volume of the battery during the charging / discharging phase,

[0135] - minimum electronic conductivity in order to reduce self-discharge currents,

[0136] - good mechanical properties, which offer the necessary electrical resistance of the diaphragm 6 with a low thickness of the operative layer 7,

[0137] - chemical inertia for the electrolyte 5 and the materials in the electrodes.

[0138] These results are in particular obtained with a diaphragm 6 that comprises one or more operative layers 7 of mica splittings or mica flakes / plates or mica paper (preferably non-impregnated).

[0139] The sodium ion battery (or accumulator) that comprises or is constituted by the cell 1 is characterized therefore by the presence of one or more superimposed mica-based operative layers 7, which, preferably, are in the form of mica splittings or non-impregnated mica paper. This makes it possible to significantly exceed the performance of conventional solutions and to reduce the recharging time.

[0140] Protection is also claimed herein for the use of an electrochemical cell 1 according to what is described up to this point, and wherein the electrolyte 5 is preferably chosen from among an aqueous electrolyte 5, an organic electrolyte 5 and an ionic liquid, in a supercapacitor. For an aqueous electrolyte 5, in particular a solution of H2SO4, KOH, Li2SO4or Na2SO4can be used.

[0141] In other words, protection is also claimed herein for a supercapacitor that comprises or is constituted by the cell 1 described in the foregoing pages.

[0142] In the supercapacitor, energy is accumulated as a result of the formation of a double electric layer at the interface between the electrode and the electrolyte 5. During the charging phase, the randomly distributed ions in the electrolyte 5 move toward the electrode of opposite polarity, under the effect of an electrical field.

[0143] The electrodes of the cell 1, when used in a supercapacitor, can be made of carbon, and in particular there is the possibility (preferred but not limiting the invention) of making electrodes of carbon fabric, filled with carbon nanotubes inserted between the carbon fibers of the fabric.

[0144] In this context, the mica-based diaphragm 6 makes it possible to ensure:

[0145] - maximum ionic conductivity between the electrodes in the volume of the battery during the charging / discharging phase,

[0146] - minimum electronic conductivity in order to reduce self-discharge currents,

[0147] - good mechanical properties, which offer the necessary electrical resistance of the diaphragm 6 with a low thickness of the operative layer 7,

[0148] - chemical inertia for the electrolyte 5 and the materials in the electrodes.

[0149] The supercapacitor that comprises or is constituted by the cell 1 is characterized therefore by the presence of one or more superimposed micabased operative layers 7, which, preferably, are in the form of mica splittings or non-impregnated mica paper. This makes it possible to appreciably exceed the characteristics of conventional supercapacitors and to reduce the recharging time.

[0150] The diagram of Figure 1 can be effectively adopted, for example, for a cell 1 used as an electrolyzer, but also for a cell 1 used as a supercapacitor, if the holes 11 are removed, as in the former case the holes are used for the outflow of hydrogen gas and oxygen and for the supply of distilled water.

[0151] In practice it has been found that the cell 1 according to the invention fully achieves the set aim, in that the use of a diaphragm 6 that comprises at least one mica-based operative layer 7 ensures a particularly high specific electrical conductivity, higher than that obtainable with conventional solutions. Such diaphragm 6 ensures high electrical conductivity of ions but minimal conductivity of electrons.

[0152] In all the above applications, it should be emphasized that the use of mica is environmentally friendly and does not produce damaging effects for nature or humans. The material that makes up the diaphragm 6 can in fact be broken down again into plates or flakes without any chemical reaction and without creating potentially pollutant discarded material.

[0153] The invention, thus conceived, is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. Moreover, all the details may be substituted by other, technically equivalent elements.

[0154] In the embodiments illustrated, individual characteristics shown in relation to specific examples may in reality be substituted with other, different characteristics, existing in other embodiments.

[0155] In practice, the materials employed, as well as the contingent dimensions and shapes, may be any according to requirements and to the state of the art. Where the technical features mentioned in any claim are followed by reference numerals and / or signs, those reference numerals and / or signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference numerals and / or signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference numerals and / or signs.

Claims

CLAIMS1. An electrochemical cell comprising a cavity (2) containing an anode (3) and a cathode (4) immersed in an electrolyte (5) and separated by a diaphragm (6), characterized in that said diaphragm (6) comprises at least one mica-based operative layer (7).

2. The electrochemical cell according to claim 1, characterized in that the mica is chosen from muscovite mica and phlogopite mica.

3. The electrochemical cell according to claim 1 , characterized in that the mica is in a form chosen between mica splittings plates and mica paper.

4. The electrochemical cell according to one or more of the preceding claims, characterized in that said diaphragm (6) comprises a plurality of said operative layers (7), provided with respective holes (7a) and mutually superimposed, said holes (7a) of each pair of adjacent said operative layers (7) being mutually offset, with respect to the direction of passing through said diaphragm (6) from said anode (3) to said cathode (4), or vice versa.

5. A method for producing a cell (1) according to one or more of claims 1-4, which entails the following steps of: a', preparing a suspension of mica in distilled water, b'. pouring the suspension prepared in said step a' onto a metallic ribbon that has a plurality of orifices, with consequent draining of the water through the orifices and the depositing on the metallic ribbon of a raw sheet of mica, c'. introducing the ribbon with the raw sheet into an evaporation oven maintained at a temperature that progressively increases from an entry section, kept at a constant temperature value comprised between approximately 50° C and approximately 60° C, and an exit section, kept at a constant temperature value comprised between approximately 150° C and approximately 160° C, d'. removing the mica-based raw sheet from the ribbon, e'. introducing the raw sheet between two mutually opposite sizingrollers, for sizing and compacting the raw sheet until a mica-based operative layer (7) is provided, f. using the operative layer (7) as a diaphragm (6) for separation between an anode (3) and a cathode (4) immersed in an electrolyte (5) inside a cavity (2), in order to provide the electrochemical cell (1).

6. A process for producing a cell (1) according to one or more of claims 1-4, which entails the following steps of: a" . preparing a suspension of mica in distilled water, b". pouring the suspension prepared in said step a' onto a first ribbon, c” applying a second ribbon on the suspension, in order to define a composite ribbon comprising the first ribbon, the suspension and the second ribbon, d” introducing the composite ribbon between two mutually opposite squeezing rollers, for the removal of water and a first, preliminary calendering; e". introducing the composite ribbon into an evaporation oven maintained at a temperature that progressively increases from an entry section, kept at a constant temperature value comprised between approximately 50° C and approximately 60° C, and an exit section, kept at a constant temperature value equal to approximately 160° C, f introducing the composite ribbon between two compaction rollers, for the final compaction, g” using the composite ribbon as anode (3), diaphragm (6) and cathode (4) of an electrochemical cell (1) according to one or more of claims 1-4.

7. The process according to claim 6, characterized in that said first ribbon and / or said second ribbon are made of carbon and preferably said first ribbon and / or said second ribbon are made of carbon fibers, activated or non-activated.

8. The process according to claim 6 or 7, characterized in that itentails, in a step h” subsequent to said step g”, verifying the humidity content of the composite ribbon.

9. The process according to one or more of claims 6-8, characterized in that it entails, in a step i” subsequent to said step g”, verifying the thickness of the composite ribbon.

10. Use of an electrochemical cell (1) according to one or more of claims 1-4, wherein said electrolyte (5) is preferably of the alkaline type, for producing hydrogen.

11. The use according to claim 10, for making hydrogen to supply power to a drive unit of a vehicle.

12. Use of an electrochemical cell (1) according to one or more of claims 1-4, wherein said electrolyte (5) is preferably of the alkaline type, for producing electricity.

13. The use of an electrochemical cell (1) according to one or more of claims 1-4, wherein said electrolyte (5) contains lithium salts, in a lithium ion battery.

14. The use of an electrochemical cell (1) according to one or more of claims 1-4, wherein said electrolyte (5) contains sodium salts, in a sodium ion battery.

15. The use of an electrochemical cell (1) according to one or more of claims 1-4, wherein said electrolyte (5) is preferably chosen from among an aqueous electrolyte (5), an organic electrolyte (5) and an ionic liquid, in a supercapacitor.

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