METHOD AND APPARATUS FOR MONITORING SELF-DISCHARGE PHENOMENA OF ELECTROCHEMICAL CELLS

Description

METHOD AND APPARATUS FOR MONITORING SELF-DISCHARGE PHENOMENA OF ELECTROCHEMICAL CELLS DESCRIPTION TECHNICAL SECTOR The present invention relates to a method for monitoring self-discharge phenomena of electrochemical cells and to an apparatus for monitoring self-discharge phenomena of electrochemical cells. In particular, the present invention finds advantageous, but not exclusive, application in monitoring self-discharge phenomena of electrochemical cells to be assembled into one or more batteries, or optionally into one or more modules of one or more batteries, for a vehicle, particularly an automobile, to which the following description will explicitly refer without prejudice to its generality. Other applications could lie in the field of storage systems for various solutions, for example from renewable sources such as solar panels, wind power, hydroelectric power, etc. EARLY ART As is well known, lithium batteries, due to their high energy density, are increasingly enabling the implementation of electric vehicles in the automotive sector. In particular, lithium ions currently represent, from a chemical standpoint, the state of the art in the production of high-capacity batteries. A battery comprises a plurality of electrochemical cells. Optionally, a battery comprises a plurality of modules, each module comprising a plurality of cells. In particular, a battery used in the automotive sector can comprise tens, hundreds or thousands of cells. Each cell comprises a casing and a plurality of layers arranged inside the casing. The layers include at least two electrode layers (positive and negative, i.e., cathode and anode) and a separator layer interposed between the two electrode layers, and may include dozens of electrode layers and separator layers interposed between the electrode layers. There are different types of cells, such as cylindrical cells, pouch cells, prismatic cells. In particular, enveloped cells and prismatic cells have a first and second dimension (length and width), extending along a first and second direction orthogonal to each other, respectively, larger than a third dimension (thickness) extending along a third direction orthogonal to the first and second directions. The envelope of a enveloped cell comprises a multilayer envelope, while the envelope of a prismatic cell comprises a metal can. Conveniently, enveloped cells are externally shaped like an envelope (or bag), and prismatic cells are externally shaped like a prism, specifically a parallelepiped. Cells are subject to self-discharge phenomena. Specifically, over time, a cell tends to lose its charge (i.e., its state of charge, SoC), simultaneously decreasing its voltage, even when the cell is not being used, for example while it is in storage. In other words, cells tend to self-discharge. However, some cells exhibit abnormal self-discharge and are therefore considered defective. Specifically, these defective cells have a self-discharge value greater than the expected and / or acceptable self-discharge value. A possible cause of abnormal self-discharge is the presence of metallic contamination and / or damage to the separator, causing contact between the positive and negative electrodes and thus a short circuit. Typically, cells are analyzed after they are manufactured, for example while in storage, to detect any defective cells, i.e., cells exhibiting abnormal self-discharge. Specifically, the voltage of each cell is periodically measured to determine whether the cell's self-discharge value is greater than an expected and / or acceptable self-discharge value—that is, to determine whether the cell exhibits abnormal self-discharge and is therefore defective. Therefore, if a defective cell is detected, it can be discarded. Subsequently, the cells are assembled into one or more batteries, or optionally into one or more modules of one or more batteries. To this end, the cells are compressed orthogonally to their respective main faces to ensure optimal performance. However, some cells may exhibit abnormal self-discharge, and thus be considered defective, only after they have been assembled into one or more batteries, or optionally into one or more modules of one or more batteries. One possible cause is the presence of latent metallic contamination and / or latent damage to the separator, i.e. metallic contamination and / or damage to the separator that was already present but had not been detected, for example because it was small and not sufficient to cause contact between the positive and negative electrodes and therefore a short circuit. If a battery (or module) contains even just one defective cell, the entire battery (or module) must be discarded, with obvious economic and environmental disadvantages. Furthermore, if the battery (or module) containing one or more defective cells is mounted on vehicles that are already on the market, it may be necessary to carry out a recall campaign, with obvious economic and image disadvantages. DESCRIPTION OF THE INVENTION The aim of the present invention is to provide a method for monitoring self-discharge phenomena of electrochemical cells and an apparatus for monitoring self-discharge phenomena of electrochemical cells which are at least partially free from the drawbacks described above and, at the same time, are simple and economical to manufacture. According to the present invention, a method for monitoring self-discharge phenomena of electrochemical cells and an apparatus for monitoring self-discharge phenomena of electrochemical cells are provided as claimed in the independent claims that follow and, preferably, in any of the claims dependent directly or indirectly on the independent claims. The claims describe preferred embodiments of the present invention, forming an integral part of this specification. BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention, a preferred embodiment is described below, by way of non-limiting example and with reference to the attached drawings, in which: - Figure 1 is a schematic view of an apparatus and method according to a first embodiment of the present invention; and - Figure 2 is a schematic view of an apparatus and method according to a second embodiment of the present invention. FORMS OF IMPLEMENTATION OF THE INVENTION With reference to figures 1 and 2, the numeral 1 indicates an apparatus for monitoring self-discharge phenomena of electrochemical cells 2 according to the present invention. The apparatus 1, described in detail below, allows to implement a method for monitoring self-discharge phenomena of electrochemical cells 2 according to the present invention. The method comprises a plurality of phases, described in detail below. The method comprises a step a) of providing a plurality of electrochemical cells 2, wherein each cell 2 has a first dimension and a second dimension, extending along a first direction and a second direction orthogonal to each other, respectively, greater than a third dimension extending along a third direction orthogonal to the first direction and the second direction. Each cell 2 comprises a casing 3 and a plurality of layers arranged internally of the casing 3. The layers comprise at least a first electrode layer, at least a second electrode layer, and at least a first separator layer interposed between the first electrode layer and the second electrode layer. In particular, cells 2 include planar cells, which include cells having planar electrode plates (blanks). In particular, planar cells include pouch cells, in which the envelope 3 comprises a multilayer bag, and prismatic cells, in which the envelope 3 comprises a metal can. Conveniently, pouch cells are externally shaped like an envelope (or bag), and prismatic cells are externally shaped like a prism, particularly a parallelepiped. Conveniently, planar cells include so-called Z-folded cells (which can be enveloped cells or prismatic cells, depending on the envelope type 3), in which the electrode layers are arranged parallel to each other and the separator layer is arranged in a zigzag pattern between the electrode layers, thus being interposed between the electrode layers. Conveniently, one between the first electrode layer and the second electrode layer is a cathode layer, and the other between the first electrode layer and the second electrode layer is an anode layer. Preferably, each cell 2 comprises a third electrode layer (of the same type, i.e., cathode or anode, as the first electrode layer) and at least one second separator layer interposed between the second electrode layer and the third electrode layer. Conveniently, each cell 2 may comprise dozens of electrode layers and separator layers interposed between the electrode layers. The method comprises a step b) of arranging the cells 2 inside a container 4, wherein the pressure inside the container 4 is equal to a first pressure. In particular, container 4 (illustrated schematically in Figures 1 and 2) can have any shape and size. Conveniently, container 4 defines a chamber 5, which can have any shape and size, in which cells 2 can be housed, i.e., in which cells 2 can be arranged. In phase b), the pressure inside chamber 5 is equal to the first pressure. The method comprises a step c) of bringing the pressure inside the container 4 to a second pressure higher than the first pressure. Specifically, the pressure inside container 4, which houses the 2 cells, is brought to the second pressure, which is greater than the first pressure. In other words, the pressure inside container 4, which houses the 2 cells, is increased from the first pressure to the second pressure. Conveniently, container 4 is controlled so that the pressure inside container 4 equals the second pressure, which is greater than the first pressure. In step c), the pressure inside chamber 5 equals the second pressure. Conveniently, since cells 2 are arranged inside container 4 (specifically inside chamber 5) and the pressure inside container 4 (specifically inside chamber 5) is equal to the second pressure, then cells 2 are subjected to the second pressure which is equivalent to a compressive force on cells 2, specifically on the two faces (of cells 2) orthogonal to the third direction, i.e. the two faces (of cells 2) having the largest surface area. The method comprises a step d) of measuring a voltage of each cell 2 of the plurality of cells 2 to detect whether a self-discharge value of such cell 2 is higher than a predetermined threshold. Specifically, for each cell 2, a first voltage value is considered, such as a nominal voltage value or a previously measured voltage value, and a second voltage value is measured. Conveniently, the first voltage value will be greater than or equal to the second voltage value, and typically greater than the second voltage value. Conveniently, the self-discharge value of each cell 2 is related to the comparison between the first voltage value and the second voltage value, specifically the difference (e.g., measured in mV) between the first voltage value and the second voltage value. Preferably, the self-discharge value of each cell 2 is also related to the time interval (e.g., measured in days) between the first voltage value (i.e., a time associated with the first voltage value) and the second voltage value (i.e., a time associated with the second voltage value). For example, the self-discharge value of each cell 2 is the ratio of the difference between the above difference and the above time distance. Conveniently, the preset threshold corresponds to a maximum expected and / or acceptable self-discharge value. Conveniently, if the self-discharge value of a specific cell 2 is higher than the preset threshold, an anomalous self-discharge is detected for that cell 2, i.e. the self-discharge of that cell 2 is higher than expected and / or acceptable. Phase c) is preceding or at least partially contemporaneous with phase d), and phase d) is preceding a phase of assembling the cells (2) into one or more batteries. In particular, there is no temporal overlap between phase c) and phase d), or there is at least a partial temporal overlap between phase c) and phase d). In other words, when step d) is performed it is no longer true that the pressure inside container 4 is equal to the second pressure, i.e. the pressure inside container 4 is no longer equal to the second pressure, or there is a time interval in which step d) is performed and the pressure inside container 4 is equal to the second pressure. Phase d) is prior to a phase of assembling the 2 cells into one or more batteries (i.e. battery modules). In particular, when phase d) is performed the cells 2 are not (yet) assembled into one or more batteries, or optionally into one or more modules of one or more batteries. In other words, cells 2 will be (optionally) assembled into one or more batteries, or optionally into one or more modules of one or more batteries, following step d). Preferably, container 4 contains air and the first pressure is substantially equal to the ambient pressure. In particular, air is present inside chamber 5. Conveniently, the first pressure is essentially equal to the ambient pressure Pambr, i.e., the normal (or standard) atmospheric pressure defined as Pamb=101325 Pa. In other words, when cells 2 are placed inside container 4, cells 2 are housed in chamber 5, which contains air at a pressure equal to the ambient pressure. Conveniently, when the cells 2 are placed inside the container 4, i.e., housed in chamber 5, chamber 5 is in fluid communication with the environment outside the container 4. Therefore, the first pressure is substantially equal to the ambient pressure. Preferably, the cells 2 are introduced into the container 4 through an opening in the container 4 in direct fluid communication with, i.e., facing, the environment outside the container 4 in which air is present at a pressure equal to the ambient pressure. Conveniently, the second pressure is higher than the ambient pressure. In particular, when the pressure inside the container 4 is brought to the second pressure, chamber 5 is not in fluid communication with the environment outside the container 4. Preferably, container 4 comprises an autoclave and / or a hyperbaric chamber. In particular, container 4 is hermetically sealable with respect to the environment external to container 4. In other words, chamber 5 can be hermetically sealed with respect to the environment external to container 4. Conveniently, container 4 is hermetically sealed with respect to the external environment when the pressure inside container 4 is equal to the second pressure. Conveniently, chamber 5 can be horizontal or vertical. For example, chamber 5 is cylindrical with a horizontal or vertical axis. Optionally (Figure 2), step a) comprises providing at least one housing 6, wherein the cells 2 are housed in the at least one housing 6, and step b) comprises arranging the at least one housing 6 inside the container 4. In particular, the at least one housing 6 is configured to house the cells 2. For example, the at least one housing 6 comprises at least one box and / or at least one rack. In the non-limiting embodiment illustrated in figure 2, the at least one housing 6 is a plurality of boxes, in particular three boxes, in which the cells 2 are housed. Conveniently, if in phase a) the cells 2 are housed in at least one slot 6, in phase b) The at least one housing 6 may be arranged inside the container 4, in particular in the chamber 5. In other words, the cells 2 are arranged inside the container 4, in particular in the chamber 5, via the at least one housing 6 in which the cells 2 are housed. Preferably, step d) follows step c) and comprises the step of extracting a cell 2 from the container 4 before measuring the voltage of that cell 2. In particular, step c) precedes step d), meaning there is no temporal overlap between steps c) and d). In other words, when step d) is performed, it is no longer true that the pressure inside container 4 is equal to the second pressure, meaning the pressure inside container 4 is no longer equal to the second pressure. Conveniently, after step c) is performed, the pressure inside container 4 is decreased, preferably from the second pressure to the first pressure, and at least one cell 2 is extracted from container 4. Subsequently, the voltage of each cell 2 extracted from container 4 is measured. Preferably, the method comprises a step e), preceding step c), of measuring a voltage of each cell 2 of the plurality of cells 2, wherein step d) comprises comparing the voltages measured in step e) with the respective voltages measured in step d) to detect whether a self-discharge value of such cell 2 is higher than a predetermined threshold. In particular, phase e) is prior to phase c), and for example prior to phase b). In other words, when step e) is performed, the pressure inside container 4 has not yet been brought to the second pressure greater than the first pressure, and for example cells 2 have not yet been placed inside container 4. Conveniently, cells 2 are inside container 4, where the pressure inside container 4 is equal to the first pressure, or cells 2 are outside container 4. Conveniently, in step e), the aforementioned first voltage value is measured, which is a voltage value measured prior to step d), in which the second voltage value is measured. Conveniently, the self-discharge value of each cell 2 is related to the aforementioned comparison between the first voltage value, measured during step e), and the second voltage value, measured during step d), in particular taking into account any time gap between steps e) and d). Preferably, phase c) lasts longer than a predetermined period. In particular, the duration of phase c) is also monitored to avoid any cycle errors or detect equipment problems. Specifically, the pressure inside container 4 is brought to a pressure higher than the first pressure for a duration greater than the predetermined period, i.e., cells 2 are maintained inside container 4, where the pressure is equal to the second pressure, at least for the predetermined period. For example, the predetermined period is a number of days, such as two days. Preferably, the second pressure is between a first pre-set threshold and a second pre-set threshold. In particular, the second pressure, to which cells 2 are subjected and which is equivalent to a compressive force on cells 2, is greater than the first pre-set threshold and less than the second pre-set threshold. Preferably, the first predetermined threshold corresponds to a compressive force on the cells 2, specifically on the two faces (of the cells 2) orthogonal to the third direction, which is greater than or equal to a compressive force to which the cells 2 will be subjected, specifically on the two faces (of the cells 2) orthogonal to the third direction, when they are assembled into one or more batteries, or optionally into one or more modules of one or more batteries, and begin to be used. In other words, the first predetermined threshold corresponds to a compressive force on the cells 2, specifically on the two faces (of the cells 2) orthogonal to the third direction, which is greater than or equal to a compressive force to which the cells 2 will be subjected at the instant of the start of the life of the batteries. For example, the first pre-set threshold corresponds to a compressive force (in detail determined by the pressure inside container 4) on the 2 cells, in particular on the two faces (of the 2 cells) orthogonal to the third direction, which is equal to 2000 N. Conveniently, the second pre-set threshold corresponds to a compressive force on the 2-cells, in particular on the two faces (of the 2-cells) orthogonal to the third direction, which is smaller than a maximum compressive force that can be sustained by the 2-cells. Conveniently, the maximum compressive force that can be sustained by the 2-cells depends on the type of the 2-cells. Preferably, the method comprises the step of discarding each cell 2 such that the self-discharge value of such cell 2 is higher than the aforementioned predetermined threshold. In particular, if in phase d) it is detected that the self-discharge value of a specific cell 2 is higher than the preset threshold, that cell 2 is discarded, i.e. it is removed from the plurality of cells 2. Conveniently, that cell 2 is replaced with another cell 2. Figure 1 illustrates a non-limiting example of the method, in particular according to a first embodiment of the present invention. For example, a manufacturer of cells 2 is considered, i.e., the person who makes cells 2 to supply them to a user of cells 2. Conveniently, the unit of measurement of time (indicated on the time arrow) is one day. Specifically, cells 2 are manufactured on day 0, and left for four days without being compressed, for example while stored. On day 4, the aforementioned first voltage value of each cell 2 is measured (step e). On the following two days (days 5 and 6), cells 2 are placed inside container 4, where the pressure inside container 4 is equal to the first pressure (step b), and the pressure inside container 4 is brought to the second pressure greater than the first pressure (step c). On day 7, the aforementioned second voltage value of each cell 2 is measured (step d) to detect whether a self-discharge value of that cell 2 is higher than a predetermined threshold. Conveniently, if the self-discharge value of a specific cell 2 is detected to be higher than the predetermined threshold, that cell 2 is discarded, i.e., it is removed from the plurality of cells 2. In the non-limiting embodiment illustrated in Figure 1, step d) is performed after step c), i.e., step c) precedes step d). In particular, cells 2 are removed from container 4 before measuring the aforementioned second voltage value of each cell 2. However, step d) could be performed at least partially simultaneously with step c), i.e., step c) could be at least partially contemporary with step d), for example, the aforementioned second voltage value of each cell 2 could be measured when cells 2 are inside container 4 and are subjected to the second pressure. Figure 2 illustrates a non-limiting example of the method, in particular according to a second embodiment of the present invention. For example, a user of cells 2 is considered, i.e., someone who receives cells 2 from a cell manufacturer 2 for use. In particular, the cell user 2 receives from the cell manufacturer 2 at least one housing 6 in which the cells 2 are housed (step a). For example, the at least one housing 6 is a plurality of boxes, in particular three boxes, in which the cells 2 are housed. The at least one housing 6, in which the cells 2 are housed, is placed inside the container 4, wherein the pressure inside the container 4 is equal to the first pressure (step b), and the pressure inside the container 4 is brought to the second pressure higher than the first pressure (step c). Subsequently, a voltage value of each cell 2 is measured (step d) to detect whether a self-discharge value of that cell 2 is higher than a predetermined threshold. Conveniently, if it is detected that the self-discharge value of a specific cell 2 is higher than the preset threshold, that cell 2 is discarded, i.e. it is removed from the plurality of cells 2. In the non-limiting embodiment illustrated in Figure 2, step d) is performed after step c), i.e., step c) precedes step d). In particular, cells 2 are removed from container 4 before measuring the voltage value of each cell 2. However, step d) could be performed at least partially simultaneously with step c), i.e., step c) could be at least partially simultaneous with step d), for example, the voltage value of each cell 2 could be measured when cells 2 are inside container 4 and are subjected to the second pressure. Figures 1 and 2 show non-limiting examples of an apparatus 1 according to the present invention. The apparatus 1 comprises a container 4 configured to house a plurality of electrochemical cells 2 described above, and a detection system 7. In the non-limiting embodiments illustrated, cells 2 are pouch cells. The sensing system 7 is configured to measure a voltage of each cell 2 of the plurality of cells 2 to detect whether a self-discharge value of such cell 2 is above a predetermined threshold. Apparatus 1 is configured to assume a first configuration, in which the pressure inside container 4 is equal to a first pressure, and a second configuration, in which the pressure inside container 4 is equal to a second pressure greater than the first pressure. In particular, the first configuration is an introduction configuration, in which the cells 2 are introduced into the container 4 and are subjected to the first pressure, and the second configuration is a compression configuration, in which the cells 2 are inside the container 4 and are subjected to the second pressure greater than the first pressure. Conveniently, when the apparatus 1 is in the first configuration, the container 4 is open, in particular when the cells 2 are introduced into the container 4, and can subsequently be closed, in particular when the cells 2 are inside the container 4 and are subjected to the first pressure. Conveniently, when the apparatus 1 is in the second configuration, the container 4 is closed, in particular when the cells 2 are inside the container 4 and are subjected to the second pressure. Preferably, container 4 contains air and the first pressure is substantially equal to the ambient pressure. In particular, the fluid inside container 4, specifically chamber 5, is air, and the first pressure is substantially equal to the ambient pressure Pamb / i.e., the normal (or standard) atmospheric pressure defined as Pamb = 101325 Pa. In other words, when apparatus 1 is in the first configuration, cells 2 are subjected to a pressure equal to the ambient pressure. Preferably, when apparatus 1 is in the first configuration, cells 2 are introduced into container 4 through an opening in container 4 in direct fluid communication with, i.e., facing, the environment outside container 4, in which air is present at a pressure equal to the ambient pressure. Conveniently, the second pressure is greater than the ambient pressure. In particular, when apparatus 1 is in the second configuration, chamber 5 is not in fluid communication with the environment outside container 4. Preferably, container 4 comprises an autoclave. Specifically, the autoclave is an apparatus comprising a fixed part and a movable part that is movable relative to the fixed part. Conveniently, the fixed part of the autoclave is hollow and defines chamber 5, and the movable part of the autoclave is configured to define an open autoclave configuration, in which chamber 5 is in fluid communication with the environment outside the autoclave, and a closed autoclave configuration, in which chamber 5 is not in fluid communication with the environment outside the autoclave. Typically, the autoclave is not configured to house humans inside chamber 5. Preferably, container 4 comprises a hyperbaric chamber. Specifically, the hyperbaric chamber is an apparatus comprising a fixed part and a mobile part that is movable relative to the fixed part. Conveniently, the fixed part of the hyperbaric chamber is hollow and defines chamber 5, and the mobile part of the hyperbaric chamber is configured to define an open configuration of the hyperbaric chamber, in which chamber 5 is in fluid communication with the environment outside the hyperbaric chamber, and a closed configuration of the hyperbaric chamber, in which chamber 5 is not in fluid communication with the environment outside the hyperbaric chamber. Typically, the hyperbaric chamber is configured to also accommodate humans inside chamber 5. Preferably, the sensing system 7 comprises at least one voltage meter 8, configured to measure a voltage of each cell 2 of the plurality of cells 2, and a plurality of electrical contacts configured to be in contact with terminal poles 9 of the cells 2 and electrically connected to the at least one voltage meter 8. In particular, each cell 2 comprises at least two terminal poles 9 (positive and negative, i.e., cathode and anode) arranged on the same side of the cell 2, as in the non-limiting embodiments illustrated, or arranged on opposite sides of the cell 2. When the voltage of the cell 2 is measured, the cell 2 is electrically connected to the at least one voltage meter 8, since the two terminal poles 9 are in contact with the electrical contacts which are electrically connected to the at least one meter 8. Obviously, the number and arrangement of the terminals 31 may vary depending on the configuration of the cell 2 that one wishes to test (for example, a greater number of terminals may be present and / or these may be answered by different sides of the cell 2). Preferably, the voltage meter 8 is configured to be electrically connected to a plurality of cells 2 simultaneously. In particular, the two terminal poles 9 of each cell 2 of the plurality of cells 2 are in contact with electrical contacts that are electrically connected to the at least one voltage meter 8 via electrical cables. For example, voltage meter 8 is arranged outside container 4, so as to measure a voltage of each cell 2 of the plurality of cells 2 when the cells 2 are outside container 4. Additionally or alternatively, the voltage meter 8 can be housed inside the container 4, so as to measure a voltage of each cell 2 of the plurality of cells 2 when the cells 2 are inside the container 4. Advantageously, but not limited to, the detection system 8 is configured to be able to disconnect the electronic components (voltage meter 29, printed circuit board 34, detection unit 35) from the cells 2 during the self-discharge observation period. This prevents any passive absorption from affecting the measurement result. Conveniently, the sensing system 7 comprises a sensing unit 10 (illustrated schematically in Figures 1 and 2) communicatively coupled to the voltage meter 8 and configured to detect, for each cell 2, whether a self-discharge value of that cell 2 is greater than a predetermined threshold. From an examination of the features of the method and apparatus 1, the advantages of the present invention are evident. In particular, arranging the cells 2 inside the container 4, wherein the pressure inside the container 4 is equal to a first pressure, bringing the pressure inside the container 4 to a second pressure greater than the first pressure, and measuring a voltage of each cell 2 of the plurality of cells 2 to detect whether a self-discharge value of such cell 2 is higher than a predetermined threshold allows for the detection of any defective cells 2, i.e., cells 2 having an anomalous self-discharge, before the cells 2 are assembled into one or more batteries, or optionally into one or more modules of one or more batteries. The method also allows to detect any cells 2 that may exhibit an abnormal self-discharge only after they have been assembled into one or more batteries, or optionally into one or more modules of one or more batteries. In particular, the method also allows for the detection of latent metallic contamination and / or latent damage to the separator, i.e., metallic contamination and / or damage to the separator that were already present but were not detected, for example because they were minor. In fact, the step of increasing the pressure inside container 4 to the second pressure higher than the first pressure, which precedes the compression to which cells 2 will be subjected when assembled, causes the positive and negative electrodes to come closer together, potentially triggering a short circuit in the event of latent metallic contamination and / or latent damage to the separator. The method allows to detect any defective cells 2 without using mechanical devices that depend on the specific type of cells 2, for example on the shape and / or size of the cells 2. In fact, it is sufficient to arrange the cells 2 (or optionally arrange at least one housing 6 in which the cells 2 are housed) inside the container 4 and increase the pressure inside the container 4, in which the cells 2 are arranged, from the first pressure to the second pressure, and measure a voltage of each cell 2 of the plurality of cells 2 to detect whether a self-discharge value of such cell 2 is higher than a predetermined threshold. The compressive force on the cells 2, in particular on the two faces (of the cells 2) orthogonal to the third direction, can be easily controlled by acting on the pressure inside the container 4, in particular by acting on the second pressure. The method can be easily implemented by both a cell manufacturer 2 and a cell user 2. The apparatus 1 allows to easily implement the method and obtain its benefits, through the container 4 and detection system 7. In particular, the container 4 and the detection system 7 do not depend on the specific type of cells 2, for example on the shape and / or size of the cells 2. Method and apparatus 1 allow only the defective cells to be discarded instead of discarding the entire battery (or module) containing such defective cells, with obvious economic and environmental advantages. Furthermore, method and apparatus 1 allow to reduce the probability of carrying out a recall campaign, with obvious economic and image advantages. Finally, it is clear that modifications can be made to the method and apparatus 1 without departing from the scope of protection defined by the claims. LIST OF FIGURE REFERENCE NUMBERS apparatus cell casing container chamber housing detection system voltage meter terminal pole detection unit

Claims

1. A method for monitoring self-discharge phenomena of electrochemical cells, comprising the steps of: a) providing a plurality of electrochemical cells (2), wherein each cell (2) has a first dimension and a second dimension, extending respectively along a first direction and a second direction orthogonal to each other, greater than a third dimension extending along a third direction orthogonal to the first direction and to the second direction, wherein each cell (2) comprises a casing (3) and a plurality of layers arranged internally to the casing (3), wherein the layers comprise at least a first electrode layer, at least a second electrode layer and at least a first separator layer interposed between the first electrode layer and the second electrode layer; b) arranging the cells (2) inside a container (4), wherein the pressure inside the container (4) is equal to a first pressure;c) bringing the pressure inside the container (4) to a second pressure higher than the first pressure; d) measuring a voltage of each cell (2) of the plurality of cells (2) to detect whether a self-discharge value of said cell (2) is higher than a predetermined threshold, where step c) is preceding or at least partially contemporary with step d), and step d) is preceding a step of assembling the cells (2) into one or more batteries.; 2. Method according to claim 1, wherein the container (4) contains air and the first pressure is substantially equal to the ambient pressure.

3. Method according to claim 1 or 2, wherein the container (4) comprises an autoclave.

4. Method according to one of the preceding claims, wherein the container (4) comprises a hyperbaric chamber.

5. Method according to one of the preceding claims, wherein step a) comprises providing at least one housing (6), wherein the cells (2) are housed in the at least one housing (6), and step b) comprises arranging the at least one housing (6) inside the container (4).

6. A method according to one of the preceding claims, wherein step d) is subsequent to step c) and comprises the step of extracting a cell (2) from the container (4) before measuring the voltage of said cell (2).

7. a method according to one of the preceding claims, comprising a step e), prior to step c), of measuring a voltage of each cell (2) of the plurality of cells (2), wherein step d) comprises comparing the voltages measured in step e) with the respective voltages measured in step d) to detect whether a self-discharge value of said cell (2) is higher than a predetermined threshold.

8. Method according to one of the preceding claims, wherein step c) has a duration greater than a predetermined period.

9. Method according to one of the preceding claims, wherein the second pressure is between a first predetermined threshold and a second predetermined threshold.

10. Method according to one of the preceding claims, comprising the step of discarding each cell (2) such that the self-discharge value of said cell (2) is higher than said predetermined threshold.

11. Apparatus for monitoring self-discharge phenomena of electrochemical cells, comprising: - a container (4) configured to house a plurality of electrochemical cells (2), wherein each cell (2) has a first dimension and a second dimension, extending along a first direction and a second direction respectively, greater than a third dimension extending along a third direction orthogonal to the first direction and to the second direction, wherein each cell (2) comprises a casing (3) and a plurality of layers arranged internally to the casing (3), wherein the layers comprise at least a first electrode layer, at least a second electrode layer and at least a first separator layer interposed between the first electrode layer and the second electrode layer;and - a detection system (7) configured to measure a voltage of each cell (2) of the plurality of cells (2) to detect whether a self-discharge value of said cell (2) is higher than a predetermined threshold, wherein the apparatus (1) is configured to assume a first configuration, wherein the pressure inside the container (4) is equal to a first pressure, and a second configuration, wherein the pressure inside the container (4) is equal to a second pressure greater than the first pressure.; 12. Apparatus according to claim 11, wherein the container (4) contains air and the first pressure is substantially equal to the ambient pressure.

13. Apparatus according to claim 11 or 12, wherein the container (4) comprises an autoclave.

14. Apparatus according to one of claims 11 to 13, wherein the container (4) comprises a hyperbaric chamber. 5 15. Apparatus according to one of claims 11 to 14, wherein the sensing system (7) comprises at least one voltage meter (8), configured to measure a voltage of each cell (2) of the plurality of cells (2), and a plurality of electrical contacts configured to be 10 in contact with terminal poles (9) of the cells (2) and electrically connected to the at least one voltage meter (8).