WO2023156320A1

WO2023156320A1 - System and method for monitoring the state of health of an electric energy storage device, and electric energy storage device including said system

Info

Publication number: WO2023156320A1
Application number: PCT/EP2023/053431
Authority: WO
Inventors: Antonio De Renzis; Juri BELCARI
Original assignee: Marposs Societa' Per Azioni
Priority date: 2022-02-16
Filing date: 2023-02-13
Publication date: 2023-08-24
Also published as: TW202337732A

Abstract

System (7) and method for monitoring the state of health of an electrical energy storage device (1 ) comprising at least one cell (3) provided with a first electrode (4) and a second electrode (5) between which at least one layer of separator material (6) is interposed; the system comprises at least one detector (8) arranged within the cell, at least one enlightening element (12), with a light source arranged inside the cell, in proximity to the detector element, and at least one connection means (9) configured to transmit an output signal (OS) from the detector; wherein the detector is configured to detect at least one color or color variation in a detection zone (DZ) within the cell. The method comprises the step of determining an amount and/or a concentration variation of a chemical species (CS) in the cell by detecting such color or color variation.

Description

DESCRIPTION

"SYSTEM AND METHOD FOR MONITORING THE STATE OF HEALTH OF AN ELECTRIC ENERGY STORAGE DEVICE, AND ELECTRIC ENERGY STORAGE DEVICE INCLUDING SAID SYSTEM"'

TECHNICAL FIELD

The present invention relates to a system and a method for monitoring the state of health of an electric energy storage device. Furthermore, the present invention relates to an electric energy storage device including said system.

In particular, the present invention finds advantageous but not exclusive application in monitoring the state of health of planar or prismatic rechargeable batteries, for example for use in battery packs for electric or hybrid vehicles, to which the following description will make explicit reference without lose in generality.

BACKGROUND ART

Rechargeable batteries of many shapes and types are known. In the electric or hybrid car market, even more than in the consumer electronics market, it is becoming increasingly important to maintain the efficiency of the battery pack over the long term so as to guarantee the user certain long-term performances (for example in terms of autonomy) justifying the relevant expensive cost.

In addition to performance, an absolutely non-negligible aspect to be taken into account is the safety of the vehicle electric energy storage systems, i.e. the batteries forming the battery pack aboard a vehicle. In particular, the most commonly used batteries for these purposes (e.g. lithium ion batteries, lithium polymer batteries, lithium metal batteries, etc.) usually contain active materials that are highly flammable and/or explosive and/or radioactive and, therefore, avoiding the leakage of these materials or their overheating has become a priority objective in recent years.

Therefore, efficiency and safety are undoubtedly among the reasons that push the automotive market to monitor as best as possible the state of health of battery packs (of the modules that make it up, or even of the individual cells) intended for use on vehicles.

Currently, monitoring the safety and efficiency of vehicle battery packs is assigned to systems known in the field as BMSs (Battery Management Systems).

A BMS may feature one of many different configurations and architectures which can be selected according to the type of application and/or the preferred monitoring strategy. In any case, the physical quantities that are monitored and measured (at a general, module or cell level) are substantially always the same, namely: current, voltage and temperature.

In recent years, numerous attempts have been made to improve the detections carried out by the BMSs or to combine the detected quantities so as to be able to identify an ever increasing number of malfunctions. However, not all the types of malfunctions inside the battery packs can be detected by checking the three aforementioned physical quantities and therefore, in some cases, the BMS belatedly or never reports a malfunction.

Furthermore, the voltage, current and temperature measured represent the result of chemical processes inside the batteries, which, before showing a voltage or current variation detectable by a BMS, or causing a considerable increase in temperature, can potentially propagate, in each cell, from one layer to the other.

Therefore, the detection of malfunctions inside the battery packs is in many cases late and/or incomplete.

Furthermore, what is detected by a BMS (for example a voltage drop) may be the result of malfunctions of different kinds. In this case, it is impossible to distinguish the specific malfunction and consequently improve the production process of the batteries.

DISCLOSURE OF THE INVENTION

The object of the present invention is to provide a system and a method for monitoring the state of health of an electric energy storage device and a related storage device, which are at least partially free from the drawbacks described above and, at the same time, can be obtained in an easy and economic way.

In accordance with the present invention, a system and a method for monitoring the state of health of an electric energy storage device and a related electric energy storage device are provided according to what is claimed in the independent claims that follows and, preferably, in any of the claims directly or indirectly depending from the independent claim.

The claims describe preferred embodiments of the present invention forming an integral part of the present description

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the attached drawings, which illustrate some non-limiting embodiments thereof, in which:

- Figure 1 illustrates, schematically and with details removed for clarity, a perspective and exploded view of a possible embodiment of an electric energy storage device in accordance with the present invention;

- Figures 2 and 3 show side and schematic views, with details removed for clarity, of two different embodiments of a system in accordance with the present invention; and

- Figures 4 and 5 illustrate schematically and with details removed for clarity, perspective views of the device of figure 1 in two different operating conditions.

BEST MODES FOR CARRYING OUT THE INVENTION

In Figure 1 , reference number 1 indicates an electric energy storage device as a whole. In particular, the electric energy storage device 1 is rechargeable.

The same reference numbers and letters in the figures identify the same elements or components having the same function.

In the context of this description, the term "second" component does not imply the presence of a "first" component. In fact, these terms are used as labels to improve clarity and are not to be understood in a limiting way.

The elements and features illustrated in the various preferred embodiments, including the drawings, can be combined with each other without departing from the scope of protection of the present application as described below.

In some non-limiting cases, the electric energy storage device 1 is a rechargeable - or secondary - battery, for example a lithium ion battery, a lithium metal battery, a lithium-sulphur battery, a flow battery, etc.

In other non-limiting cases, the electric energy storage device is a capacitor.

In the non-limiting embodiments of the attached figures, the electrical energy storage device 1 is of the planar type (in particular stacked), but obviously all the contents of the present application remain valid also for storage devices of a different type (for example "jelly roll", "z-fold", etc.), per se known and therefore not further detailed.

As illustrated in the non-limiting embodiments of figures 4 and 5, the device 1 preferably comprises a casing 2 (for example a so-called metal "can", or an envelope, in the case of batteries of the "pouch" type).

Furthermore, the device 1 comprises at least one cell 3, which is preferably arranged inside the casing 2. The cell 3 in turn comprises at least a first (layer of) electrode 4, a second (layer of) electrode 5 and a layer made of separating material, or separator 6, which is interposed between the electrode 4 and the electrode 5.

Advantageously but not necessarily, the cell 3 comprises further separators 6 and further electrodes 4, 5, interposed between each other. In particular, the cell 3 can be any type of cell for assembling batteries or capacitors of known type (for example a single cell, a bicell, a half-cell, etc., laminated or not). More specifically, the storage device 1 comprises a plurality of cells 3 interconnected to one another and, for example, stacked.

The device 1 further comprises a system 7 for monitoring the state of health of the device 1 . The wording "monitoring of the state of health" means checking at least one of those chemical-physical characteristics which determine or which are bound to the efficiency and safety of the storage device 1 .

As illustrated in the non-limiting embodiments of figures 1 to 3, the device 1 , or the monitoring system 7, comprises at least one detector element 8, which is configured to be arranged (inside the casing 2) in the vicinity (i.e. in correspondence) of the cell 3, or inside the cell 3.

According to some preferred non-limiting embodiments, the storage device 1 comprises a plurality of detector elements 8, in particular arranged, each, in correspondence of a respective cell 3. Preferably, with each cell 3 of the storage device 1 matches at least a respective detector element 8 (for example, in cases of cells 3 of considerable size, several detector elements 8 can be provided even for a single cell 3).

In particular, advantageously but not necessarily, the plurality of detector elements 8 is connected to a respective connection means 9 configured to transmit the output signal OS from the detector element 8. Preferably, the connection means 9 outgoing from cells 3 belonging to the same storage device 1 end up in a single, dedicated bus. In this way it is possible to considerably reduce the wiring inside the storage device 1 , so simplifying the management of the connections.

In the non-limiting embodiments of the attached figures, the connection means 9 is a cable (for example for electric data transmission). In other non-limiting and not illustrated embodiments, the connection means 9 comprises a wireless module which allows the detector element 8 to communicate without the need for a physical connection.

Advantageously, the detector element 8 is configured to detect at least one color and/or a color variation (in particular, at least one value, for example a numeric value, associated with a certain color and/or a certain color variation) of at least an element present in a detection zone DZ close to the detector element 8 (and schematically illustrated in figures 2 and 3). In other words, the detector element 8 is configured to detect or identify the color (and/or a variation thereof) of the element that surrounds it (for example an electrolyte 10) or which it faces (for example the separator 6 or one of the electrodes 4, 5). In particular, the detector element 8 is configured to detect the color of at least one chemical species CS present inside the cell 3. In other words, the detector element 8 is capable of detecting the colored components (i.e. it detects the composition of the color) of the chemical species CS present inside the cell; preferably, but not exclusively, the chemical species produced by the electrochemical reactions at the cathode.

In some non-limiting cases, such as those illustrated in figures 2 or 3, the detector element 8 faces one of the electrodes 4, 5. In other non-limiting cases, such as the one illustrated in figure 1 , the detector element 8 faces towards the separator 6.

Advantageously but not necessarily, the detector element 8 is immersed in the electrolyte 10 which is diffused inside the casing 2 and which permeates the separator 6.

According to some non-limiting embodiments, the detector element 8 is configured to detect the color (and/or a variation thereof) of a chemical species CS contained in the electrolyte 10. In other words, the detector element 8 is configured to detect the color and/or a color variation of the electrolyte 10.

Alternatively or additionally, the detector element 8 is configured to detect the color of a chemical species CS at one of the electrodes 4, 5. For example, as illustrated in figures 2 and 3 the electrode 4 (or 5) comprises at least a metallic support or core 20 and a coating 21 obtained by deposition of active material, the color of which (and/or a variation thereof) is detected (in the presence of a substantially transparent electrolyte) by the detector element 8. In other words, the detector element 8 is configured to detect the color and/or a color variation of the electrode 4, 5.

Alternatively or additionally, the detector element 8 is configured to detect the color (and/or a variation thereof) of a chemical species CS at the separator 6. In other words, the detector element 8 is configured to detect the color and/or a color variation of the separator 6.

In some non-limiting cases, such as those illustrated in figures 1 to 3, the detector element 8 comprises at least one photodiode 11 .

Advantageously but not necessarily, the detector element 8 comprises a number of photodiodes, for instance at least three photodiodes, each provided with a specific colored filter. In particular, the detector element 8 comprises (is) an RGB detector (of a known type and therefore not further detailed below).

The detector element 8 comprises a greater number of photodiodes 11 , for example nine photodiodes, provided with relative colored filters. The photodiodes 11 may alternatively comprise infrared filters.

In general, and as already mentioned above, detector elements 8 (or “detectors”) of this kind are essentially made up of a certain number of photodiodes with different optical colored filters wherein each individual photodiode responds with a different signal, substantially carrying a numeric value relating to the detected color. The signals provided by the different photodiodes are transmitted to a processing unit that, in case of a battery pack including a number of cells 3, like the one (18) schematically shown in figures 4 and 5, may be housed in casing 2 and be configured to receive the signals of the photodiodes 11 of the detector elements 8 of all the cells 3 of the battery pack. The signals of the photodiodes 11 of each cell 3 are combined in such a processing unit (not shown in the figures) so as to provide a signal, the output signal OS, comprising information on the color fingerprint of such cell 3. Such fingerprint is then analyzed and compared with a fingerprint corresponding to a state of good health of the battery, for instance in an external control unit 17. It is pointed out that these detectors provide for a simple serial interface and require a low consumption power supply, they do not require the intervention of a spectrometer, and, also in view of their extremely small dimensions, when used inside the cells 3 in an arrangement according to the present invention, provide excellent performance in detecting colors and color variations. The solution is thus extremely simple and economical, easy to be integrated within the cells, and in general of particularly flexible use, suitable for cells and battery packs of different types. It is also very easy, considering the serial interfaces, to arrange the detectors in series inside a battery pack.

Preferably, the system 7 further comprises at least one illuminating or enlightening element 12 with a light source, which is arranged in the vicinity of the detector element 8 and is configured to at least partially enlighten the detection zone DZ. Advantageously but not necessarily, the detector element 8 and the enlightening element 12 are integrated in the same support substrate 13. In other words, the detector element 8 and the enlightening element 12 are made on the same printed circuit, preferably with a substantially planar conformation or in any case having shape and dimensions allowing it to be geometrically coupled between the layers of the storage device 1 . In this way, it is possible to optimize the miniaturization of the detector element 8 and of the enlightening element 12, which is particularly important for allowing integration into already existing architectures of storage devices 1 .

In particular, advantageously but not necessarily, the system 7 (i.e. the assembly substantially formed by the enlightening element 12 and the detector element 8) has a substantially planar conformation which preferably occupies an area of less than 25 mm2, in particular it has a height and width less than 5 mm, especially less than 4 mm. Furthermore, preferably but not necessarily, the system 7 (i.e. the assembly substantially formed by the enlightening element 12 and the detector element 8) has a thickness of less than 3 mm, in particular less than 2 mm.

In some non-limiting cases, the detector element 8 and the enlightening element 12 are integrated in a single chip (i.e. in a single integrated circuit).

According to some non-limiting embodiments, the enlightening element 12 is a white illuminator 14 (for example with LED).

Alternatively or additionally, the enlightening element 12 is an infrared illuminator 14.

As illustrated in the non-limiting embodiment of figures 2 and 3, the system 7 also comprises a transparent case 15, inside which the detector element 8 is arranged. The case 15 is configured to protect the detector element 8 (and the enlightening element 12) from the chemical elements present inside the cell 3. In this way, the life of the detector element 8 is prolonged. In particular, the transparent case 15 incorporates the detector element 8. Preferably but not necessarily, the material with which the transparent case 15 is made is a resin.

Advantageously but not necessarily, as illustrated in the non-limiting embodiment of figure 3, the system 7 further comprises an amplifier (that is enhancer or magnifier) element 16, which is configured to enhance the color variations. The amplifier element 16 is arranged in the detection zone DZ and includes additives that affect its color in the presence of certain chemical reactions. In particular, the amplifier element 16 has a sheet-like shape and is arranged parallel to the electrodes 4, 5. The presence of the amplifier element 16, which does not disturb the normal electrochemical operation of the cell 3, is particularly advantageous, for example when the chemical species CS under observation is poorly colored or is in such a low concentration that color variations would be difficult to detect per se. The amplifier element 16 comprises for example a membrane which can be made of random fibers or nanofibers functionalized with additives.

According to some preferred non-limiting embodiments, the detector element 8 is arranged between the separator 6 and the electrode 4. In particular, the electrode 4 is a cathode of the electric energy storage device 1 .

Preferably, the system 7 also comprises a control unit 17, configured to determine, as a function of a color variation detected by the detector element 8, an amount and/or a concentration variation of the chemical species CS inside the cell 3, in particular at the electrode 4 (or 5), as illustrated for example in figures 2 and 3. In other words, the control unit 17 is connected via the connection means 9 to the detector element 8, allowing monitoring of the health status of the device 1 during its useful life. For example, the control unit 17 is a BMS or is integrated in a BMS and the connection means 9 is a monitoring bus of the device 1 .

In the non-limiting embodiment of figures 4 and 5 a vehicle battery pack 18 comprising two cells 3 is schematically shown. In particular, the cells 3 of the same battery pack 18 are monitored by the same control unit 17 which, for example, can be integrated into a BMS.

In particular, the control unit 17 is configured to monitor the state of health of the cells 3 and possibly disable, for example through the BMS in which it is integrated, the cell 3 that, based on the signals received from the detector element 8, has a risky or compromised state of health.

In some preferred non-limiting cases, the system 7 is entirely integrated within the device 1 .

Preferably, the system 7, in particular the detector element 8, is configured so as to be selectively activated. In particular, the detector element 8 can be periodically activated, to monitor any degradation of the state of health of the device 1 over time.

In accordance with a further aspect of the present invention, a method is provided for monitoring the health of an electric energy storage device as previously described.

In particular, the method includes the phases of:

- determining, by means of at least one detector element 8 arranged in correspondence of the cell 3, a quantity and/or a variation in concentration of a chemical species CS; and

- processing, based on the quantity and/or the variation detected by the detector element 8, the state of health of the electric energy storage device 1 .

In detail, the quantity and/or the variation in concentration of the chemical species CS is determined by detecting, by means of the detector element 8, at least one color or a variation thereof of an element (electrode, separator, electrolyte, etc.) present in the detection zone DZ. In particular, the detection zone DZ is an internal volume (or area) of the cell 3 at the main surface of an electrode 4, 5, preferably the main surface of the cathode.

Advantageously but not necessarily, the amount and/or the concentration variation of the chemical CS species is determined by associating a value with the intensity of the detected color (by the detector element 8) and comparing it (by means of the control unit 17) to the values of a table of predefined values or to a value corresponding to a previously detected color. In other words, in some non-limiting cases, the system 7 determines the amount of the chemical species CS (and also the presence, since an amount of zero indicates the absence of a certain chemical species CS featuring a given color) by comparing the intensity of the detected color with values of a consultation tables. In other non-limiting cases, the system 7 determines a variation value of the concentration of the chemical species CS by comparing the current color in the detection zone DZ with a previously detected color stored for example in a storage unit of the control unit 17. In particular, the check can take place by comparing the intensity of the individual RGB components that make up the analyzed color with the relative values stored in a correctly operating condition of the cell.

Advantageously but not necessarily, the method comprises the further step of enlightening at least partially the detection zone DZ during detection by the detector element 8. In other words, while the element 8 detects the color of an element (electrode, separator, electrolyte, etc.) present in the detection zone DZ, the enlightening element 12 illuminates or enlighten it, making the measurement more effective and precise.

Advantageously but not necessarily, the enlightening element 12 is dimmable, i.e. it is configured to allow the adjustment of the light intensity emitted by it. Thus, the effectiveness of detection by the detector element 8 can be maximized.

In some non-limiting cases, the luminosity of the enlightening element 12 is adjusted according to the type of cell 3 to be controlled (i.e. based on the technology of the storage device 1 ).

According to some non-limiting embodiments, the luminosity of the element 12 is adjusted according to the check to be carried out, that is depending on the chemical species whose concentration variation is to be detected.

Alternatively or additionally, the enlightening element 12 is configured to emit a light having an adjustable color. In particular, the enlightening element 12 comprises one or more colored LEDs (for example with an RGB combination), so as to adjust (even dynamically) the color of the light emitted by the enlightening element 12. In this way, it is possible to maximize the effectiveness of the detection by the detector element 8, adapting the wavelength of the light emitted by the enlightening element 12 to that which it is desired to detect.

Preferably, the detector element 8 detects the color of the electrode 4 (advantageously the cathode) or of the separator 6 or of the electrolyte 10. According to some preferred but non-limiting embodiments, the quantity and/or variation of the chemical species CS is checked periodically (for example at 30 second intervals), so as to constantly monitor the state of health of the cells 3 or in general of the device 1 or of the battery pack 18.

In particular, the method also includes the phases of:

- comparing the quantity and/or concentration variation of the determined chemical species CS with a predefined threshold value; and

- identifying at least one malfunction of the storage device 1 as a function of the exceeding (positively or negatively) of the predefined threshold value by the quantity and/or the concentration variation of the determined chemical species CS.

By way of example, some of the malfunctions that can be identified by the system 7 are mentioned hereinbelow.

In the case of the lead-acid batteries it is possible to determine a plurality of malfunctions, such as for example the rapidity of corrosion of the lead alloy electrode. In fact, such corrosion is influenced by the dissolution of ammonium oxide hydrate (Sb2OsxnH2O), the latter being characterized by a yellow colored chemical species.

It is also possible to determine the sulphation of the battery, since long periods of rest cause an acid stratification that is beige colored and therefore can be detected by the detector element 8. In particular, a certain amount of PbSO4 (that is beige in color) irreversibly accumulates, and this event can be worsened by oxygen infiltrations, which in the long run cause a short circuit in the battery.

In addition, it is possible to determine the degradation of the active positive material, as particles of PbO2 (a dark colored chemical species) are suspended in the electrolyte 10 making it increasingly dark.

In the case of lithium-sulfur batteries, it is thus possible to effectively determine the so-called "shuttle" effect of the polysulphides, since the color of the electrolyte 10 changes from substantially white to dark red.

In the case of lithium-cobalt batteries (LCO), it is thus possible to determine the degradation of the cathode (in particular of the active material, i.e. the coating 21 ) due to the interaction with the electrolyte 10. This reaction is exothermic and autocatalytic and its product is mainly CO3O4 (i.e. a black chemical species), which undergoes further reduction reactions from the electrolyte 10 into CoO, causing short circuits and/or explosions.

In the case of LMO batteries (lithium-manganese LiMn2O4 ion batteries), the level of corrosion of the cathode can be determined, such corrosion occurring due to the dissolution of manganese under different possible conditions that cause the formation of different chemical species having different colors such as pink colored MnF2 or green colored MnO.

In the case of NMC batteries (lithium-nickel-manganese-cobalt), it is possible to determine the drop in capacity at high voltage and degradation of the cathode at 80°C as they cause an irreversible formation of lithium-manganite (Li2MnOs, that is a chemical species reddish-brown in color). Furthermore, the migration from the cathode of species such as MnO (green colored) and MnF2 (pink colored) which are deposited on the anode surface is detectable.

Obviously, the malfunctions detectable by means of the system 7 are by no means to be understood as limited to what is described above.

In detail, the quantity and/or variation of the chemical species CS beyond a certain threshold - that is specific and variable according to the type of battery, its dimensions and its characteristics - indicate a malfunction of the device 1 . Therefore, the detector element 8, by detecting the color and/or the color variation corresponding to the presence and/or the concentration variation of the chemical species CS in excess of said threshold value, determines the signaling of an alarm.

As illustrated in the non-limiting embodiments of figures 4 and 5, the method preferably further comprises the additional step of disabling a cell 3 (in the case of figure 5 the cell 3 on the right), or an electric energy storage device 1 in a battery pack 18, in case that a malfunction is identified as described above.

In use, the control unit 17 controls the detector element 8 and the enlighting element 12 so as to activate them periodically and simultaneously and detect the color produced and/or the color variation produced by the chemical reactions inside the device 1 during the charge and discharge cycles. In particular, the quantity and/or concentration variation of certain chemical species are monitored: the presence of such chemical species may be completely harmless if they remain below certain threshold values, but can negatively affect the health of the cells if large quantities were reached. A clear example is the case of lithium-sulphur batteries, wherein the main electrochemical reaction that takes place at the electrodes during the proper operation generates colored chemical compounds/species. Even in this case the system and the method according to the present invention allow to distinguish between proper and abnormal operations by detecting not just the presence of such color of chemical/com pound species but a variation of its intensity beyond a predetermined threshold.

Although the above description makes particular reference to a very specific embodiment, the present invention is not to be considered limited to this embodiment. In fact, all those variants, modifications or simplifications covered by the attached claims fall within its scope of protection. Such variant may include, for example, a different type of detector element, a different location or conformation of the detector element, a different method of signaling the state of health or exclusion of the cells, etc.

The system, the device, the battery pack and the method described above have numerous advantages.

First of all, they allow to detect malfunctions and generate and transmit warning or error signals in much shorter times with respect to the devices that are currently used in electric or hybrid vehicles (for example the current BMS).

Furthermore, punctual and accurate monitoring is permitted, which also may allow to foresee future dangerous malfunctions of the individual cells before they can cause a degradation of the safety or in any case of the state of health of the battery pack.

A further advantage of the present invention lies in the possibility of distinguishing, by detecting specific color/s, between two or more different kind of malfunction which produce a same result as detectable by currently known systems, for example a voltage drop or a current or temperature peak.

In addition, what has been described up to now is applicable both to the current generation of batteries used in vehicles on the market and in stationary or portable energy storage systems (for example lithium-ion batteries), and to future generations of electric energy storage devices, such as lithium-sulfur or flow batteries. In any case, it is possible to use the system 7 in connection with electric energy storage devices 1 featuring any kind of architecture, that is prismatic, cylindrical, "pouch" batteries, etc.

Finally, the efficiency and safety of rechargeable batteries can be further improved, since it is possible to obtain a faster and more accurate feedback on what are the most common internal malfunctions, allowing to improve the production processes. The improvement is mainly due to the type of feedback (that is a detected color and/or a variation of the color that can be correlated to specific chemical species) and to the reaction time of the system (faster than the known BMS).

Claims

1. System (7) for monitoring the state of health of an electrical energy storage device (1 ) comprising at least one cell (3) provided with a first electrode (4) and a second electrode (5) between which at least one layer of separator material (6) is interposed; the system (7) comprising:

- at least one detector element (8) configured to be arranged in proximity to said cell (3);

- at least one connection means (9) configured to transmit an output signal (OS) from said detector element (8); the system (7) being characterized in that said detector element (8) is arranged inside said cell (3) and is configured to detect at least one color and/or a color variation of at least part of a detection zone (DZ) close to said detector element (8), the system also includes at least one enlightening element (12), with a light source arranged inside said cell (3), in proximity to said detector element (8), configured to at least partially enlighten said detection zone (DZ).

2. System (7) according to claim 1 , wherein said detector element (8) comprises at least one photodiode (11 ).

3. System (7) according to claim 2, wherein said detector element (8) comprises a number of photodiodes (11 ), each provided with a specific colored filter.

4. System (7) according to claim 3, wherein said detector element (8) comprises an RGB detector.

5. System (7) according to any one of claims 1 to 4, wherein said enlightening element (12) comprises a white LED.

6. System (7) according to any one of claims 1 to 5 and comprising a transparent casing, inside which the detector element (8) is arranged, configured to protect said detector element (8) from the chemical elements present inside the cell (3).

7. System (7) according to claim 6, wherein said transparent casing is made out in a resin and incorporates the detector element (8).

8. System (7) according to any one of claims 1 to 7 and comprising an amplifier element (16) arranged within said detection zone (DZ) and including additives that affect its color when certain chemical reactions take place.

9. Electric energy storage device (1 ) comprising:

- a casing;

- at least one cell (3) comprising in turn at least a first electrode (4), a second electrode (5) and a layer of separator material (6) interposed between the first electrode (4) and the second electrode (5); and

- at least one system (7) according to any one of claims 1 to 8.

10. Device (1 ) according to claim 9, wherein said detector element (8) is arranged between the separator (6) and one of said first electrode (4) and second electrode (5).

11 . Device (1 ) according to claim 10, wherein the first electrode (4) is a cathode, the detector element (8) being arranged between the separator (6) and the cathode.

12. Vehicle battery pack (18) comprising at least one electrical energy storage device (1 ) according to any one of claims 9 to 11 .

13. Method for monitoring the state of health of an electrical energy storage device (1 ) comprising at least one cell (3) provided with a first electrode (4) and a second electrode (5), between which at least one layer of separator material (6) is interposed; the method comprises the steps of:

- enlightening at least partially a detection zone (DZ) by means of at least one enlightening element (12), having a light source arranged inside said cell (3),

- determining, by means of at least one detector element (8) arranged inside the cell (3), a quantity and/or a variation in concentration of a chemical species (CS);

- processing, based on said quantity and/or variation detected by the detector element (8), the state of health of the electrical energy storage device (1 ); the method being characterized in that said quantity and/or variation in concentration of the chemical species (CS) is determined by detecting, by means of said detector element (8), at least one color and/or a color variation of at least part of a detection zone (DZ) inside said cell (3).

14. Method according to claim 13, wherein said quantity and/or variation of the chemical species (CS) is determined by associating a value with the intensity of the detected color and comparing it to the values of a table of predefined values or to a value corresponding to a previously detected color.

15. Method according to claim 13 or claim 14, wherein the detection zone (DZ) is enlightened at least by means of a white and/or infrared and/or colored LED.

16. Method according to any one of claims 13 to 15, wherein the detector element (8) detects the color and/or the color variation of one of said first electrode (4), second electrode (5) and separator (6).

17. Method according to any one of claims 13 to 15, wherein the detector element (8) detects the color and or the color variation of an electrolyte (10) in which the detector element (8) is plunged.

18. Method according to any one of claims 13 to 17, wherein the step of determining the quantity and/or the variation in concentration of the chemical species (CS) is periodically repeated.

19. Method according to any one of claims 13 to 18 and comprising the further steps of:

- comparing the determined quantity and/or variation in concentration of the chemical species (CS) with a predefined threshold value;

- identifying at least one malfunction of the storage device (1 ) as a function of the exceeding of said predefined threshold value by said determined quantity and/or variation in concentration of the chemical species (CS).

20. Method according to claim 19 and comprising the further step of disabling said cell (3) in the event that a malfunction is identified.