Method useful for controlling the non-oxidizing nature of the gaseous medium of an electrochemical device and in particular for detecting the undesirable presence of an oxidizing gas, electrochemical device and related use.

Abstract

Method useful for controlling the non-oxidizing nature of the gaseous medium of an electrochemical device and in particular for detecting the undesirable presence of an oxidizing gas therein, electrochemical device and related use The present invention relates to the use of an additional electrode based on at least one ionic, electroactive and oxidizable conductive element or material in an electrochemical device comprising at least one electrochemical cell comprising a positive electrode, a negative electrode and an electrolyte, as a means for detecting the presence or absence of an oxidizing gas in said electrochemical device, said additional electrode having a redox potential lower than that of said oxidizing gas. Figure for the abstract: None

Description

Title of the invention: Method useful for controlling the non-oxidizing nature of the gaseous medium of an electrochemical device and in particular for detecting the undesirable presence of an oxidizing gas, electrochemical device and related use. Technical field

[0001] The present invention relates to the field of electrochemical storage systems, more precisely the field of electrochemical devices of the accumulator or metal-ion battery type; lithium-sulfur or lithium-air batteries; and supercapacitors, for example potassium hybrid supercapacitors.

[0002] It aims more precisely to detect the presence of undesirable gas, in particular oxidizing gas, within an electrochemical device with at least one electrochemical cell.

[0003] Although described with reference to a Lithium-ion accumulator, the invention applies to any metal-ion electrochemical accumulator, i.e. also Sodium-ion, Magnesium-ion, Aluminum-ion...or more generally to any electrochemical accumulator and to supercapacitors.

[0004] The invention applies in particular to any geometry (cylindrical, prismatic, stacked) and any chemistry of metal-ion accumulators, such as for example NMC / Graphite, NCA / Graphite, NMC / G-Si, LFP / Graphite, LMO / LTO, Na-ion with non-aqueous electrolyte in liquid, gel or so-called solid electrolyte form. Prior art

[0005] As illustrated schematically in Figures 1 and 2, a lithium-ion battery or accumulator usually comprises at least one electrochemical cell C consisting of an electrolyte constituent 1, impregnated in a separator making it possible to electrically insulate the electrodes, a positive electrode or cathode 2, a negative electrode or anode 3, a current collector 4 connected to the cathode 2, a current collector 5 connected to the anode 3 and finally, a packaging 6 arranged to contain the electrochemical cell and make it sealed against the outside air and the electrolyte inside the cell, while being crossed by a part of the current collectors 4, 5.

[0006] The architecture of conventional lithium-ion batteries is an architecture that can be described as monopolar, because it has a single electrochemical cell comprising an anode, a cathode and an electrolyte. Several types of monopolar architecture geometry are known:

[0007] - a cylindrical geometry, with winding around a cylindrical axis such that disclosed in US patent application 2006 / 0121348;

[0008] - a prismatic geometry, with winding around a parallelepiped axis as disclosed in US Patents 7,348,098, US 7,338,733; and

[0009] - a stacking geometry as disclosed in US patent applications 2008 / 060189, US 2008 / 0057392, and US patent 7,335,448.

[0010] The electrolyte component may be in solid, liquid or gel form. In the latter form, the component may comprise a polymer or microporous composite separator soaked in organic or ionic liquid electrolyte(s) which allows the movement of the Lithium ion from the cathode to the anode for charging and vice versa for discharging, which generates the current. The electrolyte is generally a mixture of organic solvents, for example carbonates to which a lithium salt, typically LiPF6, is added.

[0011] The positive electrode or cathode is made of lithium cation insertion materials which are generally composite, such as for example lithium iron phosphate LiFePO4, lithium cobalt oxide LiCoO2, lithium manganese oxide, possibly substituted, LiMn2O4 or transition metal oxide, such as lamellar materials for example, a material based on LiNixMnyCozO2 with x+y+z = 1, such as for example LiNi0.33Mn0.33Co0.33O3, or a material based on nickel cobalt aluminum oxide type LiNixCoyAlzO2 with x+y+z = 1, such as LiNio.8Co0.15AI0. os02.

[0012] The negative electrode or anode is very often made of carbon, graphite or LqTisOn (titanate material), possibly perhaps based on silicon or a mixture of silicon with graphite or silicon oxide, or based on lithium, or based on tin and their alloys or a composite formed from silicon. This negative electrode, like the positive electrode, can also contain electronically conductive additives as well as polymer additives which give it mechanical properties and electrochemical performances appropriate to the lithium-ion battery application or to its implementation method.

[0013] The anode and the cathode made of lithium insertion material can be continuously deposited using a standard technique in the form of an active layer on a metal sheet or foil constituting a current collector.

[0014] The current collector connected to the positive electrode is generally made of aluminum.

[0015] The current collector connected to the negative electrode is generally made of copper, nickel, nickel-plated copper or aluminum.

[0016] More specifically, aluminum is used for the current collectors common to positive and negative electrodes of Li4Ti50i2 titanate. Copper is rather for the negative electrodes of graphite (Cgr), silicon (Si) or silicon composite (Si-C).

[0017] Traditionally, a Li-ion battery or accumulator uses a pair of materials at the anode and cathode allowing it to operate at a voltage level, typically between 1.5 and 4.3 Volts.

[0018] Depending on the type of application targeted, the aim is to produce either a thin and flexible lithium-ion accumulator or a rigid accumulator: the packaging is then either flexible or rigid and in the latter case constitutes a sort of case.

[0019] Rigid packaging (cases) is usually made from a metallic material, typically an aluminum alloy or stainless steel or a rigid polymer such as acrylonitrile butadiene styrene (ABS).

[0020] Flexible packaging, commonly referred to as "Pouch", is usually manufactured from a multi-layer composite material consisting of an aluminum foil covered by one or more polymer films laminated by bonding. In most of these flexible packagings, the polymer covering the aluminum is chosen from polyethylene (PE), propylene, polyamide (PA) or may be in the form of an adhesive layer consisting of polyester-polyurethane. The Showa Denko company markets this type of composite material for use as battery packaging under the references NADR-0N25 / AL40 / CPP40 or No. ADR-0N25 / AL40 / CPP80.

[0021] [Fig. 3] illustrates this type of flexible packaging 6 which is arranged to insulate and seal the electrochemical cell C while being crossed by a part of two strips or tongues 4, 5, commonly called in English "tab", forming the terminals or poles and which extend in the plane of the electrochemical cell. The tab 4, constituting the positive terminal, is in the form of a metal strip with a thickness generally of 0.2 to 0.4 mm, most often made of aluminum. The tab 5, constituting the negative terminal, is in the form of a metal strip of 0.2 to 0.4 mm in general, most often made of nickel material or copper or nickel-plated copper.

[0022] The main advantage of flexible packaging is its lightness. Li-ion batteries with the highest energy densities therefore have flexible packaging.

[0023] The total thickness of the accumulator with its flexible packaging is generally less than 16 mm, which is a function of the dimensions and the chemistry of the electrode materials, and this without altering the performance during operation of the accumulator. Furthermore, it is known to integrate a so-called reference electrode into a Li-ion accumulator and more generally, an electrochemical device, in particular for metal-ion batteries, in particular sodium-ion, lithium-ion batteries ion, potassium-ion, magnesium-ion; lithium-sulfur or lithium-air batteries; and supercapacitors, for example potassium hybrid supercapacitors.

[0024] It is recalled that a reference electrode is provided to maintain a stable and known electrochemical potential, under the conditions prevailing in an electrochemical measurement, advantageously making it possible to serve as a reference point for independently measuring the potential of the positive and negative electrodes in an electrochemical cell.

[0025] The reference electrodes proposed until now in electrochemical storage systems are based on lithium-based alloys (for example, LixSn, Lix Bi, LixAu, LixIn, LixSi, LixAl, etc.), respectively based on sodium, potassium, etc.; intercalation materials of LiM02 with M representing Co, Ni or Mn; or LiM'2O4 with M' representing Ni or Mn; or insertion materials such as LiM”PO4 with M” representing Fe, Co, Mn or Ni; or of the Li4Ti50i2 type.

[0026] US patent 9,379,418 discloses a Li-ion accumulator, in particular with flexible packaging with a reference electrode.

[0027] [Fig. 4] shows a conventional arrangement of a reference electrode 7 usually formed from a layer of the LiM”PO4-based electrode material at a current collector, for example made of aluminum or carbon-coated aluminum, within a battery 1 with flexible packaging 6. This reference electrode 7 is inserted into the thickness of the cell stack in contact with the electrolyte, between the cathode and the anode, and the collector of this reference electrode 7 passes tightly through the flexible packaging at an edge opposite that from which the collectors 4, 5 of the positive and negative electrodes respectively emerge.

[0028] In the field of supercapacitors, we can also cite US2011 / 0043968 which proposes, to evaluate the electrochemical characteristics of standard and hybrid lithium supercapacitor systems, to use a saturated calomel reference electrode (SCE).

[0029] The safety of metal-ion batteries must be considered both at the level of a single battery.

[0030] In particular, understanding the mechanisms of operation or degradation of the performance of lithium battery materials is now one of the essential axes of battery design and development.

[0031] Thus, in general, it is important that the operation of electrochemical devices does not fall outside their range of electrochemical and thermal stability so as not to cause damage, in particular due to the presence of a gas harmful to their operation, and in particular generated within the device.

[0032] It is thus known that a gas such as O2, or CO2 mixed with another oxidant such as O2 for example, can be capable of oxidizing LiFePO4.

[0033] It is also known that the presence of oxygen in a battery can initiate the chemical decomposition of battery components via exothermic reactions. This can lead to thermal runaway situations.

[0034] With regard to the thermal runaway phenomenon, reference is made to publication [1] and the protocol described in this publication. The so-called “self-heating” and “thermal runaway” temperatures are respectively denoted T1 and T2 in this publication.

[0035] The temperature Tl, typically 70°C, in [Fig.2] of the publication, is the temperature from which the accumulator heats up without an external source at a typical rate of 0.02°C / min in adiabatic conditions.

[0036] The temperature T2, typically 150°C, in [Fig.2] of the publication, is the temperature from which the accumulator heats up at a typical heating rate of 10°C / min under adiabatic conditions, which leads to the melting of the separator in the electrochemical beam of the accumulator, to a short circuit and therefore to the collapse of the voltage.

[0037] By "thermal runaway", we can thus understand here and within the framework of the invention, a ratio between the value of the derivative of the heating temperature and that of the time at least equal to 0.02°C per min.

[0038] It is therefore essential for an electrochemical device of the battery or supercapacitor type to be able to detect early on any undesirable presence of an oxidizing gas likely to react with the reduced form of the metal of the reference electrode, within at least one cell of the device, so as to prevent thermal runaway of the device.

[0039] In order to detect whether such an undesirable phenomenon occurs, it is necessary to have an effective means for monitoring the chemical evolution of the gaseous medium of an electrochemical system throughout its lifetime.

[0040] Various gas sensors have already been proposed to detect and, where appropriate, monitor the evolution of gases within a Li-ion accumulator.

[0041] We can thus cite CN117233328 A which describes a heterojunction sensor implanted in the flexible packaging of a Li-ion accumulator.

[0042] WO2022 / 252532 discloses a lithium-ion battery in which is implanted a fiber optic sensor.

[0043] WO2016 / 047232 describes a gas detection sensor in the form of a ribbon {Fe(pyrazine)(Ni(CN)4]}-based adhesive, which is attached to the outside of the battery to detect possible leaks.

[0044] CN116660779 A discloses a gas sensor consisting of electrodes made of two semiconductor materials, which are sensitive to electrolyte vapors.

[0045] However, all of the sensors disclosed are not suitable for detecting all oxidizing gases, or in particular oxygen, and / or cannot be implanted in all configurations (architectures, electrochemistry) of electrochemical devices.

[0046] There is therefore a need for reliable monitoring of the gaseous medium within an electrochemical device, such as a battery or supercapacitor, which overcomes all or part of the aforementioned drawbacks. Statement of the invention

[0047] Unexpectedly, the inventors have found that the electrochemical potential of an additional electrode of a specific nature, in addition to the negative and positive electrodes of an electrochemical device, and more particularly a lack of stability or even a drift of this potential, is an effective indicator of the presence of an undesirable oxidizing gas within the device, linked for example to abusive operating conditions and / or a malfunction of this electrochemical device.

[0048] More particularly, the inventors have discovered that it is possible to use an additional electrode based on at least one conductive, ionic, electroactive and oxidizable element or material, in particular with an adjusted redox potential, as a means of detecting the presence of an undesirable oxidizing gas in an electrochemical device.

[0049] Thus, the invention relates, according to a first of its aspects, to the use of an additional electrode based on at least one ionic, electroactive and oxidizable conductive element or material in an electrochemical device comprising at least one electrochemical cell comprising a positive electrode, a negative electrode and an electrolyte, as a means of detecting the presence or absence of an oxidizing gas in said electrochemical device, said additional electrode having a redox potential lower than that of said oxidizing gas.

[0050] By "gas" is meant indifferently here and within the framework of the present invention, a single oxidizing gas or an oxidizing mixture of at least two gases.

[0051] By "oxidizing gas" is meant here and within the framework of the present invention, a gas capable of interacting with at least one component of the device and in particular with the reduced form of the metal of the additional electrode of the electrochemical device.

[0052] According to one embodiment, the oxidizing gas is chosen from oxygen, CO2 and their mixtures. In particular, said gas contains at least oxygen.

[0053] It is also understood that the detection of an oxidizing gas also means a fortiori the detection of a presence of gas, in an environment which is not supposed to contain it, and therefore representative of abnormal internal conditions.

[0054] By "additional electrode" is meant here and within the scope of the invention, a component based on at least one conductive, ionic, electroactive and oxidizable element or material intended to be implanted within a packaging of an electrochemical device, and which is distinct from the negative (anode) and positive (cathode) electrode(s), also called working electrodes or counter-electrode, of the device.

[0055] In particular, said additional electrode has a redox potential lower than that of oxygen.

[0056] According to another of its aspects, the present invention thus relates to a method for detecting the presence or absence of an oxidizing gas in an electrochemical device comprising at least one electrochemical cell comprising a positive electrode, a negative electrode and an electrolyte, comprising at least the steps consisting of:

[0057] i / having at least one additional electrode, within said device, said additional electrode being based on at least one ionic, electroactive, oxidizable element or material with a redox potential lower than that of said oxidizing gas;

[0058] ii / arranging said additional electrode at least partly in an area within said device suitable for gas concentration, under operating conditions of the device; and

[0059] iii / monitoring the evolution of the potential of the additional electrode in relation to its nominal value, so as to detect the presence or absence of said oxidizing gas in said device.

[0060] According to a particular embodiment, said oxidizing gas is produced within the device.

[0061] According to another particular embodiment, said oxidizing gas is a gas which has penetrated into the device.

[0062] Thus, monitoring the variation in the potential of the additional electrode during operation of the electrochemical device advantageously makes it possible to detect, if present, the undesirable presence of an oxidizing gas and thus allows improved safety in the use of the electrochemical device in question.

[0063] This detection mode can thus make it possible to characterize degrading conditions in progress on an electrochemical device, for example linked to the environment and / or to electrical faults, and an electrical check of the electrochemical device can be provided as a safety corrective measure.

[0064] Step ii / is preferably carried out by arranging the additional electrode in an area located on top of the electrochemical device, more preferably in an area above the major part of the electrochemical cell(s).

[0065] According to a first variant embodiment, step iii / is carried out by comparing the potential of the additional electrode with that of the positive and / or negative electrode of the electrochemical device.

[0066] According to a second variant embodiment, step iii / is carried out by comparing the potential of the additional electrode with that of another additional electrode, not arranged in an area conducive to the accumulation of gas.

[0067] Step iii / may advantageously consist of comparing the variation in the potential of the additional electrode with respect to a threshold value, and if the variation is greater than said threshold value, then considering the presence of said oxidizing gas, such as for example O2 mixed or not with CO2.

[0068] In particular, the oxidizing gas to be detected is chosen from oxygen, CO2 and their mixtures and in particular contains at least oxygen.

[0069] In particular, the additional electrode has a redox potential lower than that of oxygen.

[0070] The detection method according to the invention can take place continuously during the first life of the electrochemical device and / or serve as a diagnosis for a possible second life use of the device.

[0071] The invention also relates, in another of its aspects, to a method for controlling an electrochemical device for which a detection method as described above has been implemented, the method comprising, in the event of the threshold value being exceeded, at least one step consisting of generating an electrical action on the electrochemical cell. This electrical action may consist of a variation or interruption of the electrical charge, in particular for rebalancing purposes.

[0072] The control method may advantageously comprise a step of evacuating the gas release from the electrochemical device.

[0073] Once the gas release has been evacuated, the method may advantageously comprise a step of inserting metal ions into the additional electrode. This insertion may consist of an electrical recharge, at least partial, of the additional electrode, in particular for a device of the metal-ion battery or hybrid supercapacitor type.

[0074] The invention finally relates to a system comprising:

[0075] - an electrochemical device comprising at least one electrochemical cell comprising a positive electrode, a negative electrode and an electrolyte;

[0076] - an additional electrode based on at least one ionic element or material, electro-active, oxidizable and with a redox potential lower than that of an oxidizing gas in particular chosen from oxygen, CO2 and their mixtures, said electrode being arranged at least partly in an area within said device conducive to the concentration of gas, under operating conditions of the device and

[0077] - means for monitoring the evolution of the potential of the additional electrode.

[0078] Advantageously, the additional electrode is a reference electrode, that is to say an electrode intended to serve as a reference potential in the electrochemical device. In the absence of drift or variation in the potential of the reference electrode, the latter plays its primary function of indicating a reference potential and therefore of providing information on the internal state of the electrochemical device in order to optimize its control, its charging and / or its discharging.

[0079] According to this embodiment, its redox potential is lower than that of oxygen.

[0080] According to a preferred application, the electrochemical device comprises at least one metal-ion battery or accumulator.

[0081] Preferably:

[0082] - the negative electrode(s) material is chosen from the group comprising the graphite, lithium, titanate oxide Li4Ti50i2; and

[0083] - the positive electrode(s) material is chosen from the group of compounds of intercalation / insertion of LiM02 type with M representing one or more identical or different metal salts chosen from Al, Co, Ni and Mn; of LiM'2O4 type with M' representing one or more identical or different metal salts chosen from Ni and Mn; or of LiM”PO4 type with M” representing one or more identical or different metal salts chosen from Fe, Co, Mn or Ni.

[0084] In this preferred application, the tracking means can be integrated into a battery management system (BMS), to which the additional electrode is electrically connected.

[0085] According to an advantageous embodiment, in the event of a variation in the potential of the additional electrode above a predetermined threshold value, the BMS is configured to act electrically on the device. This may be an action of interruption or reduction of electrical charge.

[0086] According to a variant of the invention, the additional electrode is a LiFePO4 electrode which has or has not undergone partial delithiation (deintercalation of lithium ions). In particular, it is a reference electrode based on Lii xFePO4, with 0.30 < x < 0.70, in particular 0.40 < x < 0.60.

[0087] More generally, the additional electrode can be based on a partially (de)lithiated material such as LCO, NMC, LMO, Graphite, etc. which is sensitive to oxygen and other oxidizing gases such as CO2. Reference may be made to publication [2].

[0088] Other characteristics, variants and advantages of the invention will become more apparent upon reading the description, examples and figures which follow, given for illustrative and non-limiting purposes of the invention. Brief description of the drawings

[0089] [Fig.l] [Fig.l] is an exploded perspective schematic view showing the various elements of a lithium-ion accumulator.

[0090] [Fig.2] [Fig.2] is a front view showing a prismatic format lithium-ion accumulator with its flexible packaging according to the state of the art.

[0091] [Fig.3] [Fig.3] is a perspective view of a prismatic format lithium-ion accumulator with its flexible packaging according to the state of the art.

[0092] [Fig.4] [Fig.4] is a perspective view of a prismatic format lithium-ion accumulator with its flexible packaging according to the state of the art which integrates a reference electrode.

[0093] [Fig.5] [Fig.5] represents the photograph of a soft-packaged Li-ion battery as according to the architecture of [Fig.4], instrumented with glassy carbon windows and a stainless steel support / frame for acquisition on a SAXS / WAXS line.

[0094] [Fig.6] [Fig.6] represents the electrochemical charge and discharge curves obtained during 2 cycles with different upper cut-off limits for two identical cells A, B with LNO and GrSi electrode electrochemistry with partially delithiated LFP reference electrodes in EC / 1.3M LiPF6, 10 wt% FEC electrolyte tested respectively with a different arrangement.

[0095] [Fig.7] [Fig.7] represents the evolution of the WAXS line pattern at the position of the reference electrode during an overload for each of the two cells A and B.

[0096] [Fig.8] [Fig.8] represents at the top the voltage profiles of cell A during its electrochemical cycling with cut-off voltages of 4.2V and 5.0V vs Li / Li+ for the 1st and 2nd cycles respectively, and at the bottom the corresponding gas evolution curves obtained by OEMS method.

[0097] Figures 1 to 4 relate to different examples of Li-ion accumulators, flexible packaging according to the state of the art. These figures 1 to 4 have already been commented on in the preamble and are therefore not commented on below.

[0098] Throughout the present application, the terms "lower", "upper", "bottom", "top", "below" and "above" are to be understood with reference to an electrochemical device according to the invention as it is positioned under operating conditions.

[0099] The inventors tested two identical Li-ion accumulators, with a single electrochemical cell, with flexible packaging whose architecture is the same as that shown in [Fig.4].

[0100] The flexible packaging is based on an aluminum laminated film, Showa Denko Packaging, ref Laminated Al. Foil Type No. ADR-ON25 / AL40 / CPP40.

[0101] Thus, in this configuration, the reference electrode 7 has been inserted between the cathode and the anode, being electrically insulated by a separator layer of each side, and it is arranged on the side edge opposite that from which the current collectors 4, 5 emerge.

[0102] Each of the two cells was prepared according to the method described below.

[0103] In a first cell called cell A, the reference electrode 5 is, during electrochemical operation, arranged in the upper position in cell A which is oriented vertically. In this configuration, the gases, if generated by the cell, will first be directed towards the top of the flexible packaging, then evacuated by a flow of carrier gas. Cell A is tested electrochemically with simultaneous acquisition of data on a SAXS line (acronym for "Small-Angle-X-ray-Scattering") and WAXS line (acronym for "Wide-Angle-X-ray-Scattering").

[0104] [Fig.5] shows this test configuration. In the second cell, called cell B, the reference electrode 7 is, during electrochemical operation, in horizontal orientation, i.e. the three electrodes 4, 5, 7 are at the same altitude. Consequently, the gases, if formed, during the electrochemical test will be uniformly distributed inside the cell.

[0105] This B cell was tested electrochemically in the laboratory without X-ray data acquisition. Materials and methods

[0106] - Reference electrode 7 is a partially delithiated LiFePO4 (LFP) electrode of approximately 0.2 x 0.2 cm2. It was partially electrochemically predelithiated at a 1 / 1 LFP / FP phase fraction to ensure a stable electrochemical potential of 3.42 V versus Li / Li+.

[0107] - A triple filter quadrupole mass spectrometer marketed under the A Hiden HPR20 S1000 with pulsed ion counting electron multiplier detector was used for the measurements. Each of the cells A and B was purged with Argon for 3 hours to stabilize the base gas signals before starting the electrochemical test. The following m / z values ​​were measured in multiple ion detection mode: 44 (CO2), 2 (H2), 28 (CO + C2H4 mainly with a minor contribution from (CO2)), 29 (CO + C2H4 mainly), 32 (O2), 15 (CH4), 41 (C3H6). The volume of the electrochemical cell A or B is 10 ml and the response time for OEMS analysis is 5 minutes.

[0108] - SAXS / WAXS lines: A 65 x 100 micron beam at 18 keV was used (1 = 0.6888011 Å). During acquisition, cell A was moved to scan the beam across the entire surface of the positive and negative electrodes, producing 31x31 pixel maps with a pixel size of 1 mm in approximately 5 minutes.

[0109] Each pixel contained a WAXS and SAXS pattern. To achieve this temporal resolution, "on-the-fly scans" were performed by continuously moving the pocket in the x direction from 0 to 31 mm while keeping the shutter open. The detector images were averaged over a 1 mm displacement of the A-cell.

[0110] Therefore, the detector image was an average in the x direction of 1 mm of the sample. Example 1 [YES] Preparation of two cells _ A, B and characterization of their implementation parameters

[0112] The two cells A, B are made with a positive electrode in LiNiO2, and negative in commercially available GrSi, deposited as usual by coating on Al, Cu collector strips. The capacity charges of the positive and negative electrodes are respectively 3 mAh.cm 2 and 3.3 mAh.cm 2

[0113] The separator consists of two layers marketed under the name DreamWeaver Gold™, which is a non-woven sheet made of Kevlar-type fibers.

[0114] The electrolyte is 1.3 M LiPF6 in ethylene carbonate (EC) and 10 wt% fluoroethylene carbonate (FEC). The separator was chosen to ensure good wettability with the electrolyte.

[0115] Cells A and B were assembled in a dry room with a dew point of -40°C and all components were dried before assembly at 105°C under vacuum for 24h.

[0116] The surface area of ​​the positive electrode in LiNiO2 is equal to 2.3 x 2.3 cm2 and 2.7 x 2.7 cm2 for the negative electrode in GrSi, while that of the separator was greater, equal to 4.0 x 4.0 cm2, to avoid short circuits.

[0117] 1 / 32" diameter PEEK tubes were sealed in each A, B cell using a heat-sealing polymer and served as the gas inlet and outlet for each A, B cell.

[0118] Tabs forming the outputs, respectively positive in Al and negative in Cu, were also sealed in each cell A, B using a heat-sealing polymer.

[0119] After assembly, each cell A, B was pressed between two glassy carbon windows, with a surface area of ​​4 x 4 cm2 and a thickness of 0.5 mm using perforated plates and stainless steel clips. The visible surface, accessible for possible observations by the SAXS / WAXS lines, was 2.5 x 2.5 cm2.

[0120] The electrochemical cycle of each cell A, B was carried out using the potentiostat marketed under the name SP-300 by the company BioLogic in galvanostatic and potentiostatic modes by controlling the total voltage of the cell, i.e. i.e. between the negative electrode (anode) and the positive electrode (cathode), while measuring the potentials of these positive and negative electrodes relative to the reference electrode.

[0121] The formation cycle was performed at a value of C / 13 with cut-off voltages of 4.2 V and 2.5 V with respect to Li / Li+ with potentiostatic hold at the end of the charge. During this formation cycle, the voltage control limits were applied between the positive and negative electrodes. The potentials of the positive and negative electrodes were checked by the reference electrode.

[0122] The end of hold conditions were obtained by limiting the current to 0.24 mA or the step time to 2 h.

[0123] The overcharge cycle was performed at C / 9 with cut-off voltages of 5.0 -2.5 V with a 3-hour hold at 5 V at the end of the charge. It should be noted that the hold was interrupted after 30 minutes for a short OCV (Open Circuit Voltage) duration of 7 minutes.

[0124] The temperature during the tests was 26°C. Example 2

[0125] Electrochemical test of cells A and B of example 1 and characterization of O2 release with cell A

[0126] Each cell A, B was mounted on the SAXS / WAXS beamline.

[0127] An online gas analysis method by mass spectroscopy was applied to analyze the gases released during the electrochemical test of the cell. For this purpose, a gas analysis line containing mainly 1 / 8" metal tubes was constructed around the cell.

[0128] Argon marketed under the name BIP®, ultra pure (> 99.9999%) was used as the carrier gas.

[0129] A gas purification column was installed before the electrochemical cell A or B, in order to remove any possible residual impurities from the tubes.

[0130] A digital mass flow controller was used to provide a constant flow of argon of 2 mL.min 1 to the cell.

[0131] The gas analysis line was equipped with a vacuum pump and a bypass to be able to clean / purge the tubing before passing the gas into the cell.

[0132] A 1 / 32" flexible PEEK tube sealed into the cell on both sides ([Fig.5]) allowed uninterrupted gas flow through either cell A or B. Results

[0133] [Fig.6] compares the electrochemical results obtained for the two cells A and B. The curves on the left of this [Fig.6] are relative to cell A while those on the right are relative to cell B.

[0134] It is found that the voltage profiles are very similar for both complete cells A and B, as tested. Therefore, there was no impact of a beam line on the electrochemical performance of either cell A, B.

[0135] The profiles of the positive electrodes show a specific characteristic for cell A, in particular at the end of the second charge at 5V, there is a potential drop from 5.02 V vs Li / Li+ at the beginning of a stage to 4.6 V at the end of the stage. In addition, there is a potential drop at the beginning of the second discharge.

[0136] For the negative electrode, a significant drop in potential is also observed at the end of the second charge from 0.02V to -0.4V vs Li / Li+ for cell A. These characteristics are negligibly low for the laboratory test (cell B). The potential drops for the positive and negative electrodes of cell B during the 5V hold are approximately 0.01 and 0.04V, respectively.

[0137] It is therefore evident that the reference electrode 7 did not function correctly for the vertically oriented cell A, where it was in the upper position, because its potential drop during the maintenance of 5 V is abnormal.

[0138] The LFP reference electrode was spontaneously delithiated during the test, which explains the deviations in the measured potentials. The fact of delithiation was confirmed by two separate methods, namely operando analysis by the WAXS line during the experiment and a post-mortem electrochemical analysis of the reference electrodes.

[0139] [Fig.7] shows the evolution of the pattern resulting from the WAXS analysis at the position of the reference electrode 7 of an overload (rise): the LFP peak located at 2.10 Å disappears while the FP peak gains in intensity at the end of the overload for cell A.

[0140] We therefore observe almost total delithiation of the LFP reference electrode.

[0141] [Fig.8] establishes that this almost complete spontaneous delithiation of the LFP is due to its oxidation by at least the oxygen released at high voltage by the cell components. The voltage profiles are superimposed on the gas evolution profiles showing that the evolution of the oxidizing gas is consistent with the potential drops measured for cell A. List of cited documents

[0142] [1]: Xuning Feng, et al. « Thermal runaway mechanism of lithium - ion battery for electric vehicles: A review”, Energy Storage Materials, Volume 10, January 2018, Pages 246-267.

[0143] [2]: 'Air sensitivity of electrode materials in Li / Na ion batteries': Issues and strategies (DOI: 10.1002 / inf2.12305.

Claims

Claims

1. Use of an additional electrode based on at least one ionic, electroactive and oxidizable conductive element or material in an electrochemical device comprising at least one electrochemical cell comprising a positive electrode, a negative electrode and an electrolyte, as a means for detecting the presence or absence of an oxidizing gas in said electrochemical device, said additional electrode having a redox potential lower than that of said oxidizing gas.

2. Use according to the preceding claim in which said oxidizing gas is chosen from oxygen, CO2 and their mixtures and in particular contains at least oxygen.

3. Use according to claim 1 or 2 wherein said additional electrode has a redox potential lower than that of oxygen.

4. Method for detecting the presence or absence of an oxidizing gas in an electrochemical device comprising at least one electrochemical cell comprising a positive electrode, a negative electrode and an electrolyte, comprising at least the steps of: i / providing at least one additional electrode, within said device, said additional electrode being based on at least one ionic, electroactive, oxidizable element or material with a redox potential lower than that of said oxidizing gas; ii / arranging said additional electrode at least partly in an area within said device conducive to the concentration of gas, under operating conditions of the device; and i / monitoring the evolution of the potential of the additional electrode relative to its nominal value, so as to detect the presence or absence of said oxidizing gas in said device.

5. A method according to claim 4, wherein step ii / is carried out by arranging the additional electrode in an area located on top of the electrochemical device, more preferably in an area above the major part of the electrochemical cell(s).

6. Method according to claim 4 or 5, step iii / being carried out by comparing the potential of the additional electrode with that of the positive and / or negative electrode of the electrochemical device.

7. Method according to claim 4 or 5, step iii / being carried out by comparing the potential of the additional electrode with that of another additional electrode, not arranged in an area conducive to the accumulation of gas.

8. Method according to one of claims 4 to 7, step iii / consisting of comparing the variation in the potential of the additional electrode with respect to a threshold value, and if the variation is greater than said threshold value then considering the presence of said oxidizing gas.

9. Method according to one of claims 4 to 8, said oxidizing gas being chosen from oxygen, CO2 and their mixtures and in particular containing at least oxygen.

10. Method according to one of claims 4 to 9, said additional electrode having a redox potential lower than that of oxygen.

11. Method according to one of claims 4 to 10, said additional electrode being a LiFePO4 electrode having undergone or not partial delithiation, in particular, a reference electrode based on Lii xFePO4, with 0.30 < x < 0.70, in particular 0.40 < x < 0.

60.

12. Method for controlling an electrochemical device for which a detection method according to one of claims 4 to 11 has been implemented, the method comprising, in the event of the threshold value being exceeded, at least one step consisting of generating an electrical action on the electrochemical cell.

13. Control method according to claim 12, the electrical action consisting of a variation or interruption of the electrical charge, in particular for rebalancing purposes.

14. A control method according to claim 12 or 13, comprising a step of evacuating the gaseous release from the electrochemical device.

15. A control method according to claim 14, comprising, once the gas release has been evacuated, a step of inserting metal ions into the additional electrode.

16. System comprising: - an electrochemical device comprising at least one electrochemical cell comprising a positive electrode, a negative electrode and an electrolyte;

17. - an additional electrode based on at least one ionic, electroactive, oxidizable conductive element or material with a redox potential lower than that of an oxidizing gas, in particular chosen from oxygen, CO2 and their mixtures, said electrode being arranged at least partly in an area within said device conducive to the concentration of gas, under operating conditions of the device; and - means of monitoring the evolution of the potential of the additional electrode. System according to claim 16, the additional electrode being a reference electrode and in particular having a redox potential lower than that of oxygen.

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