System and method for the non-destructive testing of the aging of a battery in operation

Abstract

The present invention relates to an in-operando and non-destructive testing system (10) for testing the aging of at least one electrochemical element of a battery, the in-operando and non-destructive testing system (10) comprising: - a cavity (30); - a source (24) configured to emit L-band electromagnetic waves toward the cavity (30), the cavity (30) comprising a cylindrical resonator (38) with a circular base and having at least one longitudinal cut-out (46, 48); - a detector (28) capable of detecting the waves originating from the cavity (30); and - a processor (34) capable of analyzing the waves detected by the detector (28) in order to obtain at least one item of information relating to the aging of the at least one electrochemical element.

Description

[0001] System and method for non-destructive testing of the aging of an accumulator in operation

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The present invention relates to an in-operando, non-destructive system for monitoring the aging of a battery. The present invention also relates to an associated monitoring method.

[0004] BACKGROUND OF THE INVENTION

[0005] Typically, a battery comprises one or more current storage cells, also called electrochemical cells or elements. A battery is an electrochemical storage device in which chemical energy is converted into electrical energy. The chemical energy comes from electrochemically active compounds deposited on at least one side of electrodes arranged within the battery. The electrical energy is produced by electrochemical reactions during the battery's discharge. The electrodes, arranged in a container, are electrically connected to current output terminals that ensure electrical continuity between the electrodes and the electrical load to which the battery is connected.

[0006] To increase the delivered capacity, several sealed accumulators can be connected together to form a battery. A battery can thus be divided into modules, each module consisting of one or more accumulators connected in series and / or parallel. For example, a battery can have one or more parallel branches of accumulators connected in series and / or one or more parallel branches of modules connected in series.

[0007] A charging circuit is usually provided to which the battery can be connected to recharge the cells.

[0008] In the remainder of this application, we will use the more general term battery to describe the electrochemical system.

[0009] Furthermore, an electronic management system, including measurement sensors and an electronic control circuit of varying complexity depending on the application, can be connected to the battery. Such a system allows, in particular, the organization and control of the battery's charging and discharging, balancing the charge and discharge of the battery's individual cells relative to one another.

[0010] It is therefore desirable to be able to monitor the cycling (i.e., the sequence of charges and discharges) of a battery in real time. This allows access to all types of information, including the state of charge and battery aging, such as the nucleation of lithium dendrites.

[0011] For this purpose, it is known to use electronic paramagnetic resonance to monitor the evolution of a battery using conventional electronic paramagnetic resonance systems operating between 9.4 GHz and 10 GHz (frequency band often called X band), allows to follow in real time and under operating conditions the electrochemical evolution (redox processes and degradation processes) involved in a battery.

[0012] Conventionally used X-band EPR spectrometers can only analyze samples of a small size, which prevents the use of a commercial battery due to its dimensions.

[0013] To remedy such a problem, the technique is either implemented on so-called model batteries not intended for commercial use or implemented on batteries whose packaging has been destroyed, rendering them unusable.

[0014] In this sense, the known technique is destructive to a commercial battery since it requires opening the battery.

[0015] SUMMARY OF THE INVENTION

[0016] There is therefore a need for a non-destructive aging control system for a battery that can be implemented inoperable with any type of battery, including a lithium-ion battery or any solid used commercially, regardless of its shape (pouch, prismatic or cylindrical).

[0017] To this end, the description describes an inoperable and non-destructive aging control system for at least one electrochemical element of a battery, the inoperable and non-destructive control system comprising:

[0018] - a cavity,

[0019] - a source configured to emit L-band electromagnetic waves towards the cavity, the cavity comprising a cylindrical resonator with a circular base having at least one longitudinal cutout,

[0020] - a detector specifically designed to detect waves emanating from the cavity, and

[0021] - a computer capable of analyzing the waves detected by the detector to obtain at least one piece of information relating to the aging of at least one electrochemical element.

[0022] The testing system is non-destructive in the sense that the physicochemical properties of the electrode materials in the battery are not altered during or after the analysis. In other words, after testing, a user can take back the battery and use it as is.

[0023] The control system is an inoperative control system. Such control refers to the fact that the control can be carried out while the accumulator is operating, that is to say in the presence of reaction conditions with the formation of products of the electrochemical reaction (lithia graphite, dendrite or plating).

[0024] Of course, this does not preclude the control system from being used in simple conditions, including with the accumulator off, to perform a post-mortem check.

[0025] In specific embodiments, the control system has one or more of the following characteristics, taken individually or in all technically possible combinations:

[0026] - the source is configured to emit electromagnetic waves with a frequency between 0.99 GHz and 1.10 GHz.

[0027] - the resonator defines an internal volume sized to accommodate a battery having a pouch shape, a prismatic shape or a cylindrical shape.

[0028] - the circular base of the cylindrical shape of the resonator has a radius, the radius being greater than or equal to 1 centimeter, preferably greater than or equal to 3 centimeters, advantageously greater than or equal to 5 centimeters.

[0029] - the cavity is equipped with a sample holder designed to hold the accumulator in position.

[0030] - the sample holder has two retaining elements designed to cooperate together to maintain the accumulator in a central position within the internal volume.

[0031] - the retaining elements are held under pressure by fasteners.

[0032] - the control system also includes a unit for controlling the temperature of the internal volume of the resonator.

[0033] - at least one piece of information relating to the aging of at least one electrochemical element is chosen from a list consisting of the state of charge of the at least one electrochemical element, a parameter related to the aging of the at least one electrochemical element, the presence or absence of an abnormal structure and the location of the abnormal structure, the abnormal structure preferably being a metallic aggregate or a dendrite. The description also concerns a method for inoperative and non-destructively monitoring the aging of at least one electrochemical element of a battery, the monitoring method comprising the following steps:

[0034] - emission of L-band electromagnetic waves towards a cavity, the cavity comprising a cylindrical resonator with a circular base having at least one longitudinal cutout,

[0035] - detection of waves emanating from the cavity, and

[0036] - analyze detected waves to obtain at least one piece of information relating to the aging of at least one electrochemical element.

[0037] In this description, the expression "specific to" means interchangeably "suited for", "adapted to" or "configured for".

[0038] BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings, in which:

[0040] - Figure 1 is a schematic representation of a non-destructive battery aging control system,

[0041] - Figure 2 is a view of an example of a battery pack in the form of a pouch,

[0042] - Figure 3 is an exploded perspective view of the battery in Figure 2,

[0043] - Figure 4 is an exploded perspective view of a sample holder used in the control system of Figure 1,

[0044] - Figure 5 is a representation of the positioning of a battery in pouch form within the sample holder shown in Figure 4.

[0045] - Figure 6 is a representation of the positioning of the sample holder with a battery in a part of the control system of Figure 1,

[0046] - Figures 7 to 10 are figures showing experimental results obtained by the Applicant.

[0047] DETAILED DESCRIPTION OF PREFERRED IMPLEMENTATION METHODS

[0048] A control system 10 is schematically represented in Figure 1.

[0049] The control system 10 is designed to control an accumulator 12, which here is a battery 12.

[0050] In this particular case, but not limited to, the 12 battery is in pouch form. This format is often referred to by the corresponding English term "pouch" and is particularly attractive for its compact size, light weight, and ease of production in various shapes and sizes.

[0051] As is known in itself, a 12 battery is generally an arrangement of a plurality of electrochemical elements, but for the sake of simplicity, a case with a single electrochemical element is described below, knowing that the transposition to other arrangements is immediate.

[0052] Battery 12 includes an electrochemical element and an electrochemical element management system.

[0053] As explained previously, an electrochemical element is an electricity-producing device in which chemical energy is converted into electrical energy.

[0054] The electrochemical element therefore delivers a current and a voltage between two terminals.

[0055] The chemistry of the electrochemical element can be of any nature compatible with the implementation of the characterization technique used by the control system 10.

[0056] Preferably, however, battery 12 is a lithium-ion battery or an all-solid-state battery.

[0057] The management system is a system specifically designed to manage the electrochemical element.

[0058] An example of a 12 battery in the form of a standard aluminized pouch can be seen in figures 2 and 3.

[0059] Battery 12 has a rectangular wall 14 encompassing the elements of Figure 3, namely an anode 16, a cathode 18 and a separator 20.

[0060] Wall 14 forms a pocket 21 visible in figure 2.

[0061] Wall 14 here has dimensions on the order of several centimeters.

[0062] A respective contact 22 emerges from the pocket 21 for the anode 16 and the cathode 18 to allow control of the aging of the battery 12.

[0063] The wall 14 is made of a deformable material, Figure 2 showing a pocket 21 in which the electrochemical element is placed.

[0064] The material of wall 14 includes metallic elements, typically aluminium.

[0065] For example, wall 14 is an aluminum film, preferably laminated.

[0066] The control system 10 is designed to control all forms of aging during the cycling of the electrochemical element contained within the wall 14.

[0067] Aging control here encompasses many different aspects, from controlling redox reactions in battery 12 to monitoring dendrite formation in the electrochemical element. Several examples will become apparent upon reading this description. Furthermore, control system 10 is a non-destructive testing system since it can operate on a battery without opening it (i.e., without removing its packaging).

[0068] For this purpose, the control system 10 exploits electron paramagnetic resonance (EPR).

[0069] EPR is a non-destructive spectroscopic technique that detects paramagnetic (and also magnetic) species present in a given sample. EPR provides access to the electronic structure and allows, in particular, the observation of microwave absorption by paramagnetic or conductive systems when they are subjected to a strong magnetic field.

[0070] More specifically, the EPR technique is a volumetric characterization technique that allows, in a material, the obtaining of information concerning the nature of species comprising unpaired or single electrons, as well as information on their concentrations, their reactivity, their environment, their dynamics and the magnetic interactions between these species and with other magnetic species.

[0071] The principle of the EPR technique is based on the Zeeman effect: when subjected to an external magnetic field H, the energy levels of a spin S separate into (2S + 1) electronic subspaces (lifting of degeneracy), each assigned a quantum number m s (m = -S, -S+1 , - S+2, ..., S). This separation of levels is greater the more intense H is.

[0072] Thus, for the case of a single unpaired electron (therefore for which S = 1 / 2), the presence of the external magnetic field gives rise to (2S + 1) = 2 electronic subspaces, corresponding to m s = -1 / 2 and m s = +1 / 2. Magnetic energy E M associated with each of these states is given by the following formula:

[0073] E M = m s * g * |i B * H

[0074] Or :

[0075] • g is the factor of Landé,

[0076] • |i B is the Bohr magneton, and

[0077] • H is the amplitude of the magnetic field.

[0078] Under the influence of a second magnetic field (microwave or microwave field) perpendicular to the first and of much lower amplitude, having a frequency v, a photon of energy hv can be absorbed (or emitted) if the energy separation between the two levels concerned, that is, g * |i B* H, is equal to hv. It is at this particular value of H that a resonance phenomenon occurs. In the example of Figure 1, the control system 10 comprises a source 24, a magnetic field generator 26, a detector 28, a cavity 30, a sample holder 32 (not shown in Figure 1 for clarity) and a computer 34.

[0079] Source 24 is suitable for exciting cavity 30 with L-band electromagnetic waves.

[0080] The L band includes frequencies between 0.9 GHz and 2 GHz.

[0081] Preferably, the wave emitted by source 24 is between 0.99 GHz and 1.10 GHz

[0082] Source 24 is therefore a microwave source.

[0083] EPR measurements or images are acquired in continuous or pulsed mode. For the purposes of this document, and without limitation, only continuous mode is considered, so source 24 is considered here as a continuous source.

[0084] The magnetic field generator 26 is suitable for applying a static magnetic field in the cavity 30.

[0085] The magnetic field generator 26 is, for example, a set of current-powered coils, the current control allowing control of the amplitude of the static field in the cavity 30.

[0086] The magnetic field generator 26 is suitable for applying a static magnetic field in the cavity 30.

[0087] In the case of Figure 1, the magnetic field generator 26 is a set of current-fed coils (two in this figure), with current control allowing control of the amplitude of the static field in the cavity 30.

[0088] Detector 28 is specifically designed to detect waves originating from cavity 30.

[0089] The waves coming from cavity 30 contain data relating to the electrochemical element.

[0090] In this case, this data makes it possible to obtain a spectrum (corresponding to a variation in field of a physical quantity) of the electrochemical element or an image of the electrochemical element (corresponding to a spatial variation of a physical quantity).

[0091] Detector 28 is thus suitable for detecting data relating to the electrochemical element.

[0092] According to the example in Figure 1, detector 28 is a detection diode.

[0093] The cavity 30 includes an enclosure 36 and a resonator 38.

[0094] The enclosure 36 surrounds the resonator 38 and thus acts as a shield.

[0095] Enclosure 36 has a cylindrical shape.

[0096] The base of this cylinder is a disk with a radius denoted R hereafter. The resonator 38 is designed to house the battery 12 containing the electrochemical element to be studied.

[0097] This means that resonator 38 delimits an internal volume configured to accommodate pouch 21.

[0098] Resonator 38 has the shape of a cylinder with a circular base.

[0099] The generatrix of the cylinder is in a longitudinal direction corresponding to the axis marked X on figure 1.

[0100] The other directions are noted as first transverse direction Y and second transverse direction Y.

[0101] The circular base corresponds to a disk with a radius denoted r in the following.

[0102] The resonator 38 has a length z (dimension along the longitudinal direction X).

[0103] The resonator 38 has an external wall 40 positioned opposite the interior of the enclosure 36 and an internal wall 42 delimiting an internal volume 44 in which the battery 12 is intended to be received.

[0104] In Figure 2, the X, Y and Z axes are shown to illustrate how battery 12 is inserted into the internal volume 44.

[0105] The length of wall 14 of battery 12 is along the longitudinal direction X while the width of wall 14 is along the second transverse direction Z.

[0106] The distance between the inner wall 42 of the resonator 38 and the outer wall 40 of the resonator 38 is the same at every point.

[0107] This inter-wall distance corresponds to the thickness of resonator 38.

[0108] The thickness of resonator 38 is noted as w.

[0109] According to the example described, the resonator 38 has two longitudinal cutouts 46 and 48.

[0110] Each cutout 46 and 48 has the same shape and extends from one end of the resonator 38 to the other

[0111] Each cutout 46 and 48 has a width t.

[0112] The two cutouts 46 and 48 are placed symmetrically with respect to the center of the resonator 38.

[0113] Thus, resonator 38 has the shape of two arcs of circles separated by an interval.

[0114] Because of this arrangement, such a resonator 38 is often called a "loop-gap," literally meaning loop-interval, the term "loop" referring to the arcs of circles and the term "gap" relating to the space formed by each cutout. Given that the internal volume of the resonator 38 is sized to accommodate a pouch 21 (corresponding to a commonly used industrial drum kit), the length of the resonator 38 is at least 70 mm and the radius R is greater than or equal to 1 centimeter, preferably greater than or equal to 3 cm, advantageously greater than or equal to 5 cm.

[0115] In operation, as seen in the enlarged view of Figure 1, the electric field E is confined to the capacitive air gap (at the level of each cutout) while the magnetic field B is confined inside the inductive loop (between the resonator 38 and the enclosure 36).

[0116] The sample holder 32 comprises two retaining elements 50 and 52 and two fasteners 54 and 56.

[0117] The two retaining elements 50 and 52 cooperate together to hold battery 12 in a central position.

[0118] In addition, this cooperation allows for precise control of the pressure applied to the battery 12 during electrochemical cycling to maintain good contact between the different materials present inside the pouch 21 forming the battery 12.

[0119] According to the example described, the two retaining elements 50 and 52 have the same shape.

[0120] Each retaining element 50 and 52 comprises a plate 58 with a central projection 60 and two orifices 62 and 64.

[0121] Plate 58 has a rectangular shape.

[0122] Each central projection 60 also has a rectangular shape.

[0123] When battery 12 is positioned, it is held in the centre by compression between the two central protrusions 60.

[0124] The two orifices 62 and 64 are positioned symmetrically at the ends of the plate 60.

[0125] The orifices 62 and 64 allow the passage of a screw 70 which is part of the fasteners 54 or 56.

[0126] As can be seen in the exploded perspective view of Figure 4, each fastener 54 or 56 includes the screw 70 and two nuts 72 and 74.

[0127] By tightening the two screws 70, it is ensured that the battery 12 positioned between the two central protrusions 60 is held with appropriate pressure.

[0128] To facilitate such screwing, the length of the plates 58 is such that the fasteners 54 and 56 are outside the cavity 30. This means that the length of each plate 58 is much greater than the length Z of the resonator 38. The sample holder 32 is made of polyoxymethylene (more often referred to by the abbreviation POM).

[0129] Such a polymer exhibits good rigidity while having the property of exhibiting a relative absence of mechanical stress when tightening fasteners and being silent in RPE.

[0130] Finally, it can be noted that electrical wires connected here to a galvanostatic device allow the aging of battery 12 to be controlled.

[0131] The set of elements just described forms an EPR spectrometer or imager.

[0132] It can be noted here before explaining the role of calculator 34 that the elements of the EPR spectrometer are not exhaustive.

[0133] In particular, the EPR spectrometer may include other elements such as an adapter, a waveguide or a circulator.

[0134] Calculator 34 is designed to analyze the waves detected by detector 28 in order to monitor the aging of the electrochemical element.

[0135] As an example here, calculator 34 is specifically designed to determine the presence or absence of an abnormal structure.

[0136] More generally, the calculator 34 is designed to analyze the waves detected by the detector 28 in order to obtain at least one piece of information relating to the aging of the electrochemical element.

[0137] For example, at least one piece of information relating to the aging of the electrochemical element is chosen from the list consisting of a charge state of the electrochemical element, a parameter related to the aging of the electrochemical element, the presence or absence of an abnormal structure and the location of the abnormal structure, the abnormal structure preferably being a metallic aggregate or a dendrite.

[0138] Calculator 34 is adapted here to operate in real time.

[0139] Calculator 34 is an electronic circuit designed to manipulate and / or transform data represented by electronic or physical quantities in registers of calculator 34 and / or memories into other similar data corresponding to physical data in register memories or other types of display devices, transmission devices or storage devices.

[0140] As specific examples, the calculator 34 includes a single-core or multi-core processor (such as a central processing unit (CPU), a graphics processing unit (GPU), a microcontroller and a digital signal processor (DSP)), a programmable logic circuit (such as an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a programmable logic device (PLD) and programmable logic arrays (PLAs)), a state machine, a logic gate and discrete hardware components.

[0141] The operation of control system 10 is now illustrated with reference to a method of monitoring the health status of at least one electrochemical element.

[0142] The control process includes an acquisition step and an analysis step.

[0143] During the acquisition stage, the control system 10 acquires data relating to the electrochemical element by implementing an electron paramagnetic resonance technique in the L band.

[0144] As explained previously, the data includes a spectrum or an image.

[0145] For this, the acquisition step is implemented by emitting L-band electromagnetic waves towards cavity 30 and detecting the waves coming from cavity 30.

[0146] During the analysis stage, the calculator 34 analyzes the acquired data to detect the presence or absence of an abnormal lithium structure in the electrochemical element.

[0147] By definition, an abnormal structure is an aggregate of metal that appears in a partially irreversible way during cycling.

[0148] The abnormal structure detected is, for example, an aggregate of metallic lithium.

[0149] As an alternative or in addition, the abnormal structure detected is, for example, a lithium dendrite.

[0150] Lithium dendrites are metallic microstructures that form in the electrochemical system during the charging process. For example, lithium dendrites form when excess lithium ions accumulate on the surface of anode 16 and cannot be absorbed into the anode 16 in time.

[0151] To perform such a detection, the computer 34 looks, for example, for specific line shapes in a spectrum. These shapes correspond to anomalous structures.

[0152] Alternatively or in addition, calculator 34 can search for shifts in a spectral image, that is to say an image representing the spatial variation of a spectrum.

[0153] To illustrate this process, one can refer to Figure 7, which shows an example of a spectrum obtained at different charge states for a lithium-ion battery with an NCA LFP mixture (graphite in pouch form), and to Figure 9 (left side), which shows an example of an EPR spectrum obtained for an all-solid-state NMC II Li° battery in the pristine state. The spectroscopic signature of the EPR signal from the lithium-ion battery exhibits, during cycling, a single line centered at a g-factor close to that of the free electron (2.0023), indicating the presence of lithium graphite complexes.

[0154] The spectroscopic signature of the EPR spectrum of the all-solid battery exhibits a simple peak centered at a g factor close to 2.0023 with a line width of the order of 0.3mT, as theoretically expected for metallic lithium Li°.

[0155] This positive result is reinforced by the overall appearance of the signal, i.e., the ratio between the positive and negative amplitudes of the spectrum, which exhibits an asymmetrical character. Such signal asymmetry is generally observed in conductive samples and is caused by the penetration of the electromagnetic wave into the metal.

[0156] This shows that the control process is indeed capable of characterizing 12 batteries in operation.

[0157] Other experimental results described in the "EXPERIENCES" section confirm this point.

[0158] It is therefore possible to insert a standard battery directly inside the resonator 38 without prior preparation of the sample (without opening the cell) and without developing model electrochemical cells.

[0159] The control system 10 provides real-time access under operating conditions to the graphite lithiation process and to the nucleation, morphology and distribution of these metallic impurities.

[0160] This analysis is available during battery charging or discharging.

[0161] The control system 10 is therefore particularly suited to the EPR characterization of industrial lithium-ion and all-solid-state L-band batteries.

[0162] In particular, cavity 30 and sample holder 32 are specifically adapted for such use.

[0163] The control system 10 thus makes it possible to easily control any anomaly or any form of premature aging of a battery 12 in the form of an inoperative pouch.

[0164] Other embodiments of the control system 10 benefiting from the previous advantages are conceivable such as, for example, L-band EPR analysis of cylindrical or prismatic batteries.

[0165] For example, the sample holder 32 is made of polyetheretherketone.

[0166] Such a polymer is often designated by the abbreviation PEEK, referring to the corresponding English name PolyEtherEtherKetone. More generally, the sample holder 32 is made of a material exhibiting good rigidity and containing no elements detectable by EPR. Good rigidity corresponds to a stiffness between 100 MPa and 200 MPa.

[0167] To enhance control of the pressure applied to the battery 12, the fasteners 54 and 56 of the sample holder 32 may each include a spring.

[0168] Each spring is then adapted to apply a force determined by its spring constant.

[0169] In each case (screw and / or spring), the fasteners 54 and 56 of the sample holder 32 allow the retaining elements 50 and 52 to be kept under pressure.

[0170] The control system 10 may also include a temperature control unit for the internal volume of the resonator 38.

[0171] For example, the control unit is any temperature control system that allows the performance of 12 batteries to be analyzed within a range of -40°C to 60°C.

[0172] EXPERIENCES

[0173] The Applicant was able to show that control system 10 allows for satisfactory results in several experiments which are now described.

[0174] These experiments are illustrated in Figures 7 to 10, which are now briefly described: Figures 7 and 8 show a graph of an example of an experimentally obtained L-band EPR spectrum at full charge and room temperature for an aluminized lithium-ion pouch battery with an NCA LFP (positive electrode) versus graphite (negative electrode) mixture. The inset represents the L-band EPR spectrum obtained after the formation of a solid electrolyte interphase, a step essential for the proper functioning of lithium-ion batteries. (Top of Figure 8) Electrochemical and current profile curves. The battery was charged and discharged at a C / 10 rate, corresponding to a theoretical displacement of 1 Li per unit of LiFePO4 in 10 hours, and then at a C / 2 rate (1 Li per unit of LiFePO4 in 2 hours). P1 represents a period during which the potential is 3.8V.(Bottom of figure 8) Evolution, under operating conditions, of the intensity of the RPE signal.

[0175] - Figure 9 shows the L-band EPR spectra of two all-solid-state batteries in aluminized pouches, obtained experimentally by the applicant. On the left is the spectroscopic signature of an NMC||Li° battery, and on the right is the spectroscopic signature of an NMC||Si-based battery. - [Fig. 10] Figure 10 shows the in-situ EPR images of an all-solid-state NMC||Li° battery in the three spatial planes (XY, ZX, and YZ planes).

[0176] Experimental protocol

[0177] Samples

[0178] A lithium-ion battery was assembled in a glove box with a positive electrode (cathode) made of an NCA LFP mixture and a negative electrode (anode) made of graphite. A liquid electrolyte was used in this type of technology.

[0179] Two types of all-solid-state battery were assembled using the same positive electrode and separator layers with a negative electrode based on Li-metal or silicon (Si).

[0180] An argyrodite-type sulfide electrolyte was selected as the solid electrolyte (SE).

[0181] The positive electrode, separator and Si-based negative electrode were all prepared by wet process using isobutylisobutylene and xylene solvents with a PVdF-based copolymer as binders for the electrodes and a specific internal binder for the separator.

[0182] All materials were handled and processed in a glove box filled with Ar.

[0183] For the positive electrode, Li-Nb-O-coated NMC and SE powders were dispersed in a binding gel solution using a planetary mixer. A suspension containing NMC, SE, and PVdF was applied to a carbon-coated aluminum foil with a squeegee at a density of 20.5 mg / cm². 2 .

[0184] For the Si-based negative electrode, µm-sized Si, SE, and Super P were dispersed in the bonding gel solution. A suspension containing Si, SE, C, and PVdF was applied to a carbon-coated Cu foil with a squeegee and a charge of 2.9 mg / cm² 2 has been obtained.

[0185] For the separator, the SE powder was dispersed in the binding gel solution; and the resulting SEJiant suspension (weight ratio 97:3) was applied to a PET film with a squeegee.

[0186] All the diapers were dried at room temperature in the glove compartment.

[0187] The uncalendered separator had a thickness of 130 pm (± 10 pm) and could be peeled from the PET film to recover a self-supporting solid electrolyte layer.

[0188] The 60 pm thick Li metal comes from the supplier Honjo.

[0189] The different layers were punched. The positive and negative electrodes were welded to tabs and placed in the laminated aluminum covered with polypropylene (PP), before sealing the resulting pouch.

[0190] The pouch was compacted under 300 MPa using a cold isostatic press to densify the layers and improve electrode / separator contact. The voltage was then controlled to ensure that the pouches were not short-circuited.

[0191] Electron paramagnetic resonance spectroscopy

[0192] The continuous wave EPR experiments were performed using a Bruker L-band spectrometer operating at a microwave excitation frequency of 1.01 GHz. The EPR measurements were carried out at room temperature in a cylindrical loop-gap microwave cavity.

[0193] The microwave power applied in the loop cavity 30 was set to 14mW for the lithium-ion battery and 36mW for the all-solid-state battery.

[0194] The modulation amplitude of the magnetic field was taken to be 0.3 mT.

[0195] The other spectrometer settings were as follows:

[0196] • scanning width: 200 G;

[0197] • conversion time: 40 ms;

[0198] • Number of analyses: 1;

[0199] • Scan time; 40.96 ms.

[0200] The simulations were performed using the EasySpin package for MATLAB to ensure the presence of a single, unique contribution in the RPE signals observed in the case of lithium-ion and all-solid-state batteries. For this purpose, a simple phase-shifted Lorentzian function was used.

[0201] Electron paramagnetic resonance imaging

[0202] RPE imaging measurements were performed with a Bruker imager operating in L-band and equipped with a three-axis gradient coil defined with gradients along the X-axis (perpendicular to Y and H). o ), of the Y axis (perpendicular to X and H o ) and the Z-axis. (along H o ).

[0203] The images were made with a gradient force of 42 G / cm and a field of view of 30 mm.

[0204] The high-resolution images were reconstructed with a size of 512 x 512 pixels, resulting in a pixel size of 150 pm.

[0205] The projections recorded under gradient were deconvolved from a signal obtained without gradient. Finally, the spatial images were obtained after a filtered backprojection.

[0206] Results and discussions

[0207] Low-frequency EPR experiments were performed to probe the electrode materials of a lithium-ion battery and two all-solid-state batteries.

[0208] The batteries in their pouches were measured in situ in pristine condition for all-solid-state batteries and in real time and operating conditions for the lithium-ion battery without opening them.

[0209] The pouches (size 65 x 38 mm) are placed in the microwave loop cavity 30 (diameter ~ 40 mm; length ~ 70 mm) in such a way that the plane of the battery 12 is oriented along the static magnetic field, i.e. perpendicular to the Y axis.

[0210] However, probing conduction electrons in metallic structures is not trivial due to the limited penetration of microwaves into the conductor, also known as skin depth S mw .

[0211] Indeed, it is well known that the shape of the EPR lines of metallic conductors is sensitive to the thickness of the metal and the depth of the skin. If the thickness of the conductive metal is greater than 3 mw Only the spins located at this depth are excited by the electromagnetic wave, generating an asymmetric spectroscopic signature known as Dysonian, characterized by the ratio A / B (A and B being the positive and negative amplitudes of the EPR signal, respectively). Conversely, if the metal thickness is less than 3 mw , all spins are excited and the EPR spectrum appears purely symmetric, A / B=1 , also called Lorentzian.

[0212] This skin depth can be easily calculated from the equation defined by:

[0213] Or :

[0214] • p is the metallic resistivity, and

[0215] • f denotes the microwave frequency applied in cavity 30.

[0216] We can see that the depth of the skin is proportional to 1. This implies that the lower the microwave excitation frequency, the deeper the skin. mw is big.

[0217] However, the physical size and conductive behavior of the laminated aluminum pouch present an additional challenge for monitoring electrode materials. Indeed, placing a large metallic conductor inside a standard 30-microwave X-band cavity can cause severe dielectric disturbances, making it impossible to tune the cavity.

[0218] However, achieving optimal settings is essential for performing EPR measurements.

[0219] Therefore, L-band EPR spectroscopy and imaging was used with a 38-loop-gap resonator adapted to standard 21 pouches, i.e., without specific 12-battery preparation.

[0220] In such a resonator 38, the electric field E is confined to the capacitive air gap and the magnetic field B within the inductive loop. Consequently, with such a loop-gap cavity, the dielectric is slightly disturbed upon insertion of the metallic sample, without hindering the adjustment of the EPR spectrometer.

[0221] Figure 7 shows an example of using L-band EPR to monitor, in real time and under operating conditions, the electrochemical processes occurring inside a lithium-ion battery containing an NCA LFP mixture (graphite wrapped in a standard aluminized bag). A crucial step in ensuring the safety and proper operation of a lithium-ion battery is stabilizing the liquid organic electrolyte through the formation of a passivation layer at the interface between the electrolyte and the negative electrode surface, known as the Solid Electrolyte Interface (SEI). Once this step is completed, the battery can undergo a series of charge and discharge cycles.

[0222] The inset in Figure 7 shows the experimentally obtained EPR spectrum after SEI formation. It is featureless, consistent with the pure graphite nature of the anode. In contrast, during battery charging, also known as the graphite lithiation period, an EPR spectrum appears with a g-factor close to that of the free electron (2.0023). This asymmetrical signal is consistent with the formation of lithium-containing graphite complexes (Li₂). xC6 corresponds to the lithiation of the graphite anode. During battery charging, this signal increases in intensity and reaches a maximum value corresponding to a highly lithied state of the graphite anode (Figure 8, bottom). During discharge, also called the graphite delithiation stage, the anode returns to its original state of pure graphite, characterized by a decrease in RPE intensity, which reaches a value close to 0 at the end of the discharge. This result demonstrates the good reversible behavior of graphite lithiation during electrochemical cycling, a well-known characteristic of these systems.

[0223] Figure 9 (left side) shows the L-band EPR spectrum of an NMCH Li° battery recorded at room temperature and in continuous wave mode through the standard aluminum laminate packaging. This signal exhibits a Dysonian line shape, which is commonly observed for conduction electrons.

[0224] To obtain more information on the nature of these metallic complexes such as the g factor and line width, the applicant simulated the spectrum with a phase-shifted Lorentzian function modeling the dysonian shape.

[0225] We can see that the EPR spectrum is characterized by:

[0226] (i) a single line centered on a g factor of approximately 2.004 ± 2,

[0227] (ii) a peak-to-peak line width of 0.3 mT,

[0228] (iii) an asymmetric A / B ratio around 3.7, as expected for metal structures.

[0229] It should be noted that the skin depth is approximately 4 pm for Li° complexes at 1 GHz.

[0230] This result indicates that the size of the detected metallic structure is well over 4 pm, which corresponds to the dimensions of the metallic electrode.

[0231] The NMClILi all-solid-state battery 0being composed of a metallic lithium electrode, the spectral signature can be compared to that of a non-metallic battery taken as a reference.

[0232] The result is visible on the right side of Figure 9 where the lithium of the metallic anode is replaced by a Si-based electrode.

[0233] As expected, initially the all-solid-state battery was based on NMC11Si, which contains Li + (Silent RPE), Ni 2+ (S=1), Neither 3+ (S=1 / 2), Mn 4+ (S=3 / 2), Co3 + (diamagnetic) and O 2- (silent RPE), does not give any spectrum of pristine metallic lithium.

[0234] However, at room temperature, NMC exhibits an EPR signal centered on a g value of approximately 2.00 with a linewidth of approximately 22 mT originating from Mn ions 4+ .

[0235] The presence of Ni 2+ and Neither 3+in the NMC sample is known to create an additional spectral broadening of the Mn peak 4+ .

[0236] The presence of Mn 4+ corresponds to a distortion of the baseline clearly visible for the NMC1Li-based battery but invisible for the NMC1Li battery 0 due to the intense signal from Li°.

[0237] Nevertheless, only one EPR peak is observed, showing a g factor close to the g value of the free electron (g e (= 2.0023), characteristic of the presence of SiO2 defects in the anode. In order to verify that the spectrum of metallic lithium does not originate from an impurity inside the pouch, the Applicant used imaging of the all-solid-state NMCH Li° battery to locate the anodic part.

[0238] As previously mentioned, the metallic structures of lithium give a relatively clear spectrum with a linewidth of the order of 3 G (with 0.1 mT = 1 G).

[0239] Using a gradient force of 42 G / cm and thanks to the sharp Li° line, high-resolution EPR images in the XZ, YZ and YX spatial planes respectively are expected.

[0240] After placing the pouch directly in the center of the microwave loop cavity 30 and gradient coils, each image was recorded at room temperature.

[0241] The time required for each image is approximately 60 minutes with a pixel size of 150 pm and a field of view of 30 mm.

[0242] Figure 10 shows the RPE images for an all-solid NMCHLi battery case 0 , respectively in the XZ plane (top left), the YZ plane (bottom left) and the YX plane (bottom right) respectively.

[0243] Unlike recent studies using X-band EPR imaging to monitor an electrochemical battery, where the packaging was made with a non-standard material, such as Kapton film, the L-band image contains the spin distribution of the electrode materials directly through the pouch 14.

[0244] The Li° anode part of the battery is clearly visible and appears in a square shape (15 mm x 15 mm) in the center of the image.

[0245] Within the limits of the resolution of an L-band EPR spectrometer, this shape and its dimension are similar to the actual size of the anode.

[0246] However, a slight variation in EPR intensities is observed, characterized by a much higher apparent amplitude at the anode edge. The physical origin of this non-uniform intensity stems from a local variation in the microwave field caused by shielding effects and / or eddy currents.

[0247] Furthermore, in Figure 10 (top left), a strong curved shape localized at X = -6 mm and Z = -6 mm, corresponding to the highest amplitude, can be observed. This result indicates a local defect much more sensitive to the microwave field, corresponding to the interface between the lithium electrode and the copper current collector.

Claims

DEMANDS 1. In-operando and non-destructive testing system (10) for the aging of at least one electrochemical element of a battery (12), the in-operando and non-destructive testing system (10) comprising: - a cavity (30), - a source (24) configured to emit L-band electromagnetic waves towards the cavity (30), the cavity (30) comprising a cylindrical resonator (38) with a circular base having at least one longitudinal cutout (46, 48), - a detector (28) suitable for detecting waves coming from the cavity (30), and - a computer (34) capable of analyzing the waves detected by the detector (28) to obtain at least one piece of information relating to the aging of at least one electrochemical element.

2. In operando and non-destructive testing system according to claim 1, wherein the source (24) is configured to emit electromagnetic waves having a frequency between 0.99 GHz and 1.10 GHz.

3. In operando and non-destructive testing system according to claim 1 or 2, wherein the resonator (38) delimits an internal volume (44) dimensioned to accommodate an accumulator (12) having a pouch shape, a prismatic shape or a cylindrical shape.

4. In operando and non-destructive testing system according to any one of claims 1 to 3, wherein the circular base of the cylindrical shape of the resonator (38) has a radius, the radius being greater than or equal to 1 centimeter, preferably greater than or equal to 3 centimeters, advantageously greater than or equal to 5 centimeters.

5. In operando and non-destructive testing system according to any one of claims 1 to 4, wherein the cavity (30) is provided with a sample holder (32) for holding the accumulator (12) in position.

6. In operando and non-destructive testing system according to claim 5, wherein the sample holder (32) has two retaining elements (50, 52) adapted to cooperate together to maintain the accumulator (12) in a central position in the internal volume (44).

7. In operando and non-destructive testing system according to claim 6, wherein the retaining elements (50, 52) are held under pressure by fasteners (54, 56).

8. In operando and non-destructive control system according to any one of claims 1 to 7, wherein the control system (10) further comprises a temperature control unit for the internal volume (44) of the resonator (38).

9. In operando and non-destructive testing system according to any one of claims 1 to 8, wherein at least one piece of information relating to the aging of at least one electrochemical element is chosen from a list consisting of a charge state of at least one electrochemical element, a parameter related to the aging of at least one electrochemical element, the presence or absence of an abnormal structure and the location of the abnormal structure, the abnormal structure preferably being a metallic aggregate or a dendrite.

10. In operando and non-destructive method for monitoring the aging of at least one electrochemical element of a battery (12), the monitoring method comprising the following steps: - emission of L-band electromagnetic waves towards a cavity (30), the cavity (30) comprising a cylindrical resonator (38) with a circular base having at least one longitudinal cutout (46, 48), - detection of waves coming from the cavity (30), and - analyze detected waves to obtain at least one piece of information relating to the aging of at least one electrochemical element.

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