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

Abstract

System and method for non-destructive monitoring of the aging of a battery in operation. The present invention relates to an in-operando, non-destructive monitoring system (10) for the aging of at least one electrochemical element of a battery. The in-operando, non-destructive monitoring system (10) comprises: - 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) adapted to detect the waves emanating from the cavity (30), and - a computer (34) adapted to analyze 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. Figure for the abstract: Figure 1

Description

Title of the invention: System and method for non-destructive testing of the aging of a battery in operation. TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to an in-operando and non-destructive system for monitoring the aging of a battery. The present invention also relates to an associated monitoring method. BACKGROUND OF THE INVENTION

[0002] Typically, a battery comprises one or more current storage cells, also called electrochemical generators, 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 face of electrodes arranged in the battery. The electrical energy is produced by electrochemical reactions during discharge of the battery. The electrodes, arranged in a container, are electrically connected to current output terminals that ensure electrical continuity between the electrodes and an electrical load to which the battery is connected.

[0003] To increase the delivered capacity, several sealed accumulators can be connected together to form a battery. Thus, a battery can be divided into modules, each module being composed of one or more accumulators connected together in series and / or in parallel. For example, a battery may comprise one or more parallel branches of accumulators connected in series and / or one or more parallel branches of modules connected in series.

[0004] A charging circuit is generally provided to which the battery can be connected to recharge the accumulators.

[0005] In the remainder of this application, we will use the more general term battery to describe the electrochemical system.

[0006] Furthermore, an electronic management system comprising measurement sensors and an electronic control circuit, more or less sophisticated depending on the application, can be associated with the battery. Such a system makes it possible, in particular, to organize and control the charging and discharging of the battery, in order to balance the charging and discharging of the different cells of the battery with respect to each other.

[0007] It is therefore desirable to be able to monitor the cycling (i.e., the succession of charges and discharges) of a battery in real time. This allows access to all types of information, including the state of charge and the aging of the battery such as the nucleation of lithium dendrites.

[0008] 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), makes it possible to follow in real time and under operating conditions the electrochemical evolution (redox processes and degradation processes) involved in a battery.

[0009] Conventionally used X-band EPR spectrometers can only analyze samples with a small size, which prevents the use of a commercial battery due to its size.

[0010] 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 effectively unusable.

[0011] In this sense, the known technique is destructive to a commercial battery because the battery needs to be opened. Summary of the invention

[0012] There is therefore a need for a non-destructive control system for the aging of a battery which can be implemented in operando with any type of battery, in particular a lithium-ion battery or any solid used commercially and regardless of its shape (pouch, prismatic or cylindrical).

[0013] To this end, the description describes an in operando and non-destructive aging control system for at least one electrochemical element of a battery, the in operando and non-destructive control system comprising:

[0014] - a cavity,

[0015] - a source configured to emit L-band electromagnetic waves at destination of the cavity, the cavity comprising a cylindrical resonator with a circular base having at least one longitudinal cutout,

[0016] - a detector suitable for detecting waves emanating from the cavity, and

[0017] - a computer suitable for analyzing the waves detected by the detector in order to obtain at least one piece of information relating to the aging of at least one electrochemical element.

[0018] The testing system is non-destructive in the sense that the physicochemical properties of the electrode materials present 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.

[0019] The control system is an in operando 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 (lithiated graphite, dendrite or plating).

[0020] 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.

[0021] According to particular embodiments, the control system has one or more of the following characteristics, taken individually or in all technically possible combinations:

[0022] - the source is configured to emit electromagnetic waves exhibiting a frequency between 0.99 GHz and 1.10 GHz.

[0023] - the resonator delimits an internal volume sized to accommodate a accumulator having a pouch shape, a prismatic shape or a cylindrical shape.

[0024] - 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.

[0025] - the cavity is equipped with a sample holder intended to hold the accumulator in position.

[0026] - the sample holder comprises two retaining elements designed to cooperate together to maintain the accumulator in a central position within the internal volume.

[0027] - the retaining elements are held under pressure by fasteners.

[0028] - the control system further comprises a temperature control unit of the internal volume of the resonator.

[0029] - at least one piece of information relating to the aging of at least one element electrochemical is chosen from the 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.

[0030] The description also relates to an in operando and non-destructive method for monitoring the aging of at least one electrochemical element of a battery, the monitoring method comprising the following steps:

[0031] - 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,

[0032] - detection of waves emanating from the cavity, and

[0033] - analyze detected waves to obtain at least one piece of information relating to the aging of at least one electrochemical element.

[0034] In this description, the expression "specific to" means interchangeably "suitable for", "adapted to" or "configured for". Brief description of the drawings

[0035] Some 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:

[0036] - [Fig.1] [Fig.1] is a schematic representation of a non-control system destructive to battery aging,

[0037] - [Fig.2] [Fig.2] is a view of an example of a battery in pouch form,

[0038] - [Fig.3] [Fig.3] is an exploded perspective view of the battery in [Fig.2],

[0039] - [Fig.4] [Fig.4] is an exploded perspective view of a sample holder used in the control system of [Fig. 1],

[0040] - [Fig. 5] [Fig. 5] is a representation of the positioning of a battery under pouch shape in the sample holder of [Fig.4],

[0041] - [Fig.6] [Fig.6] is a representation of the positioning of the sample holder with a battery in part of the control system of the [Fig.1],

[0042] - [Fig.7][Fig.8][Fig.9][Fig.10] Figures 7 to 10 are figures showing experimental results obtained by the Applicant.

[0043] DETAILED DESCRIPTION OF PREFERRED EMBODIMENT MODES

[0044] A control system 10 is schematically represented in [Fig.1].

[0045] The control system 10 is suitable for controlling an accumulator 12 which is here a battery 12.

[0046] In this case, without limitation, battery 12 is in the form of a pouch.

[0047] This format is often referred to by the corresponding English name "pouch" and is particularly interesting for its small size, low weight and ease of being produced in different shapes and sizes.

[0048] In a manner known per se, a battery 12 is generally an arrangement of a plurality of electrochemical elements but in the interest of simplifying the subject, a case with a single electrochemical element is described in what follows, knowing that the transposition to other arrangements is immediate.

[0049] The battery 12 comprises an electrochemical element and an electrochemical element management system.

[0050] As explained previously, an electrochemical element is an electricity-producing device in which chemical energy is converted into electrical energy.

[0051] The electrochemical element therefore delivers a current and a voltage between two terminals.

[0052] 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.

[0053] Preferably, however, the battery 12 is a lithium-ion battery or an all-solid-state battery.

[0054] The management system is a system specific to managing the electrochemical element.

[0055] An example of a battery 12 in the form of a standard aluminized pouch is visible in figures 2 and 3.

[0056] The battery 12 has a rectangular wall 14 encompassing the elements of [Fig.3], namely an anode 16, a cathode 18 and a separator 20.

[0057] The wall 14 forms a pocket 21 visible on the [Fig.2].

[0058] The wall 14 here has dimensions on the order of several centimeters.

[0059] 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.

[0060] The wall 14 is made of a deformable material, [Fig.2] showing a pocket 21 in which the electrochemical element is placed.

[0061] The wall material 14 comprises metallic elements, typically aluminium.

[0062] For example, the wall 14 is an aluminium film, preferably laminated.

[0063] The control system 10 is suitable for controlling all forms of aging during the cycling of the electrochemical element contained inside the wall 14.

[0064] Aging control here takes on many different aspects, from the control of redox reactions in battery 12 to the formation of dendrites in the electrochemical element. Several examples will become apparent upon reading this description.

[0065] Furthermore, the control system 10 is a non-destructive control system since the control system 10 can operate on a battery without opening it (i.e. without removing its packaging).

[0066] For this purpose, the control system 10 exploits electron paramagnetic resonance (EPR).

[0067] 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, in particular, allows observation of microwave absorption by paramagnetic or conductive systems when subjected to an intense magnetic field.

[0068] 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.

[0069] The principle of the EPR technique is based on the Zeeman effect: when subjected to the action of 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 ms (m = -S, -S+1, -S+2,..., S). This separation of levels is greater the more intense H is.

[0070] Thus, for the case of a single unpaired electron (i.e., for which S = 1 / 2), the presence of the external magnetic field gives rise to (2S + 1) = 2 electronic subspaces, corresponding to ms = -1 / 2 and ms = +1 / 2. The EM magnetic energy associated with each of these states is given by the following formula:

[0071] EM = ms*g*nB*H

[0072] Where: • £ is the postman of Landé, • is the Bohr magneton, and • H is the amplitude of the magnetic field.

[0073] 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 2 levels concerned, i.e. g^fi^H^, is equal to hv. It is at this particular value of H that a resonance phenomenon occurs.

[0074] In the example of [Fig.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 [Fig.1] for ease of visibility) and a computer 34.

[0075] The source 24 is suitable for exciting the cavity 30 with L-band electromagnetic waves.

[0076] The L band includes frequencies between 0.9 GHz and 2 GHz.

[0077] Preferably, the wave emitted by the source 24 is between 0.99 GHz and 1.10 GHz

[0078] Source 24 is therefore a microwave source.

[0079] The measurements or images in EPR are performed in continuous or pulsed mode. For the following purposes, without limitation, only the continuous mode is considered, so that the source 24 is considered here as a continuous source.

[0080] The magnetic field generator 26 is suitable for applying a static magnetic field in the cavity 30.

[0081] The magnetic field generator 26 is, for example, a set of current-supplied coils, the current control allowing control of the amplitude of the static field in the cavity 30.

[0082] The magnetic field generator 26 is suitable for applying a static magnetic field in the cavity 30.

[0083] In the case of [Fig. 1], the magnetic field generator 26 is a set of current-supplied coils (two in this figure), the current control allowing control of the amplitude of the static field in the cavity 30.

[0084] The detector 28 is suitable for detecting waves coming from the cavity 30,

[0085] The waves from cavity 30 contain data relating to the electrochemical element.

[0086] In this case, these data make 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).

[0087] The detector 28 is thus suitable for detecting data relating to the electrochemical element.

[0088] According to the example in [Fig.1], the detector 28 is a detection diode.

[0089] The cavity 30 includes an enclosure 36 and a resonator 38.

[0090] The enclosure 36 surrounds the resonator 38 and thus serves as a shield.

[0091] The enclosure 36 has a cylindrical shape.

[0092] The base of this cylinder is a disk having a radius denoted R in the following.

[0093] The resonator 38 is intended to receive the battery 12 containing the electrochemical element to be studied.

[0094] This means that the resonator 38 delimits an internal volume configured to accommodate the pouch 21.

[0095] The resonator 38 has the shape of a cylinder with a circular base.

[0096] The generatrix of the cylinder is in a longitudinal direction corresponding to the axis marked X on the [Fig.1].

[0097] The other directions are noted as first transverse direction Y and second transverse direction Y.

[0098] The circular base corresponds to a disk having a radius denoted r in the following.

[0099] The resonator 38 has a length z (dimension along the longitudinal direction X).

[0100] 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.

[0101] In [Fig.2], the X, Y and Z axes are shown to illustrate how the battery 12 is inserted into the internal volume 44.

[0102] The length of the wall 14 of the battery 12 is along the longitudinal direction X while the width of the wall 14 is along the second transverse direction Z.

[0103] 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.

[0104] This inter-wall distance corresponds to the thickness of the resonator 38.

[0105] The thickness of the resonator 38 is denoted w.

[0106] According to the example described, the resonator 38 has two longitudinal cutouts 46 and 48.

[0107] Each cutout 46 and 48 has the same shape and extends from one end to the other of the resonator 38

[0108] Each cutout 46 and 48 has a width t.

[0109] The two cutouts 46 and 48 are placed symmetrically with respect to the center of the resonator 38.

[0110] Thus, the resonator 38 has the shape of two arcs of circles separated by an interval.

[0111] Because of this arrangement, such a resonator 38 is often called a "loop-gap", which literally means loop-interval, the term "loop" referring to the arcs of circles and the term "gap" referring to the space formed by each cutout.

[0112] Given that the internal volume of the resonator 38 is sized to accommodate a pouch 21 (corresponding to an industrial battery of a commonly used format), 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.

[0113] In operation, as seen in the enlarged view of [Fig.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).

[0114] The sample holder 32 comprises two retaining elements 50 and 52 and two fasteners 54 and 56.

[0115] The two retaining elements 50 and 52 cooperate together to hold the battery 12 in a central position.

[0116] In addition, this cooperation makes it possible to precisely control the pressure applied to the battery 12 during an electrochemical cycle to maintain good contact between the different materials present inside the pouch 21 forming the battery 12.

[0117] According to the example described, the two retaining elements 50 and 52 have the same shape.

[0118] Each retaining element 50 and 52 comprises a plate 58 having a central projection 60 and two orifices 62 and 64.

[0119] Plate 58 has a rectangular shape.

[0120] Each central projection 60 also has a rectangular shape.

[0121] When the battery 12 is positioned, it is held in the center by compression between the two central projections 60.

[0122] The two orifices 62 and 64 are positioned symmetrically at the ends of the plate 60.

[0123] The orifices 62 and 64 allow the passage of a screw 70 which is part of the fasteners 54 or 56.

[0124] As can be seen in the exploded perspective view of [Fig.4], each fastener 54 or 56 includes the screw 70 and two nuts 72 and 74.

[0125] By tightening the two screws 70, it is ensured that the battery 12 positioned between the two central protrusions 60 is held with an appropriate pressure.

[0126] To allow such screwing to be easily carried out, 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.

[0127] The sample holder 32 is made of polyoxymethylene (more often referred to by the abbreviation POM).

[0128] Such a polymer exhibits good rigidity while having the property of exhibiting a relative absence of mechanical stress when tightening the fasteners and of being silent in RPE.

[0129] Finally, it can be noted that electrical wires connected here to a galvanostatic device allow the aging of the battery 12 to be controlled.

[0130] The set of elements that have just been described forms an EPR spectrometer or imager.

[0131] It may be noted here before explaining the role of the calculator 34 that the elements of the EPR spectrometer are here non-limiting.

[0132] In particular, the EPR spectrometer may include other elements such as an adapter, a waveguide or a circulator.

[0133] The calculator 34 is suitable for analyzing the waves detected by the detector 28 in order to control the aging of the electrochemical element.

[0134] As an example here, the calculator 34 is suitable for determining the presence or absence of an abnormal structure.

[0135] More generally, the calculator 34 is suitable for analyzing 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.

[0136] For example, at least one piece of information relating to the aging of the electrochemical element is chosen from the list consisting of a state of charge 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.

[0137] Calculator 34 is here adapted to operate in real time.

[0138] The 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 in other similar data corresponding to physical data in register memories or other types of display devices, transmission devices or storage devices.

[0139] As specific examples, the computer 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.

[0140] The operation of the control system 10 is now illustrated with reference to a method for monitoring the health status of at least one electrochemical element.

[0141] The control process comprises an acquisition step and an analysis step.

[0142] During the acquisition step, the control system 10 acquires data relating to the electrochemical element by implementing an electron paramagnetic resonance technique in the L band.

[0143] As explained previously, the data includes a spectrum or an image.

[0144] For this purpose, the acquisition step is implemented by emitting L-band electromagnetic waves towards cavity 30 and detecting the waves coming from cavity 30.

[0145] During the analysis step, the computer 34 analyzes the acquired data to detect the presence or absence of an abnormal lithium structure in the electrochemical element.

[0146] By definition, an abnormal structure is an aggregate of metal which appears in a partially irreversible way during cycling.

[0147] The abnormal structure detected is, for example, an aggregate of metallic lithium.

[0148] As an alternative or in addition, the abnormal structure detected is, for example, a lithium dendrite.

[0149] Lithium dendrites are metallic microstructures that form in the electrochemical system during the charging process. For example, lithium dendrites form when additional lithium ions accumulate on the surface of the anode 16 and cannot be absorbed into the anode 16 in time.

[0150] To perform such a detection, the computer 34 searches, for example, for specific line shapes in a spectrum. These shapes correspond to anomalous structures.

[0151] Alternatively or in addition, the calculator 34 can search for shifts in a spectral image, that is to say an image representing the spatial variation of a spectrum.

[0152] To illustrate this process, it is possible to refer to [Fig.7] which illustrates an example of a spectrum obtained at different states of charge for a lithium-ion battery with an NCA LFPII graphite mixture in pouch form and to refer to [Fig.9] (left part) which shows an example of an EPR spectrum obtained for an all-solid NMC II Li° battery in pristine state.

[0153] The spectroscopic signature of the EPR signal from the lithium-ion battery exhibits, during cycling, a simple 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 linewidth of the order of 0.3mT, as theoretically expected for metallic lithium Li°.

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

[0156] This shows that the control method makes it possible to characterize batteries 12 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 12.

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

[0162] In particular, the cavity 30 and the 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 a pouch in operando.

[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 in reference to the corresponding English name PolyEtherEtherKetone.

[0167] More generally, the sample holder 32 is made of a material having the property of exhibiting good rigidity and not containing any element detectable by EPR. Good rigidity corresponds to a stiffness between 100 MPa and 200 MPa.

[0168] 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.

[0169] Each spring is then adapted to apply a force determined by its stiffness constant.

[0170] 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 held under pressure.

[0171] The control system 10 may also include a temperature control unit for the internal volume of the resonator 38.

[0172] For example, the control unit is any temperature control system that allows the performance of batteries 12 to be analyzed in a range between -40°C and 60°C. EXPERIENCES

[0173] The Applicant has been able to show that the control system 10 makes it possible to obtain 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 correspond to a graph showing 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 a solid electrolyte interphase formation process, an essential step for the proper functioning of lithium-ion batteries. (Top of [Fig. 8]) Electrochemical and current profile curves. The battery was charged and discharged at a C / 10 rate, corresponding to a theoretical displacement of ILi per unit of LiFePO4 in 10 hours, and then at a C / 2 rate (ILi per unit of LiFePO4 in 2 hours). PI represents a period during which the potential is now at 3.8V. (Bottom of [Fig. 8])8]) Evolution, under operating conditions, of the intensity of the RPE signal.

[0175] - [Fig. 9] represents the L-band EPR spectra of two pocket batteries all-solid aluminized obtained experimentally by the applicant, with on the left the spectroscopic signature of an NMCIlLi0 battery and on the right the spectroscopic signature of an NMCIISi-based battery.

[0176] - [Fig. 10] [Fig. 10] shows the in-situ images obtained by EPR of a battery All-solid NMCIlLiO in the three planes of space (XY, ZX, and YZ planes). Experimental protocol. Samples.

[0177] A lithium-ion battery has been assembled in a glove box with a positive electrode (cathode) of an NCA LFP mixture and a negative electrode (anode) of graphite. In this type of technology, a liquid electrolyte has been used.

[0178] Two types of all-solid-state battery were assembled using the same positive electrode and the same separator layers with a negative electrode based on Li-metal or silicon (Si).

[0179] An argyrodite-type sulfide electrolyte was selected as the solid electrolyte (SE).

[0180] The positive electrode, the separator and the 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.

[0181] All materials were handled and processed in a glove box filled with Ar.

[0182] For the positive electrode, Li-Nb-O coated NMC and SE powders were dispersed in a binding gel solution using a planetary mixer. A A suspension containing NMC, SE and PVdF was applied to a carbon-coated aluminum sheet with a squeegee with a charge of 20.5 mg / cm2.

[0183] For the Si-based negative electrode, Si (pm size), 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 was obtained.

[0184] For the separator, the SE powder was dispersed in the binding gel solution; and the resulting SEdiant suspension (weight ratio 97:3) was applied to a PET film with a squeegee.

[0185] All the layers were dried at room temperature in the glove box.

[0186] The uncalendered separator had a thickness of 130 µm (± 10 µm) and could be peeled from the PET film to recover a self-contained solid electrolyte layer.

[0187] The 60 pm thick Li metal comes from the supplier Honjo.

[0188] The different layers were punched.

[0189] The positive and negative electrodes were welded to tabs and placed in the polypropylene (PP) coated laminated aluminum, 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 carried out using a Bruker L-band spectrometer operating at a microwave excitation frequency of 1.01 GHz. The EPR measurements were performed 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 to 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: • scanning width: 200 G; • conversion time: 40 ms; • Number of analyses: 1; • Scanning time; 40.96 ms.

[0196] The simulations were performed using the EasySpin package for MATLAB to ensure the presence of a single 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.

[0197] Electron paramagnetic resonance imaging

[0198] 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 Ho), the Y axis (perpendicular to X and Ho) and the Z axis (along Ho).

[0199] The images were made with a gradient force of 42 G / cm and a field of view of 30 mm.

[0200] The high-resolution images were reconstructed with a size of 512 x 512 pixels, which gives a pixel size of 150 pm.

[0201] The projections recorded under gradient were deconvolved from a signal obtained without gradient.

[0202] Finally, the spatial images were obtained after filtered backprojection. Results and discussion

[0203] Low frequency EPR experiments were carried out to probe the electrode materials of a lithium-ion battery and two all-solid-state batteries.

[0204] The pouch batteries in situ were measured in pristine condition for all-solid batteries and in real time and operating conditions for the lithium-ion battery without opening them.

[0205] The pouches (size 65 x 38 mm) are placed in the microwave loop cavity 30 (diameter ~ 40 mm; length ~ 70 mm) such that the plane of the battery 12 is oriented along the static magnetic field, i.e. perpendicular to the Y axis.

[0206] However, probing conduction electrons in metallic structures is not trivial due to limited microwave penetration into the conductor, also known as the 8mw skin depth.

[0207] 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 conducting metal is greater than μmw, only the spins located at this depth are excited by the electromagnetic wave, generating an asymmetric spectroscopic signature known as Dysonian and characterized by the ratio A / B (A and B being respectively the positive and negative amplitudes of the EPR signal). Conversely, if the thickness of the metal is less than μmw, all the spins are excited and the EPR spectrum appears purely symmetrical, A / B=λ, also called Lorentzian.

[0208] This skin depth can be easily calculated from the equation defined by:

[0209] . / F Omw yf

[0210] Where: P is the metallic resistivity, and • f denotes the microwave frequency applied in cavity 30.

[0211] It can be seen that the skin depth is proportional to l / ^f. This implies that the lower the microwave excitation frequency, the larger dmw is.

[0212] However, the physical size and conductive behavior of the laminated aluminum pouch present an additional challenge for monitoring electrode materials.

[0213] Indeed, placing a large metallic conductor inside a standard X-band microwave cavity 30 can cause serious dielectric disturbances making it impossible to tune the cavity 30.

[0214] Nevertheless, obtaining an optimal setting is essential for performing EPR measurements.

[0215] Consequently, L-band EPR spectroscopy and imaging was used with a loop-gap resonator 38 adapted to standard pouches 21, i.e. without specific battery preparation 12.

[0216] 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.

[0217] 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 LFPII graphite mixture wrapped in a standard aluminized bag. An important step in ensuring the safety and proper functioning of a lithium-ion battery is stabilizing the organic liquid electrolyte through the formation of a passivation layer at the interface between the electrolyte and the negative electrode surface, a process known as the Solid Electrolyte Interface (SEI). Once this step is completed, the battery can be subjected to a series of charge and discharge cycles.

[0218] The inset in [Fig. 7] shows the experimentally obtained RPE spectrum after SEI formation. It is featureless, which is consistent with the pure graphite nature of the anode. In contrast, during battery charging, also called the graphite lithiation period, an RPE spectrum appears with a g-factor close to that of the free electron (2.0023). This asymmetric signal is consistent with the appearance of LixC6 lithianed graphite complexes corresponding to the lithiation of the graphite anode. During battery charging, this signal increases in intensity and reaches a maximum value corresponding to a highly lithianed state of the graphite anode (lower [Fig. 8]). During discharge, also called the graphite delithiation stage, the anode returns to its original pure graphite state, characterized by a decrease in RPE intensity, which reaches a value close to 0 at the end of the discharge. This result shows the good reversible behavior of graphite lithiation during electrochemical cycling, a well-known behavior of these systems.

[0219] Fig. 9 (left part) shows the L-band EPR spectrum of an NMC1Li0 battery recorded at room temperature and in continuous wave through the standard aluminum laminate packaging.

[0220] This signal exhibits a Dysonian line shape which is usually found for conduction electrons.

[0221] To obtain more information on the nature of these metal complexes such as the g factor and line width, the applicant simulated the spectrum with a phase-shifted Lorentzian function modeling the dysonian shape.

[0222] We can see that the EPR spectrum is characterized by: i. a single line centered on a g factor of approximately 2.004 ± 2, ii. a peak-to-peak line width of 0.3 mT, iii. an asymmetric A / B ratio around 3.7, as expected for metal structures.

[0223] It should be noted that the skin depth is approximately 4 pm for Li° complexes at 1 GHz.

[0224] This result indicates that the size of the detected metallic structure is well above 4 pm, which corresponds to the dimensions of the metallic electrode.

[0225] Since the all-solid-state NMCIlLi0 battery is composed of a metallic lithium electrode, the spectral signature can be compared with a non-metallic battery taken as a reference.

[0226] The result is visible on the right side of [Fig.9] where the lithium of the metallic anode is replaced by a Si-based electrode.

[0227] As expected, initially the all-solid-state NMCIISi-based battery, which contains Li+ (silent RPE), Ni2+ (S=l), Ni3+(S=l / 2), Mn4+(S=3 / 2), Co3+ (diamagnetic) and O2 (silent RPE), does not give any pristine metallic lithium spectrum.

[0228] However, at room temperature, NMC exhibits an EPR signal centered on a g value of about 2.00 with a linewidth of about 22 mT from Mn4+ ions.

[0229] The presence of Ni2+ and Ni3+ in the NMC sample is known to create an additional spectral broadening of the Mn4+ peak.

[0230] The presence of Mn4+ corresponds to a distortion of the baseline clearly visible for the NMCIISi-based battery but invisible for the NMCIlLi0 battery due to the intense signal from Li°.

[0231] Nevertheless, only one EPR peak is observed, showing a g factor close to the g value of the free electron (ge = 2.0023), characteristic of the presence of SiO2 defects in the anode.

[0232] In order to verify that the metallic lithium spectrum does not originate from an impurity inside the pouch, the Applicant used imaging of the all-solid-state NMCIlLi0 battery to locate the anodic part.

[0233] As previously stated, 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).

[0234] By 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.

[0235] After placing the pouch directly in the center of the microwave loop cavity 30 and gradient coils, each image was recorded at room temperature.

[0236] 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.

[0237] Fig. 10 presents the RPE images for an all-solid NMCIlLi0 battery pouch, respectively in the XZ plane (top left), the YZ plane (bottom left) and the YX plane (bottom right).

[0238] Unlike recent studies using X-band EPR imaging to monitor an electrochemical battery and in which 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.

[0239] The Li° anodic part of the battery is clearly visible and appears in a square shape (15 mm x 15 mm) in the center of the image.

[0240] Within the limits of the resolution of an L-band EPR spectrometer, this shape and its dimensions are similar to the actual size of the anode.

[0241] 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.

[0242] Furthermore, in [Fig. 10] (top left), an intense 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 control system (10) of the aging of at least one electrochemical element of a battery (12), the in operando and non-destructive control 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 cut (46, 48), - a detector (28) adapted to detect the waves from the cavity (30), and - a computer (34) adapted to analyze 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. An in operando and non-destructive testing system according to claim 5, wherein the sample holder (32) comprises two retaining elements (50, 52) designed 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 state of charge 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 to a cavity (30), the cavity (30) comprising a cylindrical resonator (38) with a circular base having at least one longitudinal cut (46, 48), - detection of the waves from the cavity (30), and - analysis of the detected waves to obtain at least one piece of information relating to the aging of at least one electrochemical element.

Images