Method for thermal characterization of a reference electrochemical cell of an electric battery

Abstract

The invention relates to a method for the thermal characterization of a reference electrochemical cell of an electric battery of the type comprising an envelope (10) within which is housed at least one stack (13) of positive and negative electrodes separated by a separator, the characterization method comprising in particular a step of internal and external instrumentation of at least one or more electrochemical test cell(s) (100, 101, 102) having an architecture identical to an architecture of the reference electrochemical cell, configured to determine together a vertical thermal gradient, a transverse thermal gradient and an average temperature. (Fig. 7)

Description

Title of the invention: Method for the thermal characterization of a reference electrochemical cell of an electric battery Technical field of the invention

[0001] The invention relates, in general, to the technical field of energy storage devices, and relates in particular to the manufacture of instrumented cells.

[0002] The invention relates more specifically to a method for the thermal characterization of a reference electrochemical cell of an electric battery. Prior art

[0003] Motor vehicles with electric or hybrid traction or propulsion include one or more battery modules connected to a power network to supply an electric motor (traction or propulsion).

[0004] The battery modules are grouped in a casing and together form a battery block, also often referred to by the English expression "battery pack", this casing generally containing a mounting interface and connection terminals.

[0005] Each battery module is an assembly comprising several electrochemical cells generating current by chemical reaction, for example of lithium-ion (or Li-ion), Ni-Mh, Ni-Cd or lead type.

[0006] An electrochemical cell comprises, in particular, a stack of positive electrodes connected to each other and a stack of negative electrodes connected to each other, separated by a separator, known as a "stack". The positive electrodes are connected to each other at a positive terminal, and the negative electrodes are connected to each other at a negative terminal.

[0007] It is known to assemble, in series and / or in parallel, a plurality of electrochemical cells in order to produce battery modules using an interconnection device ensuring electrical contact between the terminals of two neighboring electrochemical cells.

[0008] Each electrochemical stack is housed in a metal casing of the associated electrochemical cell. The casing is generally made of aluminum. Once the electrochemical stacks are integrated into a compartment of the casing, a plate forming a lid for the electrochemical cell is laser-welded to the compartment to create the structural connection and seal the electrochemical cell, thus closing the casing. In the remainder of this description, an electrochemical stack will also be referred to as a "stack" or "electrode stack".

[0009] Lithium-ion (Li-ion) batteries are currently the most widely used in electric vehicles. A Li-ion battery is a set of Li-ion accumulators, That is to say, the cells, connected in series or parallel in modules. The cells are cylindrical, prismatic, or pouch-type (or "pouch cells"). Recent advances in lithium-ion batteries have led to a significant reduction in battery prices and an increase in battery life.

[0010] To increase the range of electric vehicles, manufacturers have increased the onboard energy by increasing the size of the battery pack or by increasing the energy density of the batteries. The range of electric vehicles varies depending on the vehicle and driving conditions, but the energy densities of the batteries allow for driving several hundred kilometers in all cases.

[0011] To reduce charging times, manufacturers increase the power output of chargers. However, charging currents are limited by cell operating mechanisms, particularly thermal effects and aging. Beyond a certain operating range, increasing the charging current can lead to cell heating rather than a reduction in charging time. Rapid charging can cause degradation of lithium-ion cells through various mechanisms, including the deposition of metallic lithium ("lithium plating"), electrolyte degradation through the growth of a passive layer ("solid electrolyte interphase"), mechanical degradation of the electrodes, etc.

[0012] The temperature increase of Li-ion batteries can also lead to thermal runaway in one of the battery cells, with a domino effect on the other cells. Thermal runaway results in an increase in cell temperature, which causes an acceleration of exothermic reactions, generating a further increase in the internal cell temperature, with a risk of liquid electrolyte leakage, release of chemicals, fire, and explosion.

[0013] To increase the performance, safety, and durability of lithium-ion cells, it is necessary to better understand the internal parameters of the cells during operation. Indeed, to avoid stressing the cells, whether during charging or discharging, in hazardous areas, safety margins are used, particularly operating voltage ranges during charging and discharging. Another parameter that is monitored is temperature. During operation, the electrochemical processes within the cell generate heat. This heat must be efficiently dissipated by an external system.Therefore, when using lithium-ion batteries, it is advantageous to use an electronic control unit, generally called a BMS (for "Battery Management System"), which will limit the loads to optimize performance while ensuring battery safety and longevity. To do this, the system must be able to measure cell parameters in real time. make up the battery. The battery is indeed generally composed of several assembled cells and the BMS must manage all the cells of the battery.

[0014] To provide the BMS with control data, several measurements are taken on the cells or at the module level. Currently, the measurements taken generally include the external temperature of the cells, voltage, and current. However, this data is insufficient to obtain a precise picture of the phenomena occurring inside the cell and does not allow for anticipating degradation and associated risks. These measurements are taken by adding sensors to the cells (temperature, pressure, strain, acoustic sensors, etc.), but also inside the cells, using so-called internal sensors, either within the electrolyte or on the electrodes.

[0015] Even if such instrumented cells (equipped with sensors inside the cells) are not used on end-of-life vehicles, they allow for a better understanding of the phenomena internal to the cells, the creation of the most realistic "digital twins" possible for performing realistic simulations, and thus improving the predictability of phenomena to anticipate and avoid them. The BMS can then be configured to take into account these most realistic results possible and improve battery management while enhancing battery safety.

[0016] Studies and research on the performance of a battery therefore depend on the accuracy of the measurement of the main internal states of the battery, such as temperature gradients during operational scenarios and / or during the manufacture of the cells (filling, electrical formation for example) or the internal ohmic thermal contribution due to the components of the connectors.

[0017] Internal thermal gradients are present in the volume region of the electrode stack, which are masked by the cell's insulating base and the aluminum housing. In active cooling scenarios, significant thermal gradients can lead to heterogeneous current densities, which limits performance and, ultimately, cell aging.

[0018] Instrumented cells are specifically designed to measure internal thermal states during relevant power demands. By understanding the internal thermal behavior of cells during energy demands and within the framework of thermal management, improved optimization could be applied to various cell health states.

[0019] To ensure the product's representativeness, these instrumented cells must have an architecture whose operation is not hindered by the presence of the instrumentation. Therefore, a key challenge is to propose a methodology for implementing the instrumentation of internal cells that must not not to interfere with the operation of equipment for the design and assembly of battery prototypes.

[0020] Another problem concerns the implementation of a thermal characterization process of a reference electrochemical cell which allows optimal representativeness to be obtained without substantially multiplying the sensors. Description of the invention

[0021] The invention aims to remedy all or part of the drawbacks of the prior art by proposing in particular a solution allowing reliable characterization of a reference battery cell to be characterized, in particular to improve the development of performance optimization strategies such as those relating to BMS mapping.

[0022] In general, the invention aims to enable a better understanding of aspects related to cell safety, particularly those related to thermal runaway scenarios which become more predictable.

[0023] To this end, according to a first aspect of the invention, a method for the thermal characterization of a reference electrochemical cell of an electric battery of the type comprising an envelope inside which is housed at least one stack of positive and negative electrodes separated by a separator, the characterization method comprising: - an internal and external instrumentation step of at least one or more electrochemical test cell(s) having an architecture identical to that of the reference electrochemical cell, each being instrumented by: • a plurality of external instruments equipping the casing of the associated electrochemical test cell, on the outer side of the casing opposite the inner space; and • a plurality of internal instruments housed in the internal space of the associated envelope configured to determine a vertical thermal gradient with respect to a vertical reference axis contained in a reference plane parallel to the electrodes and, if the number of stacks is greater than or equal to two, a transverse thermal gradient with respect to a transverse reference axis perpendicular to the reference plane and / or an average temperature; - a step of setting up the instrumented test cell(s) on a test device; - a step of applying a predetermined constraint profile to the instrumented test cell(s); - a step of measuring and recording the measurements from the instruments during the step of applying the predetermined stress profile, so as to determine at least the vertical and transverse thermal gradients and the associated average temperature.

[0024] According to one embodiment, the reference electrochemical cell to be characterized comprises more than two electrode stacks, the instrumentation step comprises the internal and external instrumentation of two electrochemical test cells: - a first electrochemical test cell among the two instrumented electrochemical test cells comprising internal instruments configured to determine the vertical and transverse thermal gradients; and - a second electrochemical test cell among the two instrumented electrochemical test cells comprising internal instruments configured to determine the vertical thermal gradient and average temperature.

[0025] According to one embodiment, the reference electrochemical cell to be characterized comprises only one or two electrode stacks; the instrumentation step comprises the internal and external instrumentation of a single electrochemical test cell in which the internal instruments are configured to determine the vertical thermal gradient and: - the average temperature, if the reference electrochemical cell to be characterized comprises only a stack of electrodes; or - the transverse thermal gradient, if the reference electrochemical cell to be characterized comprises only a stack of electrodes

[0026] According to one embodiment, each instrumented test cell is equipped with at least three, preferably exactly three, internal instruments. This ensures the safety of the instrumented test cells by minimizing the impact of the instrumentation inside the electrochemical cell.

[0027] According to one embodiment: - The first electrochemical test cell among the two instrumented electrochemical test cells comprises a first internal instrument positioned in an area near a lower edge of a first electrode stack, a second internal instrument positioned in an area near an upper edge of the first electrode stack, opposite the lower edge, and a fourth internal instrument positioned in an area near an upper edge of a second stack of electrodes, preferably adjacent to the first stack of electrodes; - the second electrochemical test cell among the two instrumented electrochemical test cells includes a first internal instrument positioned in an area near a lower edge of a first electrode stack, a second internal instrument positioned in an area near an upper edge of the first electrode stack, opposite the lower edge, and a third internal instrument positioned in an area near a lateral edge of the first electrode stack.

[0028] According to one embodiment, the first stacks of the first and second instrumented electrochemical test cells are stacks adjacent to an associated parallel wall of the corresponding envelope. Tests have shown that this area is more representative of internal temperature gradients.

[0029] According to one embodiment, the casing of the instrumented electrochemical test cell comprises a prismatic housing, the housing comprising a cup having an opening closed by a lid.

[0030] According to one embodiment, the second and fourth internal instruments of the first electrochemical test cell and the second internal instrument of the second electrochemical test cell are located in an area close to a safety vent in the lid configured to allow degassing of the electrochemical cell in the event of internal pressure exceeding a threshold pressure.

[0031] According to one embodiment, each instrumented electrochemical test cell is equipped with at least eight, preferably exactly eight, external instruments.

[0032] According to one embodiment, for a given instrumented electrochemical test cell: - at least one of the external instruments, preferably a single external instrument, is positioned on the lid of the associated electrochemical test cell; - at least one of the external instruments, preferably a single external instrument, is positioned on a bottom of the cup of the associated electrochemical test cell; - a plurality of external instruments, preferably at least five external instruments, preferably exactly five external instruments, are positioned on one large face of the associated electrochemical test cell cup, the large face being parallel to the reference plane; and - at least one of the external instruments, preferably a single external instrument, is positioned on a small face of the cell cup associated electrochemical test, the small face being perpendicular to the reference plane.

[0033] According to one embodiment, the external instruments positioned on the large face of the cup of the associated electrochemical test cell are positioned on this single large face among the large faces of the cup of the associated cell, the large instrumented face corresponding to the large face adjacent to the first stack of the first or second corresponding electrochemical cell.

[0034] According to one embodiment, among the external instruments positioned on the large face of the cup of the associated electrochemical test cell: - three external lateral instruments are positioned so as to be vertically aligned along the large instrumented face and longitudinally centered with respect to the large instrumented face, these three external lateral instruments comprising an upper lateral instrument near the lid, a vertically centered middle lateral instrument, and a lower lateral instrument near the bottom of the cup; and / or - two external lateral instruments are positioned so as to be aligned vertically along the large instrumented face and being offset longitudinally, these two external lateral instruments comprising an offset lateral instrument superior near the lid, a offset lateral instrument median.

[0035] According to one embodiment, the small face of the electrochemical cell cup on which the external instrument is positioned corresponds to a face perpendicular to the lid and the bottom of the cup, the small face being chosen from among the small face closest to the safety vent of the lid configured to allow degassing of the associated electrochemical cell in the event of internal pressure exceeding a threshold pressure.

[0036] According to one embodiment, the instruments include sensors, preferably temperature sensors, even more preferably thermocouples.

[0037] According to one embodiment, the thermocouples of the internal instruments at least are configured so that each is compatible with an electrolyte of the associated electrochemical test cell.

[0038] According to one embodiment, each thermocouple is connected to one or more electrical linking means to connect it to a unit of measurement, comprising for example each one or more electrical cable(s).

[0039] According to one embodiment, the electrical connection means of the internal thermocouples are arranged so as to pass through the envelope of the associated electrochemical cell in a sealed manner, each of the electrical connection means having an at less a protective sheath configured to be resistant to an electrolyte of the associated electrochemical cell.

[0040] According to one embodiment, the cable(s) of the electrical connection means for linking the thermocouples, preferably the internal thermocouples, to the unit of measurement, comprise at least (preferably exactly) one pair of conducting wires wound helically around an axis of the cable they form. In other words, each cable forming an electrical connection means (at least those connected to the internal thermocouples) is formed by a twisted pair. In such a configuration, each conducting wire among the twisted wires is protected by an individual protective sheath. This individual protective sheath is configured to be resistant to an electrolyte of the associated electrochemical cell. Preferably, this protective sheath comprises, and is preferably made of, perfluoroalkoxy (PFA).

[0041] Thanks to this feature, the upward movement of electrolyte by capillary action is limited. Indeed, the sheaths of the thermocouple connecting means are both within the internal space of the cells and must also pass through the casing of the associated electrochemical cell in a sealed manner, preferably through the safety vent, to exit outside the casing, i.e., into the external space of the associated electrochemical cell. The use of electrolyte-resistant materials prevents the sheath from disintegrating inside the electrochemical cell casing. Having a twisted pair of wires, each protected by a sheath, means that if electrolyte escapes by capillary action, the "path" it must travel to exit the internal space will be longer, thus limiting the upward movement of electrolyte by capillary action. Brief description of the figures

[0042] Other features and advantages of the invention will become apparent from the following description, with reference to the accompanying figures, which illustrate: • [Fig.1]: a view of several successive stages of an assembly process of an electrochemical cell; • [Fig.2]: a view of an instrumented electrochemical battery test cell according to an example embodiment; • [Fig.3]: a view of the instrumented electrochemical test cell on a test device; • [Fig.4]: a view of a representation of a 3D thermal simulation of a prismatic cell subjected to rapid load stress with an active cooling system; • [Fig.5A]: a schematic view of an architecture of a first electrochemical test cell equipped with internal instruments for the thermal characterization of a reference electrochemical cell according to a first embodiment; • [Fig.5B]: a schematic view of an architecture of a second electrochemical test cell equipped with internal instruments for the thermal characterization of the reference electrochemical cell of [Fig.5A]; • [Fig. A]: a schematic view of the architecture of a first electrochemical test cell equipped with internal instruments for the thermal characterization of a reference electrochemical cell according to a second embodiment; • [Fig. 0B]: a schematic view of an architecture of a second electrochemical test cell equipped with internal instruments for the thermal characterization of the reference electrochemical cell of [Fig. 6A]; • [Fig. 7]: A schematic view of an electrochemical cell architecture test equipped with internal instruments for the thermal characterization of a reference electrochemical cell according to a third embodiment; • [Fig.8]: a schematic view of an architecture of an electrochemical test cell equipped with internal instruments for the thermal characterization of a reference electrochemical cell according to a fourth embodiment; • [Fig. 9]: a schematic view of a cell architecture electrochemical test equipped with internal instruments for the thermal characterization of a reference electrochemical cell according to a fifth embodiment; • [Fig. 10]: a schematic view of an architecture of an electrochemical test cell equipped with internal instruments for the thermal characterization of a reference electrochemical cell according to a sixth embodiment; • [Fig. 11]: a schematic exploded view of the different external faces of an electrochemical test cell equipped with external instruments.

[0043] For clarity, identical or similar elements are identified by identical reference symbols throughout the figures.

[0044] In the description and claims, to clarify the description and claims, the terminology longitudinal, transverse, and vertical shall be adopted without limitation, with reference to the X, Y, Z trihedron shown in the figures. Detailed description of an embodiment

[0045] With reference to Figures 1 and 2, an electrochemical cell 100 conventionally comprises a stack 13 of interconnected positive electrodes and a stack of interconnected negative electrodes separated by a separator, known as a "stack" in Anglo-Saxon terminology. The positive electrodes are connected to each other at a positive terminal, and the negative electrodes are connected to each other at a negative terminal. Each stack 13 defines an electrode stack.

[0046] The electrochemical cell 100 includes a cup 11 defining a housing or interior space 18 defining a housing adapted to receive the electrochemical stack(s) 13 through a passage opening 11', and a cover 12 cooperating with a rim of the passage opening 11' of the cup 11 to at least partially close the passage opening 11'. In this way, once the set of electrochemical cells 13 is integrated into the cup 11, a plate forming a lid 12 is welded to the cup 11 (generally by laser) to achieve the structural connection and sealing of the electrochemical cell 100 so as to close the case 10 thus formed, preferably made up of the cup 11 and the lid 12. The case thus forms a sealed envelope 10 inside which is housed one or more stack(s) 13 of positive and negative electrodes separated by a separator.

[0047] The bucket 11 comprises an electrically conductive body, preferably metallic, preferably also made of aluminium.

[0048] The manufacture of a cell conventionally involves a number of steps. The electrodes are first manufactured during an electrode manufacturing step. Once the electrodes are manufactured, they are assembled by stacking or stacking 13 of electrodes. Thus, the cathodes and anodes are stacked and separated by an insulating separator. For example, in the case of prismatic cells as illustrated in the figures, the electrode stacks 13 are produced by a known "Z"-folding process: the anode and cathode sheets are inserted alternately from one side and then the other into the Z-folded separator. This produces electrode stacks 13 of the type comprising a stack of positive and negative electrodes separated by a separator. The stack 13 is secured with adhesive tape.

[0049] The cells are then assembled. The electrode stacks 13 are soldered to connectors, generally made of copper or aluminum, and then to the cell cover 12. The soldered stacks 13 are then protected by an insulating sleeve and inserted into the prismatic housing. The cover 12 is then soldered around its entire periphery to the cup 11 to ensure a seal.

[0050] Once the 100 cells are assembled and operational, they are then assembled into modules and connected together to form a "battery pack", that is to say an association of several modules.

[0051] According to the invention, we are particularly interested in instrumented cells. In order to characterize a reference electrochemical cell, tests are carried out on instrumented electrochemical test cells 100 while measuring and recording measurements from a plurality of instruments equipping the electrochemical test cell 100 based on predetermined constraints applied to it.

[0052] According to the invention, a method for thermal characterization of a reference electrochemical cell of an electric battery includes an internal and external instrumentation step of at least one or more test electrochemical cell(s) 100, 101, 102 each having an architecture identical to an architecture of the reference electrochemical cell.

[0053] During this instrumentation step, each electrochemical test cell 100,101,102 is thus instrumented by a plurality of external instruments 20 equipping the envelope 10 of the associated electrochemical test cell, on the outside side 19 of the envelope 10 opposite to the inside space 18.

[0054] During this instrumentation step, each electrochemical test cell 100, 101, 102 is also instrumented by a plurality of internal instruments 30 housed in the internal space 18 of the associated casing 10 and configured to determine: • a vertical thermal gradient with respect to a vertical reference axis Z contained in a reference plane P parallel to the electrodes; and • if the number of stacks 13 is greater than or equal to two, a transverse thermal gradient with respect to a transverse reference axis Y perpendicular to the reference plane P; and / or • an average temperature.

[0055] In the illustrated embodiments, the internal instruments 3 0 include sensors, in particular thermocouples which are positioned inside the housing 10 of the cell and each connected from the outside by means of electrical links 35 including electrical cables.

[0056] The thermocouples forming internal instruments 30 are placed in the housing during the assembly of the associated cell 100.

[0057] A thermocouple 30 is a sensor used to measure temperature. It consists of two metals of different types joined at one end. When the junction of the metals is heated or cooled, a variable voltage is produced, which can then be converted into temperature. A resin is used to fix portions The ends of the thermocouple wires protrude from the outside of the housing 10, which forms an enclosure with associated connectors for linking them to an electrical circuit (not shown). The resin is configured to form a watertight barrier and prevent the migration of electrolyte or a gaseous compound between the wires and the thermocouple sheath. In practice, the electrical wires 35 of the thermocouples 30 exit the housing 10 to connect to a dedicated housing, the wires being housed in one or more sheaths. The resin on the distal end of the sheath connecting to the dedicated housing prevents the migration of electrolyte through the associated thermocouple by capillary action. A resin similar to, or even identical to, the resin of a sealing coating 15, which will be described later, should preferably be chosen. The electrical wires 35 of the thermocouples are preferably twisted in pairs to limit the upward movement of electrolyte by capillary action.

[0058] Each thermocouple 30 is connected to an electrical connection means 35, such as one or more electrical wires, for connecting it to a measuring unit, each comprising, for example, one or more electrical cables. The electrical connection means 35 of the internal thermocouples 30 are arranged so as to pass through the casing 10 of the associated electrochemical cell 100, 101, 102 in a sealed manner. Each of the electrical connection means 35 has a protective sheath configured to be resistant to an electrolyte of the associated electrochemical cell 100, 101, 102. In this embodiment, the thermocouples selected for the measurements are insulated with perfluoroalkoxy (PFA).

[0059] The housing 10 is provided with one or more through-holes 17 configured to be traversed by the electrical connection means 35 (see [Fig. 2]). Each of the through-holes 17 (here three in number) is sized so that at least one of the associated electrical cables can pass through it snugly, preferably a single cable from among the electrical cables of the instrumented cell 100. These holes 17 are located here on the cover 12 of the housing 10. The holes 17 are through-holes such that each one passes locally through the cover 12 along its thickness, that is, between its outer and inner faces. Each of the holes 17 has a cylindrical shape. In this embodiment, given the size of the electrical cables, each of the holes 17 has a diameter of 1 mm.

[0060] During the internal instrumentation step of the electrochemical test cell(s) 100, the said internal instruments 30 are installed on the electrode stacks 13 to obtain instrumented electrode stacks 13 and the electrical connection means 35, consisting here of electrical cables and connected to the internal instruments 30 through the cover 12, are also installed.

[0061] For the installation of the internal instruments 30, the sensors, including the thermocouples, are held on one edge of the electrode stacks 13 by means of adhesive tape compatible with the electrolyte, i.e., which is not degraded by contact with the electrolyte. The thermocouples of the internal instruments 30 are further configured so that each is compatible with an electrolyte of the associated electrochemical test cell 100, 101, 102.

[0062] The positioning areas of the internal instruments 30 are chosen to allow the validation of the most realistic digital twin possible, preferably areas within the cell that are subject to the greatest temperature gradients, and to minimize the risk of internal short circuits. The intervening regions between the different electrode stacks 13 are preferably free of instruments due to the risk of mechanical degradation of the electrodes or degradation of the thermocouple tips. Areas located on the edges of the electrode stacks 13 are therefore preferably chosen.

[0063] The location of the internal instruments 30 will be described in more detail later, with reference to Figures 5 to 10.

[0064] Regarding the installation of the electrical cables 21 connected to the internal instruments 30 through the cover 12, a step of inserting the electrical cables 35 through the through holes 17 in the cover 12 is implemented, followed by a step of hermetically sealing the holes 17 through which the electrical cables 35 pass by applying a sealing coating 15.

[0065] This sealing coating 15 is applied locally to the cover 12, on the side of an outer face of the cover opposite its inner face, said inner face being configured to be oriented towards the interior of the cell 100 in the instrumented position. The coating is located at the through-holes 17.

[0066] The sealing coating 15 comprises a sealing resin. In this example, the resin preferably comprises an epoxy resin compatible with an electrolyte composition, for example, an epoxy resin, and is configured to adhere locally to the surface of the cover, particularly a metallic one, to ensure the cover is sealed. The use of a resin at the through-holes 17 creates a resin plug that holds the electrical connections 35, particularly the electrical cables, in place and prevents electrolyte leakage through said holes 17.

[0067] In this example, the resin used is a 3M brand epoxy resin referenced “DP 100”.

[0068] According to another embodiment, the sealing coating 15 is silicone-based, preferably made of silicone.

[0069] According to one embodiment, the sealing coating 15 is made of epoxy material. The material forming the sealing coating 15 preferably has a hardness greater than or equal to 5 Shore D, preferably greater than or equal to 15 Shore D, and / or less than or equal to 95 Shore D, preferably less than or equal to 90 Shore D. Such hardness provides improved resistance to ensure sealing and withstand the stresses experienced. This type of sealing coating 15 is particularly advantageous because it has a hardness after polymerization suitable for use in a battery cell while having a viscosity before polymerization sufficient to migrate into gaps and small volumes. In the case of an epoxy resin, the sealing coating 15 preferably has a hardness between 80 and 85 Shore D.

[0070] Once the instrumented electrode stacks 13 and the electrical wires 35 passing through the cover 12 in a sealed manner thanks to the sealing coating 15, they are inserted inside the cup 11 of the housing 10 of the cell of the electrode stack or stacks 13 comprising at least the instrumented electrode stack or stacks inside a cup 11 of the housing 10 of the cell; then the cover 12 is fixed to the cup 11 to form the sealed housing 10 of the instrumented cell 100, in particular by laser welding as seen in [Fig.1].

[0071] As mentioned previously, each electrochemical test cell 100 is also instrumented by a plurality of external instruments 20 equipping the envelope 10 of the associated electrochemical test cell, on the outer side 19 of the envelope 10 opposite the inner space 18.

[0072] It should be noted that the external instruments 20 are positioned on the outer faces of the housing 10, which forms an envelope for both the cup 11 and the lid 12. This step of attaching the external instruments 20 can be carried out either after the associated electrochemical cell 100 has been assembled, or before. The advantage of instrumenting the outer faces of the housing with the external instruments 20, 21, 22, 23, 24, 25, 26, 27, 28 before the associated electrochemical cell 100 is assembled allows this step to be carried out concurrently with other assembly steps.

[0073] In the illustrated embodiments, the external instruments 20 comprise sensors, in particular thermocouples, which are positioned outside the cell housing 10 and connected externally by electrical linkages 35 comprising electrical cables. The external thermocouples 20 are similar to the internal thermocouples 30.

[0074] The location of the external instruments 20 on the housing 10 will be described in more detail later, with reference to [Fig.1 1].

[0075] Once the test cell(s) 100 have been assembled and instrumented, each one is positioned on a test device 200 schematically illustrated on [Fig. 3]. Thanks to such a test device 200, the characterization method can, on the one hand, implement a step of applying a predetermined stress profile to the instrumented test cell(s) 100, and on the other hand, measure and record the measurements from the internal instrument 30 and external instrument 20 during the step of applying the predetermined stress profile. It is thus possible to determine, in a relevant manner, at least the vertical and transverse thermal gradients and the associated average temperature.

[0076] The test device 200 comprises a support 201 on which an instrumented test cell 100 is mounted, and two lateral compression plates 202 between which the instrumented test cell 100 is placed for testing. The compression plates 202 are positioned vertically and longitudinally, i.e., parallel to the longitudinal reference axis X. In this way, the pressure exerted against the cell 100 is applied at its large lateral faces, i.e., the large faces of the cup 11 of the housing 10 of the test cell 100.

[0077] The support 201 is equipped with a cooling system and includes a support plate inside which flows a cooling line 201' configured to carry a coolant. In the illustrated example, the cooling was generated by a monoethylene glycol-type fluid diluted with 50% water circulating in the cooling line 201' through the cooling plate. The cooling is provided by the cooling system, which is itself controlled according to the temperature of the cell 100.

[0078] In the test position of the instrumented cell 100 to be tested positioned on the test device 200, said cell 100 is compressed between the two compression plates.

[0079] It should be noted that in this test position in the test device 200, a sheet of thermal insulation 203 is placed between, preferably interposed between, each of the two lateral compression plates 202 and the cell 100. These sheets of thermal insulation 203 can constitute a covering applied to each of the lateral compression plates 202. Furthermore, also in this test position in the test device 200, a thermal cushion 204 is placed between, preferably interposed between, the support 201 of the test device 200 and the cell 100.

[0080] The cell is electrically connected to a control unit configured to apply a predetermined stress profile to the associated test cell.

[0081] Applying a predetermined stress profile to the instrumented test cell(s) 100 preferably includes subjecting the instrumented test cell(s) 100 to a rapid load loading. For the purposes of the test, an example of a predetermined stress profile applied to the instrumented test cell(s) 100 is, for example, a rapid load loading at IC with an active cooling system, for example set at 25°C.

[0082] As a reminder, the capacity of a battery corresponds to its nominal value in ampere-hours (Ah) and describes the duration for which a battery can supply a certain current (A). For example, a 100 Ah battery can supply 100 amps to a system for 1 hour. The C-rate here designates a measure of the battery's nominal capacity. For example, a battery designed to discharge its total capacity (Ah) in 1 hour would be rated at 1 C, or in 2 hours would be rated at 0.5 C. More generally, the C-rate designates the charge or discharge rate, which is correlated with the lithiation or delithiation rate of the electrode material: C represents the capacity of a battery, generally measured in ampere-hours (Ah), indicating the amount of active material in the battery available for discharge.

[0083] During the step of applying the predetermined stress profile to the instrumented test cell(s) 100, a measurement and recording step of the measurements from the instruments during the application of the predetermined stress profile is implemented concurrently by a measuring unit (not shown) so as to determine at least the vertical and transverse thermal gradients and the associated average temperature. In other words, the overall temperature evolution of all the internal sensors 30 and external sensors 20 is measured as a function of time.

[0084] Fig. 4 illustrates a given state of the cell temperature at a given instant of a three-dimensional thermal simulation of a prismatic cell 100 subjected to such a rapid load stress, with an active cooling system equipping the test device 200 to cool the support on which the instrumented test cell(s) 100 rests during the tests.

[0085] Figure 4 specifically highlights the thermal behavior of such an instrumented test cell 100 during a test. Vertical and horizontal gradients are particularly evident: • vertically where the temperature decreases, along a vertical axis parallel to the vertical reference axis Z, from a zone Z12 near the lid 12 to a zone Z11 of the cup 11, and • horizontally, in particular transversely with respect to the bucket 11 where the temperature decreases, along a transverse axis parallel to the reference transverse axis Y, from a center of the Zll zone of the bucket 11 towards the sides of the housing 10.

[0086] Thus, and as shown by the simulation ([Fig. 4]), internal thermal gradients are present in the volume region of the stack, which are masked by the insulating base (thermal pad 204) of cell 100 and the aluminum casing 10. In active cooling scenarios, significant vertical or horizontal thermal gradients can lead to heterogeneous current densities, which limits performance and, ultimately, cell aging. Knowing the internal thermal behavior of cells during energy demand and within the framework of thermal management, better optimization could be applied to several cell health states.

[0087] As previously described, one of the objectives of the present invention is to be able to characterize as best as possible a given reference electrochemical cell 100, in order to improve its simulation and simulating its reaction in the way closest to reality.

[0088] For this reason, the various instruments, internal 30 as well as external 20, are positioned in a very precise way as illustrated in figures 5 to 11.

[0089] First, in order to avoid any disturbance of the measurements or any degradation of the electrochemical cell 100, only three thermocouples are used for each configuration.

[0090] Based on a number of criteria, such as the number of batteries 13, the position of a safety vent 14 of the cover 12, the location of each thermocouple was chosen to measure the temperature evolution during the customer profile.

[0091] Figures 5A, 5B and 6A, 6B illustrate configurations in which the reference electrochemical cell to be characterized comprises strictly more than two stacks 13 of electrodes, the instrumentation step comprises the internal and external instrumentation of two electrochemical test cells 100, 101, 102: - a first electrochemical test cell 101 among the two instrumented electrochemical test cells 101,102 comprising internal instruments 30 configured to determine the vertical and transverse thermal gradients; and - a second electrochemical test cell 102 among the two instrumented electrochemical test cells 101,102 comprising internal instruments 30 configured to determine the vertical thermal gradient and the average temperature.

[0092] With reference to Figures 5A and 5B, [Fig.5A] illustrates a schematic view of an architecture of a first electrochemical test cell 101 equipped with internal instruments 30 for the thermal characterization of a reference electrochemical cell, [Fig.5B] illustrating a schematic view of an architecture of a second electrochemical test cell 102 equipped with internal instruments 30 for the thermal characterization of this same reference electrochemical cell.

[0093] In particular, the first electrochemical test cell 101 of the two instrumented electrochemical test cells 101,102 comprises (see [Fig.5A]): - a first internal instrument 31 positioned in an area close to a lower edge of a first stack 13 of electrodes; - a second internal instrument 32 positioned in an area near an upper edge of the first stack 13 of electrodes, opposite the lower edge; and - a fourth internal instrument 34 positioned in an area near an upper edge of a second stack 13 of electrodes, preferably adjacent to the first stack 13 of electrodes;

[0094] In addition, the second electrochemical test cell 102 of the two instrumented electrochemical test cells 101,102 comprises (see [Fig.5B]): • a first internal instrument 31 positioned in an area close to a lower edge of a first stack 13 of electrodes; • a second internal instrument 32 positioned in an area near an upper edge of the first stack 13 of electrodes, opposite the lower edge; and • a third internal instrument 33 positioned in an area near a lateral edge of the first stack 13 of electrodes.

[0095] In this configuration, the thermal characterization of a reference electrochemical cell for an electric battery is obtained from tests conducted on two test electrochemical cells 101, 102, each having an architecture identical to that of the reference electrochemical cell. These two cells can be tested on the same test device 200 or on separate test devices 200. In this case, the tests are preferably conducted such that each of the two test cells 101, 102 is electrically connected to the same control unit configured to apply a predetermined stress profile to the associated test cell simultaneously.

[0096] The first internal instrument 31 is positioned on the lower edge of the first stack 13 of electrodes, in particular in the middle of the lower edge, equidistant from the vertical edges longitudinally delimiting the associated stack 13 of electrodes.

[0097] In such a configuration, for each of the first and second electrochemical cells 101, 102, the first and second internal instruments 31, 32 are positioned at two different vertical levels and placed on the same first stack 13 of electrodes. It is therefore possible to determine a vertical temperature gradient using this pair of thermocouples 30.

[0098] With regard to the first electrochemical test cell 101, the second and fourth internal instruments 32, 34 are positioned at the same vertical level and placed on separate adjacent stacks 13 of electrodes. It is therefore possible to determine a horizontal, in particular transverse, temperature gradient using this pair of thermocouples 30.

[0099] The second and fourth internal instruments 32, 34 are each positioned on the upper edge of two separate adjacent stacks 13 of electrodes and positioned such that the second and fourth internal instruments 32, 34 are transversely adjacent. In other words, the distance separating the second internal instrument 32 from a vertical edge on one longitudinal side of the associated stack 13 of electrodes is equal to the distance separating the fourth internal instrument 34 from the vertical edge on the same longitudinal side of the corresponding stack 13 of electrodes.

[0100] It will be noted that the longitudinal position of the second internal instrument 32 of the first electrochemical test cell 101 and of the fourth internal instrument 34 of the second electrochemical cell 102 on the upper edge of the associated electrode stack 13 is determined so as to be placed in an area close to a safety vent 14 of the cover 12. Such a safety vent 14 allows degassing of the electrochemical cell in the event of internal pressure exceeding a threshold pressure.

[0101] With regard to the second electrochemical test cell 102, the third internal instrument 33 is positioned on the lateral edge of the first stack 13 of electrodes, at mid-height, vertically, of said stack, that is to say a position substantially equidistant from the lower edge and the upper edge of the associated stack 13, namely here the first stack 13. This position was determined following tests so as to be representative at an average temperature observed inside the housing 10.

[0102] In the embodiment illustrated in Figures 5A and 5B, each of the first and second electrochemical cells 101, 102 comprises at least three stacks or arrangements 13 of electrodes, in particular four here. The first arrangement 13 of each of these first and second instrumented electrochemical test cells 101, 102 is chosen so as to be adjacent to an associated parallel wall of the housing 10 of the corresponding cell 101, 102. For a given cell, the first arrangement 13 is therefore located between a wall of the housing 10 and the second arrangement 13 of electrodes, itself adjacent to the first arrangement 13.

[0103] The second embodiment illustrated in Figures 6A and 6B differs from the first embodiment of Figures 5A and 5B essentially in that the safety vent 14 is located in a central area of ​​the cover and not offset on a longitudinal end portion of the cover 12. The longitudinal position of the second internal instrument 32 of the first electrochemical test cell 101 and of the fourth internal instrument 34 of the second electrochemical cell 102 on the upper edge of the associated electrode stack 13 is modified accordingly so that the associated thermocouples 32, 34 are placed longitudinally in the center of the upper edge of the associated electrode stack 13, and therefore in the vicinity of the safety vent 14 of the cover 12.

[0104] Fig. 7 illustrates a third embodiment in which the reference electrochemical cell to be characterized comprises exactly two stacks 13 of electrodes.

[0105] In such a configuration, the instrumentation step comprises the internal and external instrumentation of a single electrochemical test cell 100 in which the internal instruments are configured to determine: - on the one hand, the vertical thermal gradient and: - on the other hand the transverse thermal gradient.

[0106] Tests have made it possible, in particular, to reliably extrapolate an average internal temperature of the cell during the tests from the thermocouples already positioned inside the instrumented test cell 100. The aim is to find a compromise that simplifies the characterization method with a single instrumented test cell 100 without reducing the quality of the results obtained, or only to a negligible extent.

[0107] As regards the positioning of the internal instruments in this third embodiment, they are similar to those of the first cell 101 for the first embodiment.

[0108] In particular, the instrumented electrochemical test cell 100 comprises (see [Fig.7]): - a first internal instrument 31 positioned in an area close to a lower edge of a first stack 13 of electrodes; - a second internal instrument 32 positioned in an area near an upper edge of the first stack 13 of electrodes, opposite the lower edge; and - a fourth internal instrument 34 positioned in an area near an upper edge of a second stack 13 of electrodes, preferably adjacent to the first stack 13 of electrodes;

[0109] The first and second internal instruments 31, 32 are positioned at two different vertical levels and placed on the same first stack 13 of electrodes. It is therefore possible to determine a vertical temperature gradient using this pair of thermocouples 30. Furthermore, the second and fourth internal instruments 32, 34 are positioned at the same vertical level and placed on separate, adjacent stacks 13 of electrodes. It is therefore possible to determine a horizontal, in particular transverse, temperature gradient using this pair of thermocouples 30.

[0110] Figure 8 illustrates a fourth embodiment in which the reference electrochemical cell to be characterized comprises exactly two stacks 13 of electrodes. The fourth embodiment of Figure 8 differs from the third embodiment of [Fig.7] essentially in that the safety vent 14 is located in a central area of ​​the cover and not offset on a longitudinal end portion of the cover 12. This is the same distinction as between figures 5 and 6.

[0111] Fig. 9 illustrates a fifth embodiment in which the reference electrochemical cell to be characterized comprises a single stack of electrodes.

[0112] In such a configuration, the instrumentation step comprises the internal and external instrumentation of a single electrochemical test cell 100 in which the internal instruments are configured to determine: - on the one hand, the vertical thermal gradient and: - on the other hand, the average temperature.

[0113] Indeed, in such a configuration, it is not possible to measure a transverse temperature gradient from stacks 13 of separate electrodes.

[0114] As regards the positioning of the internal instruments in this fifth embodiment, they are similar to those of the second cell 102 for the first embodiment.

[0115] In particular, the instrumented electrochemical test cell 100 comprises (see [Fig.9]): • a first internal instrument 31 positioned in an area near a lower edge of a first and only stack 13 of electrodes; • a second internal instrument 32 positioned in an area near an upper edge of the first and only stack 13 of electrodes, opposite the lower edge; and • a third internal instrument 33 positioned in an area near a lateral edge of the first and only stack 13 of electrodes.

[0116] In such a configuration, the first and second internal instruments 31, 32 are positioned at two different vertical levels and placed on the same first stack 13 of electrodes. It is therefore possible to determine a vertical temperature gradient using this pair of thermocouples 30.

[0117] The third internal instrument 33 is positioned on the lateral edge of the first stack 13 of electrodes, at mid-height, vertically, of said stack, that is to say a position substantially equidistant from the lower edge and the upper edge of the associated stack 13, namely here the first stack 13.

[0118] Figure 10 illustrates a sixth embodiment in which the reference electrochemical cell to be characterized comprises exactly one stack 13 of electrodes. The sixth embodiment of Figure 10 differs from the fifth embodiment of Figure 9 essentially in that the safety vent 14 is located in a central area of ​​the lid and not offset on a longitudinal end portion of the lid 12. This is the same distinction as between figures 5 and 6 or between figures 7 and 8.

[0119] Figure 11 illustrates a schematic view of the various external faces of an electrochemical test cell 100 equipped with external instruments. Regardless of the embodiments of the internal instruments 30 described above, the instrumented test cell, in addition to the three internal instruments housed in its internal space 18, is instrumented on the external side as illustrated in Figure 11.

[0120] Thus, each instrumented electrochemical test cell 100,101,102 is equipped with at least eight, in particular here exactly eight, external instruments.

[0121] Furthermore, for a given instrumented electrochemical test cell 100, 101, 102, the instruments are arranged as follows: - an external instrument 21, unique here, is positioned on the cover 12 of the housing 10 of the associated electrochemical test cell 100,101,102, in particular in the center of the cover 12; - an external instrument 27, unique here, is positioned on a bottom of the cup 11 of the housing 10 of the associated electrochemical test cell 100,101,102, in particular in the center of the bottom of the cup 11 of the housing 10; - Five external instruments 22, 23, 24, 25, 26 are positioned on one of the large faces of the cup 11 of the housing 10 of the associated electrochemical test cell 100, 101, 102, the large faces being parallel to the vertical and longitudinal reference plane. For these external instruments 22, 23, 24, 25, 26, the associated instrumented large face is chosen from among the two large faces so as to correspond to the large face that is adjacent to the first instrumented stack 13; and - an external instrument 28, unique here, is positioned on a small face of the cup of the associated electrochemical test cell 100, 101, 102, the small face being perpendicular to the reference plane P, the small face being chosen, if necessary, from among the two small faces longitudinally delimiting the housing 10 so as to correspond to the small face closest to the safety vent 14 of the cover 12. The external instrument 28 is positioned vertically at mid-height of the corresponding small face, that is to say, a position substantially equidistant from the cover 12 and the bottom of the cup 11, and horizontally so as to be aligned longitudinally with the reference plane P of the - namely here the first stack 13. This position was determined following tests so as to be representative at an average temperature observed inside the case 10.

[0122] Among the external instruments 22, 23, 24, 25, 26 positioned on the large face of the cup 11 of the associated electrochemical test cell 100, 101, 102, three lateral external instruments 22, 23, 24 are positioned so as to be aligned vertically along the large instrumented face and being centered longitudinally with respect to the large instrumented face, these three lateral external instruments 22, 23, 24 comprising an upper lateral instrument 22 near the lid, a vertically centered middle lateral instrument 23 and a lower lateral instrument 24 near the bottom of the cup 11.

[0123] In addition here, two lateral external instruments 25, 26 are positioned so as to be aligned vertically along the large instrumented face and to be offset longitudinally in the vicinity of the small face of the housing 10 instrumented by the external instrument 28. These two lateral external instruments 25, 26 comprise an upper offset lateral instrument 25 near the cover 12 and a median offset lateral instrument 26 located vertically at mid-height.

[0124] Tests at the cell level provide information on temperature gradients at the stack 13 level as well as between the external temperature and the internal temperature at the same location.

[0125] Indeed, it should be noted that: • the first internal instrument 31 and the external sensors 24 and 27 are located in the same lower region; • the second and fourth internal instruments 32 and the external sensors 22 or 25, or even 21, are found in the same upper region depending on the position of the vent 14; • the third internal instrument 33 and the external sensors 26 and 28 are located in the same lateral region.

[0126] It is understood from the above description that the advantages of the present invention are substantial, among which the following may be mentioned: - enable thermal validation of digital and physical products, by reducing the electrical validation test plan with correlated simulations; - to allow evaluation of the vertical thermal gradient during relevant mission profiles; - to enable the development of performance optimization strategies such as BSM mapping for fast charging and regeneration; - to allow the development of reduced thermal models to enrich an internal functional library of the BMS; - to allow analysis of the efficiency of a cooling system; - to allow for a better understanding of the aspects related to product safety, to improve the characterizations of thermal runaway, and thus to better avoid them by adapting the BMS accordingly and developing cells that limit this risk; - to allow testing on materials compatible with the composition of a predetermined electrolyte.

[0127] Naturally, the invention is described above by way of example. It is understood that a person skilled in the art is able to carry out different embodiments of the invention without departing from the scope of the invention.

[0128] It is emphasized that all features, as they are apparent to a person skilled in the art from the present description, drawings and attached claims, even if in practice they have only been described in relation to other specific features, both individually and in any combinations, can be combined with other features or groups of features disclosed herein, provided that this has not been expressly excluded or that technical circumstances make such combinations impossible or meaningless.

Claims

Demands

1. Method for thermal characterization of a reference electrochemical cell of an electric battery of the type comprising an envelope (10) within which is housed at least one stack (13) of positive and negative electrodes separated by a separator, the characterization method comprising: - an internal and external instrumentation step of at least one or more electrochemical test cell(s) (100, 101, 102) having an architecture identical to an architecture of the reference electrochemical cell, each being instrumented by: • a plurality of external instruments (20, 21, 22, 23, 24, 25, 26, 27, 28) equipping the envelope (10) of the associated electrochemical test cell, on the outside (19) of the envelope (10) opposite the inside space;and • a plurality of internal instruments (30, 31, 32, 33, 34) housed in the internal space (18) of the associated envelope (10) configured so as to determine a vertical thermal gradient with respect to a vertical reference axis (Z) contained in a reference plane (P) parallel to the electrodes and, if the number of stacks (13) is greater than or equal to two, a transverse thermal gradient with respect to a transverse reference axis (Y) perpendicular to the reference plane (P) and / or an average temperature; - a step of placing the instrumented test cell(s) (100, 101, 102) on a test device (200); - a step of applying a predetermined stress profile to the instrumented test cell(s) (100, 101, 102);- a step of measuring and recording the measurements from the instruments during the step of applying the predetermined stress profile, so as to determine at least the vertical and transverse thermal gradients and the associated average temperature.

2. A thermal characterization method according to claim 1, characterized in that the reference electrochemical cell to be characterized comprises more than two stacks (13) of electrodes,

3.

4.

5. The instrumentation stage includes the internal and external instrumentation of two electrochemical test cells (100, 101, 102): - a first electrochemical test cell (101) among the two instrumented electrochemical test cells (101, 102) comprising internal instruments (30) configured to determine the vertical and transverse thermal gradients; and - a second electrochemical test cell (102) among the two instrumented electrochemical test cells (101, 102) comprising internal instruments (30) configured to determine the vertical thermal gradient and the average temperature. A thermal characterization method according to claim 1, characterized in that the reference electrochemical cell to be characterized comprises only one or two stacks (13) of electrodes, the instrumentation step comprises the internal and external instrumentation of a single electrochemical test cell (100) in which the internal instruments are configured to determine the vertical thermal gradient and: - the average temperature, if the reference electrochemical cell to be characterized comprises only a stack (13) of electrodes; or - the transverse thermal gradient, if the reference electrochemical cell to be characterized comprises only two stacks (13) of electrodes Thermal characterization method according to any one of claims 1 to 3, characterized in that each instrumented test cell (100, 101, 102) is equipped with at least three, preferably exactly three, internal instruments (30). Thermal characterization method according to claims 2 and 4, characterized in that: - the first electrochemical test cell (101) among the two instrumented electrochemical test cells (101, 102) comprises a first internal instrument (31) positioned in an area near a lower edge of a first stack (13) of electrodes, a second internal instrument (32) positioned in an area near an upper edge of the first stack (13) of electrodes, opposite the lower edge, and a fourth internal instrument (34) positioned in an area near an upper edge of a second stack (13) of electrodes, preferably adjacent to the first stack (13) of electrodes;- the second electrochemical test cell (102) among the two instrumented electrochemical test cells (101, 102) comprises a first internal instrument (31) positioned in an area near a lower edge of a first stack (13) of electrodes, a second internal instrument (32) positioned in an area near an upper edge of the first stack (13) of electrodes, opposite the lower edge, and a third internal instrument (33) positioned in an area near a lateral edge of the first stack (13) of electrodes.;

6. Thermal characterization method according to the preceding claim, characterized in that the first stacks (13) of the first and second instrumented electrochemical test cells (101, 102) are stacks adjacent to an associated parallel wall of the corresponding envelope (10).

7. Thermal characterization method according to any one of the preceding claims, characterized in that the envelope (10) of the instrumented electrochemical test cell (100, 101, 102) comprises a prismatic housing (10), the housing (10) comprising a cup (11) having an opening closed by a lid (12).

8. A thermal characterization method according to claim 7, dependent at least on claim 5, characterized in that the second and fourth internal instruments (32, 34) of the first electrochemical test cell (101) and the second instrument internal (32) of the second electrochemical test cell (102) are located in an area close to a safety vent (14) in the cover (12) configured to allow degassing of the electrochemical cell in the event of internal pressure exceeding a threshold pressure.

9. A thermal characterization method according to any one of the preceding claims, characterized in that each instrumented electrochemical test cell (100, 101, 102) is equipped with at least eight, preferably exactly eight, external instruments.

10. A thermal characterization method according to the preceding claim depending at least on claims 7 and 5, characterized in that, for a given instrumented electrochemical test cell (100, 101, 102): - at least one of the external instruments (20, 21, 22, 23, 24, 25, 26, 27, 28), preferably a single external instrument (21), is positioned on the lid (12) of the associated electrochemical test cell (100, 101, 102); - at least one of the external instruments (20, 21, 22, 23, 24, 25, 26, 27, 28), preferably a single external instrument (27), is positioned on a bottom of the cup of the associated electrochemical test cell (100, 101, 102);- a plurality of external instruments (22, 23, 24, 25, 26), preferably at least five external instruments, preferably exactly five external instruments, are positioned on a large face of the associated electrochemical test cell cup (100, 101, 102), the large face being parallel to the reference plane; and - at least one of the external instruments (20, 21, 22, 23, 24, 25, 26, 27, 28), preferably a single external instrument (28), is positioned on a small face of the associated electrochemical test cell cup (100, 101, 102), the small face being perpendicular to the reference plane (P).

11. A thermal characterization method according to the preceding claim, dependent at least on claim 6, characterized in that the external instruments (22, 23, 24, 25, 26) positioned on the large face of the cup (11) of the electrochemical cell (100, 101, 102) associated test are positioned on this single large face among the large faces of the associated cell cup, the large instrumented face corresponding to the large face adjacent to the first stack (13) of the first or second corresponding electrochemical cell (101, 102).

12. Thermal characterization method according to the preceding claim, characterized in that among the external instruments (22, 23, 24, 25, 26) positioned on the large face of the cup (11) of the associated electrochemical test cell (100, 101, 102): - three lateral external instruments (22, 23, 24) are positioned so as to be aligned vertically along the large instrumented face and being longitudinally centered with respect to the large instrumented face, these three lateral external instruments (22, 23, 24) comprising an upper lateral instrument (22) near the lid, a vertically centered middle lateral instrument (23) and a lower lateral instrument (24) near the bottom of the cup (11);and / or - two external lateral instruments (25, 26) are positioned so as to be vertically aligned along the large instrumented face and being longitudinally offset, these two external lateral instruments (25, 26) comprising an upper offset lateral instrument (25) near the cover (12), a median offset lateral instrument (26).;

13. A thermal characterization method according to any one of the preceding claims, depending at least on claims 10 and 8, characterized in that the small face of the cup (11) of the electrochemical cell (100, 101, 102) on which the external instrument (28) is positioned corresponds to a face perpendicular to the lid (12) and to the bottom (11) of the cup (10), the small face being chosen from among the small face closest to the safety vent (14) of the lid (12) configured to allow degassing of the associated electrochemical cell in the event of internal pressure exceeding a threshold pressure.

14. A thermal characterization method according to any one of the preceding claims, characterized in that the

15.

16. instruments include sensors, preferably temperature sensors, and even more preferably thermocouples. Thermal characterization method according to the preceding claim, characterized in that the thermocouples of the internal instruments (30, 31, 32, 33, 34) at least are configured so that each is compatible with an electrolyte of the associated electrochemical test cell (100, 101, 102). Thermal characterization method according to claims 14 and 15, characterized in that each thermocouple (31, 32, 33, 34) is connected to an electrical linkage (35) for linking it to a unit of measurement, comprising for example each one or more electrical cable(s), the electrical linkage means (35) of the internal thermocouples (31, 32, 33, 34) being arranged so as to pass through in a sealed manner the envelope (10) of the associated electrochemical cell (100, 101, 102), each of the electrical linkage means (35) having at least one protective sheath configured to be resistant to an electrolyte of the associated electrochemical cell (100, 101, 102).

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