DEVICE FOR MAPPING THE DISTRIBUTION OF POTENTIAL IN AN ELECTROCHEMICAL CELL

Abstract

An electrochemical cell (1) acting as a Potential Electrochemical Microscope (PEM) comprises a working electrode (2) and a counter electrode (3), a solid electrolyte (4), at least one sensor (5) of a characteristic cell quantity, at least two current collectors, at least one potential collector (6), and a support holding the working electrode (2), the counter electrode (3), the electrolyte (4), the sensor (5), and the current collectors (6). The device is parallelepiped-shaped, cylindrical, spherical, hemispherical, or conical, and includes a lower support, an upper support, and a gasket separating the lower and upper supports. The lower support includes at least five compartments for storing electrochemical cell elements (1). Figure for the abstract: Fig 1

Description

Title of the invention: DEVICE FOR MAPPING POTENTIAL DISTRIBUTION IN AN ELECTROCHEMICAL CELL technical field

[0001] The present invention relates to the field of electrochemical cells including electric batteries, and particularly the mapping of an electrochemical cell according to different variables, and in particular the potential distribution and by extension the current through the circuit.

[0002] The challenges of energy transition and independence from fossil fuels have led to the need for the electrification of transport vehicles. The major drawback of electric vehicles is their energy range. Indeed, this range is lower than that of internal combustion engine vehicles, and to compensate for this deficit, it is necessary to design batteries with a higher energy density than existing ones.

[0003] In addition, there is the problem of battery aging. An electric battery is composed of a set of electrochemical cells connected in series and / or parallel. An electrochemical cell essentially comprises a working electrode and a counter electrode, each made of electrically conductive materials, and at a minimum, an electrolyte separating the two electrodes to ensure ion transport. More specifically, a solid electrolyte prevents a short circuit between the electrodes by inhibiting dendritic growth.

[0004] The problems of battery autonomy and aging have led to the question of the economic viability of the electric vehicle.

[0005] The choice of materials used to make up batteries is therefore an important step in addressing the problems mentioned. In order to select suitable materials, it is essential to determine the chemical properties of the chosen materials and, above all, their electrochemical properties.

[0006] The chemical stability of the cell components is studied by chemical speciation methods such as the nuclear magnetic resonance (NMR) method or the infrared (IR) method.

[0007] The differential scanning calorimetry (DSC) method is used to study the thermal stability of cell components.

[0008] As for the electrochemical properties, they are studied by galvanostatic or potentiostatic polarization methods. The electrochemical properties result from the distribution of the electrochemical potential or from the distribution of the ionic current in the cell. Electrochemical potential or ionic current profiles allow us to understand ion transport phenomena. One solution is therefore to propose a device capable of measuring the cell potential during battery operation in order to access the electrochemical properties of the electrolytes.

[0009] During the charging or discharging of an electrochemical cell, oxidation and reduction reactions occur at the electrodes. These phenomena create a concentration gradient and therefore a potential gradient within the cell. Thus, analyzing the potential or concentration distribution makes it possible to determine the actual performance of the cell.

[0010] However, during electrochemical characterization, the electrodes can undergo secondary reactions. Consequently, the voltage or current measured across the cell is subject to errors and does not allow for an effective determination of battery performance. Therefore, to overcome this obstacle and improve the accuracy of potential measurements, additional reference electrodes are introduced into the cell, used as potential sensors. The performance of the electrolyte in the cell can thus be evaluated, among other things, by measuring the voltage between the sensors.

[0011] An electrochemical cell generally comprises a support that holds each cell component in specific compartments. The supports currently available are cylindrical and have at most four electrodes: an anode electrode, a cathode electrode, a reference electrode in the anolyte, and a reference electrode in the catholyte. However, the cylindrical geometry of the support promotes convection phenomena during electrochemical characterization. Furthermore, these cylindrical supports are more suitable for liquid electrolytes because the weight of solid electrolytes can generate an additional force in the balance of forces influencing the mobility of ionic species in solution. Characterizing solid electrolytes with greater precision requires the development of new measurement tools.

[0012] The document "Method of the Four-Electrode Electrochemical Cell for the Characterization of Concentrated Binary Electrolytes: Theory and Application" is known, in particular, and describes a multi-electrode cell support model with four electrodes: an anode electrode, a cathode electrode, a reference electrode in the anolyte, and a reference electrode in the catholyte. This model allows for the characterization of a liquid electrolyte, as the support is cylindrical. However, these four electrodes do not allow for direct mapping of the potential distribution, and the results may exhibit distorted shapes. Furthermore, the effect of convection due to the The cylindrical shape of the support causes potential distortions that must be taken into account. Description of the invention

[0013] The invention relates to an electrochemical cell comprising:

[0014] - a working electrode and a counter electrode,

[0015] - a solid or viscous liquid electrolyte,

[0016] - at least one sensor of a characteristic quantity of the cell,

[0017] - at least two current and / or cell voltage collectors,

[0018] - at least one potential collector,

[0019] - a support holding the working electrode, the counter electrode, the electrolyte, the sensor, and current and potential collectors.

[0020] The device may be parallelepiped, cylindrical, spherical, hemispherical, or conical, depending on the required specifications. The device comprises a lower support, an upper support, and at a minimum, a sealing gasket separating the lower and upper supports. The lower support includes at least five compartments for storing electrochemical cell elements. The number of sensors in the cell may be increased depending on the cell dimensions.

[0021] Advantageously, the lower support comprises a central compartment containing the electrolyte and the sensor, a compartment containing the working electrode and a compartment containing the counter electrode both positioned at the ends of the central compartment, and two compartments containing two of the current collectors, positioned at the ends of the lower support.

[0022] The electrodes and the sensor are sheets of lithium (Li-ion) or sodium (Na-ion), or other metal ions (Aluminum Al, magnesium Mg, Zinc Zn, and in general any electronegative metal) used in metal-ion batteries. The geometry of the electrodes can be rectangular, cylindrical, or any geometry related to a 3D material.

[0023] The sensor is a potential sensor.

[0024] According to one embodiment, the current and potential collectors are copper or even aluminum foils. Copper rods or other metal geometries could also be suitable. The potential collector is a copper wire comprising insulation made of polytetrafluoroethylene (PTFE) and / or polyvinyl chloride (PVC).

[0025] Optionally, the electrolyte comprises polymer, co-polymer, composites, or gel, used as solvents and one or more solutes.

[0026] According to one embodiment, the device is machined using polyetheetherketone (PEEK) and / or polytetrafluoroethylene (PTFE), but other polymers could be suitable.

[0027] Advantageously, the central compartment of the lower support has at least one groove containing the sensor. The number of grooves can be increased at will, each groove accommodating a sensor. In addition to this parallelepiped geometry, cylindrical, spherical, or conical geometries can be used.

[0028] Optionally, the current collectors are suitable for being connected to a potentiostat, an external generator of any type, and / or a multimeter (or any type of measuring device) in order to measure the characteristic quantity of the electrochemical cell.

[0029] The invention also relates to a battery comprising a set of electrochemical cells as defined above.

[0030] The invention further relates to a method for assembling an electrochemical cell comprising a working electrode and a counter electrode, a solid electrolyte, at least one sensor for a characteristic quantity of the cell, at least two current collectors, at least one potential collector, and a device supporting the working electrode, the counter electrode, the electrolyte, the sensor, and the current and potential collectors. The device may be parallelepiped-shaped, cylindrical, spherical, hemispherical, or conical.The device comprises, at a minimum, a lower support, an upper support and a sealing gasket separating the lower support and the upper support, and the lower support comprises a central compartment containing the electrolyte and the sensor, a compartment containing the working electrode and a compartment containing the counter electrode both positioned at the ends of the central compartment, and two compartments containing two of the current collectors, positioned at the ends of the lower support.

[0031] The method for assembling an electrochemical cell comprises at least the following steps: - sensor preparation; - positioning of the sensor in the central compartment, the central compartment having at least one groove suitable for receiving the sensor; - positioning of the electrolyte in the central compartment; - positioning of the working electrode and the counter electrode in their respective compartments; - placement of the sealing gasket over the lower support; - positioning of the current collectors in their respective compartments; - fixing the upper support onto the entire lower support and the sealing gasket; - insertion of the electrochemical cell into an airtight and watertight bag and sealing of said airtight bag. Brief description of the drawings

[0032] Other objects, 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:

[0033] - Fig. 1 is a schematic top view of an electrochemical cell;

[0034] - The [Fig.2] is a schematic view of the support of an electrochemical cell;

[0035] - Figure 3 is a schematic top view of the lower support of a cell electrochemical;

[0036] - Figure 4 is a schematic view of the lower support of a cell electrochemical;

[0037] - Figure 5 is a schematic view of an electrochemical cell connected to a potentiostat and a multimeter, allowing the application of a potential, or a current, or the monitoring of the cell's potential;

[0038] - Fig. 6 is a schematic view representing the principle of voltage measurement in an electrochemical cell;

[0039] - Figure 7 is a graph representing the current and voltage of a cell electrochemical function of time; and

[0040] - Figure 8 is a graph representing the temporal evolution of the tensions of a electrochemical cell, during various current draws and using a specific electrolyte. Detailed description

[0041] An electrochemical cell 1 comprises a working electrode 2, a counter electrode 3, a solid or viscous liquid electrolyte 4 separating the working electrode 2 and the counter electrode 3, at least one sensor 5 of a characteristic quantity of the cell, for example the potential at a given position in the electrolyte, at least two current collectors 6, at least one potential collector 6 and a device 7 for holding the components of the cell 1. The electrochemical cell acts as a Potential Electrochemical Microscope (PEM).

[0042] The working electrode 2 and the counter electrode 3 comprise electrical conductors and it is advantageous to determine the best possible choice of materials for these conductors, by characterizing their electrochemical properties.

[0043] The electrolyte 4 ensures the passage of the ionic current and allows, where necessary, to avoid a short circuit between the working electrode 2 and the counter electrode 3 by direct contact of the latter.

[0044] A sensor 5 is a reference electrode made of lithium or sodium foil or other electrode metals. Ideally, a sensor 5 has a width of less than 1 millimeter, a length equal to the width of the central compartment, and a depth greater than or equal to 0.5 millimeters. In this embodiment, the sensor 5 is a potential sensor. The potential is induced by an accumulation of charges during the operation of the cell. The potential, at a given position, is measured relative to a reference point. Knowing this characteristic quantity makes it possible to determine other transport properties of the electrolyte 4, for example, the ionic conductivity or the diffusion coefficient, and to assess the actual performance of the cell 1 in terms of ionic transport.

[0045] In the example illustrated here, the electrochemical cell 1 has five sensors 5, in order to experimentally determine the potential profile along the cell 1, i.e., of the electrolyte 4. The more sensors 5 the electrochemical cell 1 has, the more precise and detailed the mapping of the cell 1's potential will be. The number of sensors 5 can be adjusted to suit the needs of the study.

[0046] The current collectors 6 are made of copper, aluminum, and / or any other noble metal. In the embodiment shown in Figures 1 to 5, the cell 1 comprises two current collectors 6, one connected to the working electrode 2 and the other to the counter electrode 3, and five potential collectors, each connected to a sensor 5. Preferably, the potential collectors 6 connected to the sensors 5 are copper wires with polytetrafluoroethylene (PTFE) or polyvinyl chloride (PVC) insulation, while the current collectors 6 connected to the working electrode 2 and the counter electrode 3 are copper foils.

[0047] The device 7 of the electrochemical cell 1 is shown in [Fig. 2]. It is parallelepiped-shaped, in order to avoid convection problems that could distort the measured results, and is machined using polyetheretherketone (PEEK). The device 7 comprises a lower support 8, a sealing gasket 9, and an upper support 10. The sealing gasket 9 separates the lower support 8 and the upper support 10.

[0048] Figures 3 and 4 illustrate the structure of the lower support 8. The lower support 8 has at least five compartments for storing elements of the electrochemical cell 1. It includes, firstly, a central compartment suitable for holding the solid electrolyte 4 and the sensors 5, a compartment containing the working electrode 2 and a compartment containing the counter electrode 3, both positioned at the ends of the central compartment, and two compartments suitable for accommodating two of the current collectors 6, both positioned at the ends of the lower support.

[0049] The central compartment has at least one groove comprising a sensor 5. In figures 1 to 8, the central compartment has five grooves for the five sensors 5a, 5b, 5c, 5d, 5e used.

[0050] Holes 11 are made on the lateral edges of the lower support 8 to allow the potential collectors 6 of the sensors 5 to pass through, as illustrated in [Fig. 4]. Similar configurations can be made for the other geometries indicated, the device 7 being able to be cylindrical, spherical, hemisphere or conical.

[0051] For the electrochemical characterization of cell 1, the galvano-static method, as illustrated in [Fig. 5], is used for example. The potentiostatic method can also be used.

[0052] Solid electrolytes are generally characterized at temperatures between 40°C and 200°C. Therefore, cell 1 is placed in a temperature-controlled chamber, and a polarization protocol using galvanostatic current is chosen to characterize a given electrolyte. Consequently, a potentiostat 12 electrically supplies the electrochemical cell 1 by applying a current across its terminals, between the working electrode 2 and the counter electrode 3. The current injected into cell 1 depends on its dimensions; typical values ​​can range from 1 microampere (PA) to several tens of milliamperes (mA). Thus, the electrochemical cell 1 connected to the potentiostat 12 can simulate a functioning battery.

[0053] A multi-channel multimeter 13 with very high input impedance (109 Q) is used to measure the voltages across the sensors 5. To do this, the connectors of the multimeter 13 are connected to the potential collectors 6 of the sensors 5 of the cell 1.

[0054] Figure 6 illustrates the principle of voltage measurement according to the galvanostatic method. The multimeter 13 measures the different voltages A4> between the sensors 5 or between the electrodes 2 and 3. Here, five voltages are recorded, A01 corresponding to the potential difference between sensor 5a and sensor 5e, A4>2 corresponding to the potential difference between sensor 5b and sensor 5e, A$3 corresponding to the potential difference between sensor 5c and sensor 5e, A04 corresponding to the potential difference between sensor 5d and sensor 5e, and Ad>we-ce corresponding to the potential difference between the working electrode 2 and the counter electrode 3.

[0055] The electrochemical protocol chosen to validate the installed cell 1 consists of applying a constant current Ip and measuring the evolution of the various voltages A closed A <bccv, est mesurée. Ensuite, durant une phase de relaxation, le courant appliqué Ip est nul, et la tension, nommée tension à circuit ouvert AOocv, est mesurée pendant un temps de relaxation tocv. Cette mesure de la tension permet d’obtenir un profil de potentiel et de concentration de la cellule, par application du courant constant. ​

[0056] The galvanostatic method is tested with a solid polymer electrolyte (PEO-LiTFSI) with different LiTFSI concentrations and at different operating temperatures. The experimental results, which validated the method, are shown in Figure 8. The measurements shown in Figure 8 were performed with a 1 mol / kg electrolyte, characterized at a temperature of 100°C and a current density of 1 A / m². Each measured potential difference A <j>1, A02, A03, AO4 and A <hwe-ce, est représentée sur le graphique en fonction du temps t, et selon les phases de polarisation et de relaxation. La courbe représentant A4> 4 has a lower potential difference than the others, the distance between sensors 5d and 5e being smaller than the distances between 5e and the other sensors 5c, 5b and 5a.

[0057] This mapping, showing the temporal evolution of the potential, makes it possible to evaluate the mobility of the ionic species in the electrolyte 4, and their ability to transport the electric current during the charging and discharging stages of the battery, taking into account the effect of the distribution of the concentration gradient.

[0058] The invention also relates to a method of assembling an electrochemical cell 1 such as that described above, the working electrode 2, the counter electrode 3, at least one sensor 5 and at least one potential collector 6 and the two current collectors 6 being integrated into a suitable device 7.

[0059] First, the sensor 5 must be prepared before being integrated into the lower support 8. This involves pre-cutting, preferably with scissors, the appropriate dimensions of lithium or sodium sheets, or any other metal ions depending on the application. Next, a sheathed copper wire serving as a potential collector 6, with a diameter identical to the diameter of the holes 11 and a length greater than 50 millimeters (as long as possible to facilitate electrical connections), is stripped at its ends to establish the electrical contacts of the sensor 5.Indeed, one end of the copper wire, stripped to a length identical to the width of the central compartment of the lower support 8 (ideally a copper diameter three times smaller than the depth of the grooves), is in direct contact with the lithium or sodium foil of the sensor 5, and the other stripped end of the copper wire is, for example, in contact with a connector of a multimeter 13, allowing it to capture the potential present at the sensors 5.

[0060] The sensors 5 thus prepared are inserted into the grooves of the central compartment of the lower support 8. The potential collectors 6 of the sensors 5 are also Inserted into the grooves of the central compartment, the potential collectors 6 protrude through the holes 11 made on the lateral edges of the lower support 8. Adhesive is used to bond the potential collectors 6 to the outer walls of the lower support 8, the sheath adhering readily to the adhesive. Care is taken to ensure that the adhesive does not come into contact with the grooves of the lower support 8, which could interfere with the measurements. Once the adhesive is dry, the potential collectors 6 are placed on lithium initially positioned in the grooves, and then more lithium is placed on top to completely fill the grooves and prevent unintentional movement of the sensors 5. If there is excess lithium in the grooves, a needle is used to remove it. The central compartment, designed to hold the solid electrolyte 4, is cleaned with dimethyl carbonate and dried at 100°C.This technique ensures good electrical contact between the potential collector 6 and the lithium sensor 5. Furthermore, precautions are taken to prevent the potential collectors 6 from coming into contact with the central electrolytic compartment, as this can cause problems in the potential readings.

[0061] After preparing the sensors 5 and inserting them into the lower support 8, the electrolyte 4 is inserted into its designated central compartment. According to one embodiment, the electrolyte 4 can be melted at 80°C.

[0062] Once the central electrolytic compartment is filled, sheets of lithium or sodium, or of any other metal ion depending on the application, used as working electrode 2 and counter electrode 3, are cleaned with dimethyl carbonate and cut to the correct dimensions. These sheets are identical in size to compartments 2 and 3, preferably with a length and width greater than or equal to 5 millimeters, and a thickness greater than or equal to 0.2 millimeters. They are then inserted into the corresponding compartments at the ends of the central electrolytic compartment.

[0063] The sealing gasket 9 is placed over the lower support 8.

[0064] The current collectors 6 of the working electrode 2 and the counter electrode 3 are placed under the lithium sheets, in their respective compartments at the ends of the lower support 8. To facilitate this step, the upper support 10 can be positioned on the assembly including the lower support 8 and the sealing gasket 9, and the cell 1 can be partially screwed in, before placing the current collectors 6.

[0065] After positioning the current collectors 6, the upper support 10 is placed on the assembly comprising the lower support 8 and the sealing gasket 9, and the cell 1 is fully screwed in.

[0066] Finally, cell 1 is sealed in a pocket of aluminum laminated film to make it airtight and watertight.

[0067] The assembly of cell 1 is prepared in a glove box under an argon atmosphere and all parts have been previously cleaned with dimethyl carbonate and dried at 100°C for twenty-four hours.

[0068] The position and width of the sensors 5, and the dimensions of the different elements of the device are variables of the invention.

[0069] This experimental solution can be used with an ion detector, with a tool for studying mass transfer phenomena, or with a concentration gradient measurement tool. The sensors of the electrochemical cell can be temperature measurement sensors and temperature gradient determinants.< / j>

Claims

Demands

1. Electrochemical cell (1) comprising a working electrode (2) and a counter electrode (3), a solid or viscous liquid electrolyte (4), at least one sensor (5) of a characteristic quantity of the cell, at least two current collectors (6), at least one potential collector (6), and a device (7) supporting the working electrode (2), the counter electrode (3), the electrolyte (4), the sensor (5), and the current and potential collectors (6), characterized in that the device (7) comprises a lower support (8), an upper support (10) and a seal (9) separating the lower support (8) and the upper support (10), and in that the lower support (8) comprises at least five compartments for storing electrochemical cell element (1), including a central compartment comprising the electrolyte (4) and the sensor (5),a compartment containing the working electrode (2) and a compartment containing the counter electrode (3), both positioned at the ends of the central compartment, and two compartments containing two of the current collectors (6), positioned at the ends of the lower support (8).

2. Electrochemical cell (1) according to claim 1, wherein the electrodes (2, 3) and the sensor (5) are lithium or sodium foils, and wherein the sensor (5) is a potential sensor.

3. Electrochemical cell (1) according to any one of claims 1 and 2, wherein the current collectors (6) are copper foils and the potential collector (6) is a copper wire comprising an insulator of polytetrafluoroethylene (PTFE) and / or polyvinyl chloride (PVC).

4. Electrochemical cell (1) according to any one of claims 1 to 3, wherein the electrolyte (4) comprises polymer and / or copolymer and / or ceramics and / or composites and / or gel used as solvents and at least one solute.

5. Electrochemical cell (1) according to any one of claims 1 to 4, wherein the device (7) is machined using polyetheretherketone (PEEK) and / or polytetrafluoroethylene (PTFE).

6. Electrochemical cell (1) according to any one of claims 1 to 5, wherein the central compartment of the lower support (8) has at least one groove comprising the sensor (5).

7. Electrochemical cell (1) according to any one of claims 1 to 6, wherein the current collectors (6) are suitable for being connected to a potentiostat (12) and / or a multimeter (13) in order to measure the characteristic quantity of the electrochemical cell (1).

8. Battery comprising a set of electrochemical cells (1) according to any one of claims 1 to 7.

9. A method for assembling an electrochemical cell (1) comprising a working electrode (2) and a counter electrode (3), a solid electrolyte (4), at least one sensor (5) of a characteristic quantity of the cell, at least two current collectors (6), at least one potential collector (6), and a device (7) supporting the working electrode (2), the counter electrode (3), the electrolyte (4), the sensor (5), and the current and potential collectors (6), characterized in that the device (7) comprises a lower support (8), an upper support (10) and a seal (9) separating the lower support (8) and the upper support (10), and in that the lower support (8) comprises a central compartment comprising the electrolyte (4) and the sensor (5), a compartment comprising the working electrode (2) and a compartment comprising the counter electrode (3), both positioned at the ends of the central compartment,and two compartments comprising two of the current collectors (6), positioned at the ends of the lower support (8), and comprising at least the following steps: - preparation of the sensor (5); - positioning of the sensor (5) in the central compartment, the central compartment comprising at least one groove suitable for receiving the sensor (5); - positioning of the electrolyte (4) in the central compartment; - positioning of the working electrode (2) and the counter electrode (3) in their respective compartments; placement of the sealing gasket (9) over the support lower (8); positioning of the current collectors (6) in their respective compartments; screwing the upper support (10) onto the lower support assembly (8) and the sealing gasket (9); insertion and sealing of the electrochemical cell (1) in an airtight and watertight pouch.

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