Method and apparatus for characterizing an electrochemical device during operation

Abstract

A method for characterizing an electrochemical device during operation, comprising connecting the electrochemical device to a power source and subsequently placing the electrochemical device in a sampler. The method further comprises testing a liquid electrolyte within the electrochemical device during operation by the sampler, detecting liquid decomposition products in the electrolyte, and analyzing the decomposition products, thereby characterizing the electrochemical device during operation.

Description

Cross-reference to related applications

[0001] This application claims priority from German patent application 10 2022 002 412.8, filed on June 28, 2022. The entire publication of German patent application 10 2022 002 412.8 is hereby incorporated by reference. Scope of the invention

[0002] The invention comprises a method and apparatus for characterizing an electrochemical device during operation. Background of the invention

[0003] A variety of in situ / in operando characterization tools and techniques have been and are being developed to investigate and understand the physicochemical limits and aging mechanisms of electrochemical energy storage devices. These techniques enable the development of improved electrolytes and electrode materials for electrochemical energy storage devices [see 1 - 7].

[0004] Such EES devices, such as electrochemical capacitors and batteries, are widespread in today's society. Electrochemical energy storage devices enable, for example, the use of electric vehicles (i.e., vehicles powered by an electric motor, such as cars, trains, or buses). Electrochemical energy storage devices also enable energy self-sufficiency.

[0005] However, EES devices have limitations regarding specific energy, i.e., how much charge can be stored in the electrochemical energy storage devices. Specific energy is the average available energy of the EES relative to its mass. Another limit is specific power, i.e., how quickly the energy is released by the electrochemical energy storage devices. Specific energy is the available energy normalized to the mass of the EES. When calculating these values, care must be taken to choose the definition of mass, as there are two possible values. In research, mass is defined as the mass of an active material. In other words, mass is equal to the weight of the material that actively stores the charge. In industry, mass is defined as the mass of the EES device, i.e., the cell, or of an entire battery pack.

[0006] Commercially available lithium-ion batteries generally have specific energy values ​​in the range of 100–300 Wh / kg and specific power values ​​in the range of 1000–3000 W / kg. Commercially available electric double-layer capacitors, also known as supercapacitors or ultracapacitors, achieve specific energy values ​​of approximately 5–10 Wh / kg and specific power values ​​of up to 25 kW / kg.

[0007] The lifetime of electrochemical energy storage devices is another limitation, e.g., cyclability (charge / discharge cycles) or stability in the charged state. An increase in specific energy, specific power, and lifetime is necessary to meet society's growing demand for renewable energy generation and storage [see 8, 9].

[0008] Aging processes occur in an electrolyte, an electrode and an electrolyte-electrode interphase in the EES devices during operation above their nominal parameters.

[0009] Primary aging processes include electrolyte-consuming and electrode pore-blocking side reactions in electrochemical capacitors. Primary aging processes also include mechanical detachment of the active material from the current collector, e.g., through delamination, and an increase in internal cell pressure. The increase in internal cell pressure is due to the development of volatile byproducts in the electrochemical capacitors. Expressions of primary aging processes include, for example, a decrease in capacitance and an increase in equivalent series resistance (ESR) [see 10-12].

[0010] Primary aging processes include parasitic side reactions, poor formation of the electrode-electrolyte interphase, dendrite formation, dissolution of the active material, decomposition of the electrolyte, delamination, gas evolution, and a pressure increase in the EES devices when the EES devices are batteries. The primary aging process leads to capacity loss, performance degradation, and an increase in ESR [see 13].

[0011] Observing and clarifying the side reactions that lead to cell aging in EES devices will provide the opportunity to optimize cell performance in EES devices. Cell performance can be optimized by adjusting the electrolyte and potentially developing additives to inhibit side reactions.

[0012] Various in-situ / in-operando techniques have been developed to investigate aging processes. For example, US patent application US 2020 / 0256921 A1 describes a chamber and system for real-time analysis of gas generated inside a secondary battery. The chamber comprises a first, insulating housing, a second, thermally conductive housing surrounding the first housing, and an inlet configured to be connected to a pump module for generating a flow of an induction medium into the chamber. The chamber further comprises an outlet for connecting an analysis module for analyzing the gas generated in the secondary battery by the flow of the induction medium.

[0013] Furthermore, the in-situ / in-operando techniques are intended to identify possible causes for the aging processes [see 1-7]. It is known that the terms "in-situ" and "in-operando" are often used synonymously. In this document, a clear distinction is made between the terms "in-situ" and "in-operando." The term "in-situ" is defined according to a Latin definition as "in its (original) location; in position / at the location in question." The term "in-operando" is defined as "working or in operation." In other words, the term "in-operando" includes an additional term for time-resolved measurements compared to the term "in-situ" [see 14, 15].

[0014] Time-resolved measurements refer to a type of experimental technique, i.e., a methodology that involves the collection and analysis of data at different points in time. The experimental technique of time-resolved measurements is useful for investigating dynamic processes or phenomena that occur within a specific time frame. Time-resolved measurements in the context of electrochemistry refer to the study of reactions that take place at an electrode interface or within an electrochemical cell. These time-resolved measurements allow researchers to track changes in various parameters of the electrochemical cell, such as potential, current, concentration, or spectroscopic properties, as a function of time.

[0015] Applications of in-situ / in-operando techniques for electrochemical capacitors and batteries are known and include, for example, calorimetry, simultaneous thermal analysis (STA), differential or online electrochemical mass spectroscopy (DEMS / OEMS), electrochemical quartz crystal microbalance (EQCM), (surface-enhanced) Raman spectroscopy (SERS, Raman), transmission electron microscopy (TEM), scanning electron microscopy (SEM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), nuclear magnetic resonance spectroscopy (NMR), electrochemical atomic force microscopy (EC-AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES), resonant inelastic X-ray scattering (RIXS) and small-angle X-ray scattering (SAXS).It should be noted that not every in-situ / in-operando technique can be used for the above-mentioned applications, since the different charge storage mechanisms of electrochemical capacitors and batteries, i.e., faradic, capacitive or pseudocapacitive, are different [see 1-7].

[0016] Kurzweil and Chwistek

[10] reported on investigations into the aging mechanisms and decomposition products of an electrolyte for electric double-layer capacitors (EDLCs). The electrolyte is a one-molar solution of tetraethylammonium tetrafluoroborate in acetonitrile. The investigations were carried out using gas chromatography-mass spectrometry (GC-MS). In 2021, Köps et al.

[17] showed that the choice of conducting salts for EDLCs influences the amount and type of decomposition products. Gachot et al.

[18] investigated the liquid and gas phase composition of carbonate-based Li-ion batteries using similar techniques.

[0017] The studies by Kurzweil and Chwistek, Köps et al., and Gachot et al. were conducted using a post-mortem approach. In this document, the term "post-mortem" refers to the disassembly of electrochemical cells and the analysis of parts of the disassembled electrochemical cells using various means. With the post-mortem method, it is not known what happens in the electrochemical cell on a time-resolved scale, as is the case with in-operando techniques.

[0018] The state of the art describes investigations into the aging mechanisms of electrochemical devices by analyzing the decomposition products in a liquid electrolyte using gas chromatography-mass spectrometry (GC-MS). The state of the art only includes investigations conducted using the post-mortem method.

[0019] Established automated liquid samplers and / or various autosampler systems are known for investigating, i.e., characterizing, trace amounts of dissolved analytes in a suitable solvent, i.e., a solvent in which the analytes are soluble. Established automated liquid samplers are suitable for investigating decomposition products in the electrolyte of electrochemical storage devices. Established automated liquid samplers are quite common in analytical, chemical, electrochemical, and materials development laboratories. The electrochemical cell can be used for electrochemical applications such as batteries, electrochemical capacitors (i.e., electrical double-layer capacitors or pseudocapacitors), hybrid devices, fuel cells, or electrocatalysts.

[0020] Float measurements, or "floating," are well-known methods for characterizing electrochemical energy storage devices, particularly double-layer capacitors. Float measurements test the stability of the electrochemical cell by holding a maximum nominal cell voltage for a specific time. The maximum nominal cell voltage depends on the choice of electrode and electrolyte. The maximum nominal cell voltage lies in the range of 2.7 to 3.0 V cell voltage for electrical double-layer capacitors, which, for example, comprise carbon-based electrodes in combination with an organic solvent, e.g., acetonitrile or propylene carbonate. The fixed time depends on the voltage applied to the electrochemical device and on the stability of the electrochemical cell. Typical values ​​for the fixation time reported in the literature range from 50 to 500 hours.

[0021] The remaining energy density, remaining capacity, and remaining capacity of the electrochemical cell are measured after the electrochemical cell has been held at the maximum rated voltage for a specified time. Float measurements provide an understanding of the degradation and stability of the electrochemical cell.

[0022] To the best of the inventors' knowledge, there are currently no methods available for either electrochemical capacitors or batteries that combine electrochemical measurements with in-operando analysis of the liquid electrolyte using GC-MS.

[0023] There is a need to measure electrochemical processes, such as energy and power storage, energy and power consumption, aging, resistance increase, corrosion, self-discharge, and plating of electrochemical devices during operation. Of interest are the decomposition reactions that occur in the electrode-electrolyte interface or in the electrolyte. The decomposition reactions that occur at the positive or negative electrode of electrochemical devices are also being investigated. Summary of the invention

[0024] This publication describes a method for characterizing an electrochemical device during operation. The electrochemical device is an energy storage and / or energy conversion device, such as an electrochemical capacitor, a battery, a hybrid of these two, a fuel cell, an electrochemical cell, or an electrocatalyst. The electrochemical device can be a single electrochemical cell or refer to a device comprising at least two electrochemical cells in series or parallel. An electrochemical cell comprises exactly one positive electrode and one negative electrode, and optionally a reference electrode, thus a maximum of three electrodes in total. The term "operation" refers to a period of time during which actions are performed on the electrochemical cell.In other words, the term "operation" refers to a period of time during which voltage or current is applied to the electrochemical device, i.e., the electrochemical cell. The method comprises connecting the electrochemical device to a power source. The power source is a device that provides energy or power in the form of current or electrical potential to the electrochemical device. The method further comprises connecting the electrochemical device to a sampler and sampling a liquid electrolyte in the one or more electrochemical cells in the sampler during operation. It is thus an in-operando technique. The method further comprises detecting liquid decomposition products in the electrolyte and analyzing the liquid decomposition products, thereby characterizing the electrochemical device during operation.The detection and analysis of the liquid decomposition products allows the determination of the chemical composition of the electrolyte.

[0025] In one embodiment, the characterization is performed using at least one of: impedance spectroscopy, charging and / or discharging, cyclic voltammetry, floating, pulsed charging, pulsed discharging, amperometry, voltammetry, or a combination thereof.

[0026] In another aspect, the sampler is selected from an automated liquid sampler or an autosampler system, wherein the autosampler system is preferably at least one gas chromatograph, a gas chromatograph coupled to a mass spectrometer, a gas chromatograph coupled to another detector, or a combination thereof.

[0027] In a further embodiment, the electrolyte is injected into a gas chromatograph after being removed from the electrochemical device. After injection, the liquid decomposition products are separated by gas chromatography before detection. Detection and analysis are performed using mass spectrometry.

[0028] In one embodiment, manual and / or automatic sampling from the electrochemical device is triggered by the power source.

[0029] Automated sampling enables time-resolved measurement and detection of liquid decomposition products. Automated sampling enables the investigation of specific aging processes within the electrochemical device.

[0030] In one embodiment, the current source is a potentiometer, a galvanostat, or a combination thereof.

[0031] In another aspect, the method further comprises disassembling the electrochemical device to remove components such as electrodes and electrolyte from the electrochemical device for post-mortem analysis.

[0032] This publication describes a device for carrying out the method. The device includes a means for taking a sample of the electrolyte from the electrochemical device during operation.

[0033] In one embodiment, the device comprises a spacer for separating the electrodes of the electrochemical element.

[0034] In another aspect, the device further comprises current collectors made of stainless steel, copper (Cu), aluminum (Al), titanium (Ti), platinum (Pt), or a combination thereof.

[0035] In one aspect, the electrochemical device comprises two or three electrodes located inside the electrochemical device. The electrodes are selected from at least one positive and one negative electrode. The electrochemical device further comprises at least two current collectors, an active material, a spacer, an electrolyte, and a septum. The septum is gas-tight and pierceable.

[0036] In one embodiment, the electrochemical device comprises three electrodes, one of which serves as a reference electrode. The electrochemical device enables detailed time-resolved measurements, i.e., insights into the formation and possible causes of degradation products in the electrochemical device. Furthermore, an electrochemical device with three electrodes enables the distinction between aging processes occurring at the positive electrode and the negative electrode.

[0037] In one embodiment, the detailed time-resolved measurements are performed between 5 and 10 minutes and up to 5 hours.

[0038] In one embodiment, the positive electrode and the negative electrode are separated by the spacer. The inventors have empirically found that an O-ring-shaped spacer with a notch on the top of the spacer allows sufficient diffusion of the liquid decomposition products from the electrode-electrode interphase toward the electrolyte. Sufficient diffusion of the liquid decomposition products enables detection of the liquid decomposition products by mass spectrometry (MS).

[0039] In one embodiment, the current collectors, electrodes, electrolyte, spacer and septum are removable and replaceable.

[0040] In another aspect, the automated liquid sampler (ALS) and / or autosampler system samples the electrolyte directly in the electrochemical device. In other words, the ALS takes a sample of the electrolyte and then injects it into a gas chromatograph with mass spectrometry (GC-MS).

[0041] In another aspect, the interior of the electrochemical device is assembled with seals. In other words, the electrolyte has no direct contact with the adhesive used.

[0042] In one embodiment, the electrochemical device is connected to a power source with several cables outside the ALS, preferably the power source is a potentiometer and / or a galvanostat.

[0043] In another aspect, the electrochemical device is mounted in an inert gas atmosphere.

[0044] In another aspect, the electrochemical device is assembled in an argon-filled glove box.

[0045] In another aspect, the electrochemical device is assembled and disassembled in air, in an oxygen-rich atmosphere, and in an inert gas atmosphere.

[0046] An electrochemical device is described that can be easily, i.e. freely, implemented into existing, i.e. commercially available, automatic liquid samplers and / or into various autosampler systems, i.e., it can be replaced in a few minutes using an original revolver placed in the ALS. When implementing the electrochemical cell into the existing automatic liquid samplers and / or into the various autosampler systems, certain requirements should be taken into account. One requirement relates to tightness. In other words, the electrochemical cell must be impermeable to liquids and gases. Another requirement relates to pierceability. In other words, a sampler must have access to the interior of the electrochemical cell, i.e., the electrolyte chamber. Impermeability to liquids and gases must be guaranteed.Another requirement relates to diffusion. The diffusion of liquid decomposition products from the electrode-electrolyte interphase into the electrolyte and within the electrolyte must be ensured, even if GC-MS can detect trace amounts of analytes. Another requirement relates to assembly. The electrochemical cell must be freely interchangeable with an original revolver of the automatic liquid sampler and / or capable of being integrated into other autosampler systems to enable direct sampling. Another requirement relates to durability. The electrochemical cell must withstand high currents and potentials as well as an aggressive chemical environment. Another requirement relates to performance. The electrochemical cell must exhibit similar electrochemical performance to common laboratory-scale cells, i.e., Swagelok® or button cell types.The device of the present invention meets all the above requirements. Description of the characters Fig. 1a-e are technical drawings of a gas chromatography-mass spectrometry (GC-MS) cell in operation. Fig. Figure 2 shows the capacitance and equivalent circuit resistance (ESR) of a negative electrode during the aging test of a positive electrode of an electrochemical cell. Fig. Figures 3a-c show charge-discharge profiles of the positive electrode and the (oversized) negative electrode at three different times during operation after 0, 15, and 30 hours. Fig. Figure 4 shows electrochemical impedance spectra of the positive electrode obtained every 5 hours during the positive electrode aging tests. Fig. Figure 5 shows a time-resolved total ion chromatogram obtained during the aging tests on the positive electrode. Fig. Figure 6 shows a method for characterizing an electrochemical device during operation. Fig. 7 shows a device for carrying out the method. Detailed description of the invention

[0047] The invention will now be described with reference to the drawings. It is understood that the embodiments and aspects of the invention described herein are only examples and do not limit the scope of the claims in any way. The invention is defined by the claims and their equivalents. It is understood that features of one aspect or embodiment of the invention may be combined with the feature of another aspect or other aspects and / or embodiments of the invention.

[0048] Electrochemical tests were performed, i.e., using a Biologic SP-150. Gas chromatography-mass spectrometry as sampler 20 was performed in step S50 using an Agilent 5977A EI-MSD - 7890 B GC system.

[0049] An electrochemical cell as part of an electrochemical device 10 was equipped with an Agilent 7683 series automatic liquid sampler 20 and an Agilent HP-5ms column (30 m, ID 0.25, DF 1, temperature range -60 to 325 / 350 °C). The temperature ramp applied was from 40 °C to 280 °C at 15 K min-1. The injection volume of the liquid samples from a liquid electrolyte 8 was set to 1 µL using a 10 µL syringe.

[0050] To prepare standard carbon electrodes 4, 3 g of the material were mixed with 90% Kuraray YP-50F, 5% IMERYS Super C65, and 5% Dow Chemical Walocell CMC in 8 ml of water to obtain a slurry (ink). The slurry was stirred for 30 minutes until a homogeneous suspension was obtained. The homogeneous suspension was cast onto aluminum foil using a doctor blade set to 150 µm. Circular cutouts were made from the aluminum foil using a home-made punching machine.

[0051] Oversized carbon electrodes 4 were prepared by mixing Kuraray YP-50F (85%) with IMERYS Super C65 (10%) and PTFE (10%) in 50 ml of ethanol (EtOH). After 2 hours of stirring and heating to 80 °C, a suspension was formed. The suspension was applied to a glass plate and rolled flat until a thickness of 1-2 mm was achieved. 5 mm thick electrodes 4 were punched and dried. A self-made spacer 3 served as a separating layer between the two electrodes 4.

[0052] The in-house manufactured spacer 3 was made of polyetherketone (PEEK) and had the shape of an O-ring with a notch on top of the spacer 3. The spacer 3 allowed sufficient diffusion of liquid decomposition products from the electrode-electrode interphase into the electrolyte 3 of the electrochemical device 10. The use of a commonly used separator, i.e., a spacer 3, e.g., made of paper, polymer, or a glass fiber membrane, pressed between the two electrodes 4, was not performed because this commonly used separator does not allow sufficient diffusion of the liquid decomposition products. This lack of sufficient diffusion leads to a much higher detection limit, which reduces the quality of the method. It is clear that sufficient amounts of liquid decomposition products are required to generate a suitable signal during analysis.The amount of liquid decomposition products required depends on the analytical instruments and the analytes.

[0053] A 1 M solution of tetraethylammonium tetrafluoroborate (Et4NBF4) (Sigma Aldrich) in acetonitrile (ACN) (Sigma Aldrich) was chosen as electrolyte 8. Electrolyte 8 was prepared in an argon-filled dry box (Labmaster Pro, MBraun). All solid materials used were dried in a vacuum glass oven. The solvent was dried with 3 Å molecular sieves (Koestrolite). The water content of electrolyte 8 was determined to be below 20 ppm by Karl Fischer titration.

[0054] An electrochemical three-electrode in-operando GC-MS cell 10 was developed as an electrochemical device 10 and is in the Fig. 1a-e. The electrochemical in-operando GC-MS cell 10 with three electrodes is made of polyetherketone (PEEK).

[0055] No adhesive was used in the manufacture and assembly of the electrochemical three-electrode in-operando GC-MS cell. All helical parts are sealed with gaskets and / or septa made of either fluoroelastomers (Viton®) or polytetrafluoroethylene (PTFE).

[0056] Two current collectors 1 and 2 were used. The two current collectors 1 and 2 were made of stainless steel (1.4301, X5CrNi18-10). A silver wire (Alfa Aesar, 99.9985%) was used as reference electrode 5.

[0057] The GC-MS cell 10 was mounted in an argon-filled dry box and filled with 1000-1200 µl of the electrolyte 8.

[0058] In a demonstration example, the GC-MS cell 10 was constructed symmetrically, i.e., with two standard electrodes 4. The symmetrical construction is used when, in step S60, processes occurring simultaneously at both standard electrodes 4 are to be characterized. In the example, processes occurring at one of the standard electrodes 4 cannot be characterized.

[0059] In another example, the GC-MS cell 10 was constructed asymmetrically, ie with a standard electrode 4 and an oversized electrode 4. The asymmetric construction is used when, in step S60, processes that take place at a single electrode are to be characterized.

[0060] The applied potentials are either positive or negative depending on the characterized electrode 4. A standard electrode 4 was used as the positive electrode and an oversized electrode 4 was used as the negative electrode for the positive electrode investigation.

[0061] Fig. 6 illustrates a method for characterizing the electrochemical device 10 during operation. The method comprises connecting the electrochemical device 10 to a power source 15 in a connection step S10 and subsequently placing the electrochemical device 10 in the sampler 20 in a placement step S20. The method further comprises sampling the liquid electrolyte 8 in one or more electrochemical cells in the electrochemical device 10 by the sampler 20 during operation in a sampling step S30. Following the sampling step S30, liquid decomposition products in the electrolyte 8 are detected in a detection step 40, and the liquid decomposition products are analyzed in an analysis step 50. The detection step 40 and the analysis step 50 of the liquid decomposition products are carried out, for example, by means of mass spectrometry.

[0062] In the example, the sampler is an automated liquid sampler (ALS). The sampling step S30, i.e., the sampling step, comprises, for example, piercing a septum 9 of the electrochemical device 10 with a needle of the automated liquid sampler. A liquid sample is taken from the liquid electrolyte 8 and injected into a gas chromatograph 20-mass spectrometer in an injection step S33.

[0063] In a further example, the method comprises a separation step S35 for separating the liquid decomposition products by means of gas chromatography after the injection step S33.

[0064] Fig. Figure 7 shows a schematic representation of a device 100 for carrying out the method described in this description. The device 100 comprises the electrochemical device 10, which is connected to a power source 15. The electrochemical device 10 comprises one or more electrochemical cells containing the liquid electrolyte 8 within the electrochemical device 10. The device 100 further comprises the sampler 20, in which the electrochemical device 10 is placed. The sampler 20 is designed to extract the liquid electrolyte 8 during operation in the sampling step S30. The device 100 comprises a detector 25 for detecting the liquid decomposition products in the electrolyte 8 in the detection step 40 and analyzing them in the analysis step 50.

[0065] In one example, the device 100 includes an extractor 30 for withdrawing a liquid sample of the electrolyte 8 from the electrochemical device 10 during operation.

[0066] The electrochemical device 10 also includes current collectors 1, 2 made of stainless steel, copper (Cu), aluminum (Al), titanium (Ti), platinum (Pt) or a combination thereof.

[0067] In one example, the electrochemical device 10 further comprises two or three electrodes 4 located inside the electrochemical device 10, as shown in Fig. 1c. The electrodes 4 are selected from at least one positive and one negative electrode. The electrochemical device 10 further comprises an active material 12 and the septum 9. The septum 9 is gas-tight and pierceable. The GC-MS cell 10 was electrochemically cycled in the following sequence: Electrochemical impedance spectroscopy (EIS) for analysis step S50 was performed in the range of 500 kHz to 10 mHz. The EIS was followed by three cycles of galvanostatic charging and discharging to a set potential of 1 V versus Ag / Ag+ using a current source 15, i.e., a galvanostat.

[0068] The three cycles of galvanostatic charge and discharge were followed by a floating test as a further analysis in step 50. The floating test lasted 1 hour at the previously set potential of 1 V versus Ag / Ag+ and was repeated five times. The set voltage was increased by 0.25 V after the five repetitions, after which the sequence was repeated. The voltage was increased by another 0.25 V to 1.5 V versus Ag+ / Ag.

[0069] The increase of the set voltage was repeated until a voltage of 2.25 V vs. Ag / Ag+ was reached.

[0070] The measurement concluded with a final EIS measurement as a further analysis in step 50. A liquid sample was automatically extracted by an extractor 30 via the automatic liquid sampler 20, i.e., taken, injected in step S33, and analyzed by GC-MS in step S50. Floating was performed five times for one hour at a potential, and only then was the voltage increased, so that the floating time per potential was 5 hours.

[0071] Fig. Figure 2 shows a calculated capacitance (F g-1) and an equivalent series resistance (ESR, Ω cm2) as a function of accumulated holding time. The applied potential is determined as in Fig. 2, increased by 0.25 V for every 5 hours of floating. The capacity and ESR show stable values ​​until a potential of 1.75 V vs. Ag / Ag+ is reached. A sharp decrease in capacity and an increase in ESR are observed at potentials of more than 2 V vs. Ag / Ag+. This indicates significant aging of the GC-MS cell and thus the formation of liquid decomposition products.

[0072] Fig. 3a-c show a selection of galvanostatic charge-discharge profiles of the positive standard electrode 4 (thick gray) and the negative oversized electrode 4 (thin black) at three different time points, i.e., at 0, 15, and 30 hours during operation.

[0073] At 0 hours (set potential of 1 V vs. Ag / Ag+) and at 15 hours (set potential of 1.50 V vs. Ag / Ag+), the two electrodes exhibit ideal EDLC-like linear behavior. At 30 hours (set potential of 2.25 V vs. Ag / Ag+), the profiles show a curved line. This example demonstrates severe degradation of the electrode 4 - electrolyte 8 interphase. The negative electrode 4 shifts further toward the negative potential as aging processes occur at the positive electrode 4. This shift was expected and attributed to irreversible oxidation at the positive electrode 4. The irreversible oxidation leads to an accumulation of electrons at the negative electrode. The shift can be neglected as long as the negative electrode 4 remains within the stability window of the characterized electrochemical device 10.The stability window is the potential range within which the system under investigation, i.e., the characterized electrochemical element 10, is stable, meaning that no degradation of the electrode-electrolyte interphase occurs. The displacement has no influence on the voltage measurement as long as the displacement of the electrodes 4 does not exceed the respective stability limits, i.e., the stability window.

[0074] Fig. Figure 4 shows Nyquist plots of the obtained impedance spectra. An EDLC-like impedance spectrum was obtained, represented by a small semicircle followed by a steep rise in the imaginary part at the beginning of operation. With increasing floating time and potential, this value shifts slightly to higher resistances. The resistance increases after 20 hours of floating (set potential of 1.75 vs. Ag / Ag+). The resistance demonstrates the properties of a laboratory-scale EDLC. The resistance only increases after reaching a potential of 2.00 V vs. Ag+ / Ag, which corresponds to a floating time of 20 hours. A missing semicircle indicates a strong degradation of the electrode-electrolyte interphase and a sharp increase in the internal resistances.

[0075] Fig.Figure 5 shows the three-dimensional time-resolved total ion chromatograms (TICs) from in-operando GC-MS measurements. The measurements were performed during aging tests on the positive electrode.

[0076] Samples of electrolyte 8 were taken in-operando every 5 hours using sampler 20 and analyzed by GC-MS in analysis step S50. After injecting the sample into the gas chromatography system in injection step S33, mass spectra were continuously recorded. Various analytes were separated by gas chromatography in separation step S35 and subsequently detected in the mass spectrometer (MS). The resulting mass spectra were compared with NIST databases. Possible liquid decomposition products were detected and identified in detection step S40.

[0077] TICs display an accumulated intensity, relative abundance, across a detected mass range at each time point of the analysis as a function of time, i.e., the retention time (tR) of the analytes. Each peak in the spectra correlates with a specific mass spectrum and indicates a specific degradation product. The characteristic retention time of each compound in the liquid degradation products does not change as long as the analysis parameters remain unchanged.

[0078] Comparing the obtained TICs, a first peak appears at 1.75 versus Ag / Ag+. The height and area increase with increasing potential. Furthermore, the total amount of detected signals increases with increasing potential. This demonstrates the greater degradation at higher potentials.

[0079] During the aging tests, four degradation products were identified and assigned to the aging processes occurring at the positive electrode: acetamide (tR of 8 min), N-ethylacetamide (tR of 12 min), 2,4,6-trimethyl-1,3,5-triazine (tR of 12.5 min), and diacetamide (tR of 14 min). Acetamide, N-ethylacetamide, and diacetamide are oxidation and hydrolysis products of the solvent acetonitrile. 2,4,6-trimethyl-1,3,5-triazine is a trimerization and cyclization product of acetonitrile. This demonstrates that the oxidation states of the liquid decomposition products do not change. In other words, no electrons are consumed in the electrochemical device 10. The inventors assumed that cyclization is a surface-limited reaction, requiring partial oxidation during the surface-limited reaction. References (1) Pal, B.; Yasin, A.; Kaur, R.; Tebyetekerwa, M.; Zabihi, F.; Yang, S.; Yang, C. C.; Sofer, Z.; Jose, R. Understanding Electrochemical Capacitors with In-Situ Techniques. Erneuern. Sustain. Energy Rev. 2021, 149, 111418. https: / / doi.org / 10.1016 / J.RSER.2021.111418. (2) Patra, A.; K., N.; Jose, J. R.; Sahoo, S.; Chakraborty, B.; Rout, C. S. Understanding the Charge Storage Mechanism of Supercapacitors: In Situ / Operando Spektroskopische Ansätze und theoretische Untersuchungen. J. Mater. Chem. A 2021, 9 (46), 25852-25891. https: / / doi.org / 10.1039 / D1TA07401F. (3) Lin, Z.; Taberna, P. L.; Simon, P. Advanced Analytical Techniques to Characterize Materials for Electrochemical Capacitors. Curr. Opin. Electrochem. 2018, 9, 18-25. https: / / doi.org / 10.1016 / J.COELEC.2018.03.004. (4) Hu, J. Z.; Jaegers, N. R.; Hu, M. Y.; Mueller, K. T. In Situ and Ex Situ NMR for Battery Research. J. Phys. Condens. Matter 2018, 30 (46), 463001. https: / / doi.org / 10.1088 / 1361-648X / AAE5B8. (5) Tripathi, A. M.; Su, W. N.; Hwang, B. J. In Situ Analytical Techniques for Battery Interface Analysis. Chem. Soc. Rev. 2018, 47 (3), 736-751. https: / / doi.org / 10.1039 / C7CS00180K. (6) Li, H.; Guo, S.; Zhou, H. In-Situ / Operando Characterization Techniques in Lithium-Ion Batteries and Beyond. J. Energy Chem. 2021, 59, 191-211. https: / / doi.org / 10.1016 / J.JECHEM.2020.11.020. (7) Noväk, P.; Panitz, J. C.; Joho, F.; Lanz, M.; Imhof, R.; Coluccia, M. Advanced in Situ Methods for the Characterization of Practical Electrodes in Lithium-Ion Batteries. J. Power Sources 2000, 90 (1), 52-58. https: / / doi.org / 10.1016 / S0378-7753(00)00447-X. (8) Goodenough, J. B.; Park, K. S. The Li-Ion Rechargeable Battery: A Perspective. J. Am. Chem. Soc. 2013, 135 (4), 1167-1176. https: / / doi.org / 10.1021 / JA3091438 / AS-SET / IMAGES / MEDIUM / JA-2012-091438_0009.GIF. (9) Simon, P.; Gogotsi, Y. Perspectives for Electrochemical Capacitors and Related Devices. Nat. Mater. 2020 1911 2020, 19 (11), 1151-1163. https: / / doi.org / 10.1038 / s41563-020-0747-z. (10) Kurzweil, P.; Chwistek, M. Electrochemical Stability of Organic Electrolytes in Supercapacitors: Spektroskopie und Gasanalyse von Zersetzungsprodukten. J. Power Sources 2008, 176 (2), 555-567. https: / / doi.org / 10.1016 / j.jpowsour.2007.08.070. (11) Ruch, P. W.; Cericola, D.; Foelske-Schmitz, A.; Kötz, R.; Wokaun, A. Aging of Electrochemical Double Layer Capacitors with Acetonitrile-Based Electrolyte at Elevated Voltages. Electrochim. Acta 2010, 55 (15), 4412-4420. https: / / doi.org / 10.1016 / j.electacta.2010.02.064. (12) Ruch, PW; Cericola, D.; Foelske, A.; Kötz, R.; Wokaun, A. A Comparison of the Aging of Electrochemical Double Layer Capacitors with Acetonitrile and Propylene Carbonate-Based Electrolytes at Elevated Voltages. Electrochim. Acta 2010, 55 (7), 2352-2357. https: / / doi.org / 10.1016 / j.electacta.2009.11.098. (13) Kabir, M.M.; Demirocak, DE Degradation Mechanisms in Li-Ion Batteries: A State-of-the-Art Review. Int. J. Energy Res. 2017, 41 (14), 1963-1986. https: / / doi.org / 10.1002 / ER.3762. (14) Bañares, MA: Operando methodology: combining in situ spectroscopy and simultaneous activity measurements under catalytic reaction conditions. Catal. Today 2005, 100 (1-2), 71-77. https: / / doi.org / 10.1016 / J.CA TTOD.2004.12.017. (15) Oxford English Dictionary https: / / www.oed.com / (accessed 4 February 2022). (16) Hess, LH; Bothe, A.; Balducci, A. Design and use of a novel in-situ simultaneous thermal analysis cell for accurate “real-time” monitoring of heat and weight changes in electrochemical capacitors. Energy Technol. 2021, 9 (9), 2100329. https: / / doi.org / 10.1002 / ente.202100329. (17) Köps, L.; Kreth, FA; Bothe, A.; Balducci, A. High Voltage Electrochemical Capacitors Operating at Elevated Temperature Based on 1,1-Dimethylpyrrolidinium Tetrafluoroborate. Energy storage material. 2021, 44, 66-72. https: / / doi.org / 10.1016 / j.ensm.2021.10.006. (18) Gachot, G.; Ribière, P.; Mathiron, D.; Grugeon, S.; Armand, M.; Leriche, J.B.; Pilard, S.; Laruelle, S. Gas Chromatography / Mass Spectrometry as a Suitable Tool for the Li-Ion Battery Electrolyte Degradation Mechanisms Study. Anal. Chem. 2011, 83 (2), 478-485. https: / / doi.org / 10.1021 / AC101948U / ASSET / IMAGES / MEDIUM / AC-2010-01948U_0007.GIF. Reference symbol 1, 2 pantographs 3 spacers 4 electrodes (positive and negative electrode) 5 Reference electrode 6, 7 seals 8 Electrolyte 9 Partition / Seal 10 electrochemical device 12 active material 15 Power source 20 samplers 25 detector 30 pullers 100 device QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2022 002 412.8

[0001] DE 10 2022 002

[0001] US 2020 / 0256921 A1

[0012] Cited non-patent literature

[0000] Köps et al.

[17] showed in 2021

[0016] Pal, B.; Yasin, A.; Kaur, R.; Tebyetekerwa, M.; Zabihi, F.; Yang, S.; Yang, C.C.; Sofer, Z.; Jose, R. Understanding Electrochemical Capacitors with In-Situ Techniques. Renew. Sustain. Energy Rev. 2021, 149, 111418. https: / / doi.org / 10.1016 / J.RSER.2021.111418

[0079] Patra, A.; K., N.; Jose, J.R.; Sahoo, S.; Chakraborty, B.; Rout, C.S. Understanding the Charge Storage Mechanism of Supercapacitors: In Situ / Operando Spectroscopic Approaches and Theoretical Investigations. J. Mater. Chem. A 2021, 9 (46), 25852–25891. https: / / doi.org / 10.1039 / D1TA07401F

[0079] Lin, Z.; Taberna, P.L.; Simon, P. Advanced Analytical Techniques to Characterize Materials for Electrochemical Capacitors. Curr. Opin. Electrochem. 2018, 9, 18-25. https: / / doi.org / 10.1016 / J.COELEC.2018.03.004

[0079] Hu, J. Z.; Jaegers, N. R.; Hu, M. Y.; Mueller, K. T. In Situ and Ex Situ NMR for Battery Research. J. Phys. Condens. Matter 2018, 30 (46), 463001. https: / / doi.org / 10.1088 / 1361-648X / AAE5B8

[0079] Tripathi, A. M.; Su, W. N.; Hwang, B. J. In Situ Analytical Techniques for Battery Interface Analysis. Chem. Soc. Rev. 2018, 47 (3), 736-751. https: / / doi.org / 10.1039 / C7CS00180K.

[0079] Li, H.; Guo, S.; Zhou, H. In-Situ / Operando Characterization Techniques in Lithium-Ion Batteries and Beyond. J. Energy Chem. 2021, 59, 191-211. https: / / doi.org / 10.1016 / J.JECHEM.2020.11.020

[0079] Noväk, P.; Panitz, J. C.; Joho, F.; Lanz, M.; Imhof, R.; Coluccia, M. Advanced in Situ Methods for the Characterization of Practical Electrodes in Lithium-Ion Batteries. J. Power Sources 2000, 90 (1), 52-58. https: / / doi.org / 10.1016 / S0378-7753(00)00447-X.

[0079] Goodenough, J. B.; Park, K. S. The Li-Ion Rechargeable Battery: A Perspective. J. Am. Chem. Soc. 2013, 135 (4), 1167-1176. https: / / doi.org / 10.1021 / JA3091438 / AS-SET / IMAGES / MEDIUM / JA-2012-091438_0009.GIF

[0079] Simon, P.; Gogotsi, Y. Perspectives for Electrochemical Capacitors and Related Devices. Nat. Mater. 2020 1911 2020, 19 (11), 1151-1163. https: / / doi.org / 10.1038 / s41563-020-0747-z.

[0079] Kurzweil, P.; Chwistek, M. Electrochemical Stability of Organic Electrolytes in Supercapacitors: Spektroskopie und Gasanalyse von Zersetzungsprodukten. J. Power Sources 2008, 176 (2), 555-567. https: / / doi.org / 10.1016 / j.jpows

[0079] Ruch, P. W.; Cericola, D.; Foelske-Schmitz, A.; Kötz, R.; Wokaun, A. Aging of Electrochemical Double Layer Capacitors with Acetonitrile-Based Electrolyte at Elevated Voltages. Electrochim. Acta 2010, 55 (15), 4412-4420. https: / / doi.org / 10.1016 / j.electacta.2010.02.064

[0079] Ruch, PW; Cericola, D.; Foelske, A.; Kötz, R.; Wokaun, A. A Comparison of the Aging of Electrochemical Double Layer Capacitors with Acetonitrile and Propylene Carbonate-Based Electrolytes at Elevated Voltages. Electrochim. Acta 2010, 55 (7), 2352-2357. https: / / doi.org / 10.1016 / j.electacta.2009.11.098

[0079] Kabir, M.M.; Demirocak, DE Degradation Mechanisms in Li-Ion Batteries: A State-of-the-Art Review. Int. J. Energy Res. 2017, 41 (14), 1963-1986. https: / / doi.org / 10.1002 / ER.3762

[0079] Bañares, MA: Operando methodology: Combining in situ spectroscopy and simultaneous activity measurements under catalytic reaction conditions. Catal. Today 2005, 100 (1-2), 71-77. https: / / doi.org / 10.1016 / J.CA TTOD.2004.12.017

[0079] Oxford English Dictionary https: / / www.oed.com / (accessed 4 February 2022

[0079] Hess, LH; Bothe, A.; Balducci, A. Design and use of a novel in-situ simultaneous thermal analysis cell for accurate "real-time" monitoring of heat and weight changes in electrochemical capacitors. Energy Technol. 2021, 9 (9), 2100329. https: / / doi.org / 10.1002 / ente.202100329

[0079] Köps, L.; Kreth, FA; Bothe, A.; Balducci, A. High Voltage Electrochemical Capacitors Operating at Elevated Temperature Based on 1,1-Dimethylpyrrolidinium Tetrafluoroborate. Energy storage material. 2021, 44, 66-72. https: / / doi.org / 10.1016 / j.ensm.2021.10.006

[0079] Gachot, G.; Ribière, P.; Mathiron, D.; Grugeon, S.; Armand, M.; Leriche, J.B.; Pilard, S.; Laruelle, S. Gas Chromatography / Mass Spectrometry as a Suitable Tool for the Li-Ion Battery Electrolyte Degradation Mechanisms Study. Anal. Chem. 2011, 83 (2), 478-485. https: / / doi.org / 10.1021 / AC101948U / ASSET / IMAGES / MEDIUM / AC-2010-01948U_0007.GIF

[0079]

Claims

[1] A method for characterizing an electrochemical device (10) during operation, comprising: Connecting (S10) the electrochemical device (10) to a power source (15), followed by inserting (S20) the electrochemical device (10) into a sampler (20); sampling (S30) of a liquid electrolyte (8) in one or more electrochemical cells in the electrochemical device (10) by the sampler (20); Detection (S40) of liquid decomposition products in the electrolyte (8); and analysis (S50) of the liquid decomposition products, whereby the characterization (S60) of the electrochemical device (10) takes place during operation. [2] The method according to claim 1, wherein the characterization (S60) is performed by means of at least one of: impedance spectroscopy, charging and / or discharging, cyclic voltammetry, floating, pulsed charging, pulsed discharging, amperometry, voltammetry or a combination thereof. [3] The method according to claim 1 or 2, wherein the sampler (20) is an automatic liquid sampler or an autosampler system, wherein the autosampler system is preferably at least one of the following: a gas chromatograph, a gas chromatograph coupled to a mass spectrometer, a gas chromatograph coupled to a detector such as a flame ionization detector (FID), a thermal conductivity detector (TCD) or an electron capture detector (ECD). [4] A method according to any one of the above claims, wherein: After the removal (S30) the liquid electrolyte (8) is injected (S33) into a gas chromatograph; the injection (S33) is followed by separation (S35) of the liquid decomposition products by gas chromatography before detection (S40); and wherein the detection (S40) and the analysis (S50) are carried out by mass spectrometry. [5] Method according to one of the above claims, wherein the current source (15) is a potentiometer, a galvanostat or a combination thereof. [6] Method according to one of the above claims, wherein the withdrawal (S30) and the injection (S33) are triggered automatically and / or manually during operation by one of the power sources (15) or by an external device of the electrochemical device (10), preferably a potentiometer. [7] A method according to any one of the above claims, further comprising disassembling (S70) the electrochemical device (10) to remove components, such as electrodes (4) and electrolyte (8), from the electrochemical device (10) for post-mortem analysis. [8] Apparatus (100) for performing a method for characterizing an electrochemical device (10) during operation, comprising: the electrochemical device (10) connected to a power source (15), the electrochemical device (10) comprising a liquid electrolyte (8) in one or more electrochemical cells; a sampler (20) in which the electrochemical device (10) is placed, wherein the sampler (20) is suitable for sampling the liquid electrolyte (8) during operation; and a detector (25) for detecting and analyzing liquid decomposition products in the electrolyte (8). [9] Apparatus according to claim 8, further comprising an extractor (30) for withdrawing a liquid sample of the electrolyte (8) from the electrochemical device (10) during operation. [10] Device according to claim 8 or 9, further comprising a spacer (3) for separating the electrodes (4) of the electrochemical device (10). [11] Device according to claims 8 to 10, further comprising current collectors (1, 2) made of stainless steel, copper (Cu), aluminum (Al), titanium (Ti), platinum (Pt) or a combination thereof.

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