Metal-sulfur battery cell with a sensor device, metal-sulfur battery with metal-sulfur battery cells and system for investigating chemical processes in a metal-sulfur battery cell

Abstract

Metal-sulfur battery cell (100), in particular pouch cell, with a cell housing (52) in which at least one anode (54) and at least one cathode (58) are arranged, which are separated by a separator (56), and with a sensor device (50) for investigating chemical processes in the battery cell (100), wherein the sensor device (100) comprises at least one optical fiber (20) for transmitting at least one light beam (12), wherein the at least one optical fiber (20) has at least one first fiber section (21) for light transmission out of the first fiber section (21) and / or into the first fiber section (21), wherein the at least one optical fiber (20) is arranged at least partially in the cell housing (52), wherein at least the first fiber section (21) is arranged within the cell housing (52).

Description

State of the art

[0001] The invention relates to a metal-sulfur battery cell, in particular a pouch cell, a metal-sulfur battery with a plurality of metal-sulfur battery cells, in particular pouch cells, a system for investigating chemical processes in a metal-sulfur battery cell, in particular a pouch cell, and the use of a calibrated optical fiber in a sensor device for investigating chemical processes in a metal-sulfur battery cell, in particular a pouch cell.

[0002] In metal-sulfur battery cells, such as lithium-sulfur battery cells, the electrolyte / sulfur ratio, expressed in milliliters per gram of sulfur (ml / g), is a critical parameter for application. Since the electrolyte is a passive component, a ratio of no more than 5, ideally between 3 and 5, is targeted for practical cells to achieve the highest possible energy density. For operando investigations of chemical processes in lithium-sulfur battery cells using UVVIS spectroscopy (spectroscopy in visible light (VIS) and ultraviolet (UV)), special cell designs are currently required. Special battery cells with optical windows are widely used. These typically require a very large amount of electrolyte, which is far removed from any practical application.

[0003] In the case of pouch cells, a hole is cut in the cell packaging film (the so-called pouch bag) and an optical window is inserted. In addition, specially prepared electrodes must be used. Depending on the process being studied, either the current collector film must be removed to make the cathode optically accessible, or a hole is punched in the cathode to visualize the separator and the species dissolved in the electrolyte.

[0004] The use of specialized laboratory cells for UVVIS operando measurements results in a high electrolyte excess. This significantly influences the processes occurring during battery cell cycling and does not reflect the behavior during operation in a real-world application battery cell. Particularly in lithium-sulfur battery cells, the polysulfides formed during cycling exhibit very high solubility in many electrolytes.

[0005] In current pouch cell applications with optical windows, holes are punched into the electrodes under investigation to allow for the analysis of polysulfides. This necessitates filling a large dead volume and results in inhomogeneous current densities on the electrode surface. Prior art techniques include operando investigations at an electrolyte / sulfur ratio of 60. Disclosure of the invention

[0006] The object of the invention is to create an improved metal-sulfur battery cell, in particular a pouch cell, with a sensor device for investigating chemical processes in the battery cell.

[0007] Another task is to create a metal-sulfur battery with a plurality of such metal-sulfur battery cells, especially pouch cells.

[0008] Another task is to create an improved system for investigating chemical processes in a metal-sulfur battery cell, especially a pouch cell, using a sensor device.

[0009] Another task is to specify a use of a calibrated optical fiber in a sensor device for investigating chemical processes in a metal-sulfur battery cell, in particular a pouch cell.

[0010] The problems are solved by the features of the independent claims. Favorable embodiments and advantages of the invention become apparent from the further claims, the description, and the drawings.

[0011] According to one aspect of the invention, a metal-sulfur battery cell, in particular a pouch cell, is proposed, comprising a cell housing in which at least one anode and at least one cathode are arranged, separated by a separator, and a sensor device for investigating chemical processes in the battery cell, wherein the sensor device comprises at least one optical fiber for transmitting at least one light beam. The at least one optical fiber has at least one first fiber section for light transmission out of and / or into the first fiber section.

[0012] The at least one optical fiber is arranged at least partially within the cell housing, with at least the first fiber section being arranged within the cell housing.

[0013] The proposed metal-sulfur battery cell features a sensor device in the form of a first fiber segment for light transmission, which can be operated as a so-called Fiber Optical Evanescent Wave Sensor (FOEWS). This makes it possible to investigate the chemical processes during the operation of a metal-sulfur battery cell using spectroscopy, for example, in the UV-VIS range from 200 nm to 1100 nm. Particularly in a pouch cell design, the optical fiber can be conveniently inserted into the cell housing, in this case the pouch bag, and integrated into an electrode stack without modifying the pouch bag or the electrodes.

[0014] In contrast to operando measurement using conventional optical measuring cells, the pouch cell used requires a very low electrolyte excess, which is very close to an electrolyte / sulfur ratio relevant for the application of at most 5, in particular between at least 3 and at most 5.

[0015] The sensor device is advantageously calibrated with electrolyte and reference solutions containing defined polysulfide solutions. This allows the actual absorption of the sensor device, particularly of the first fiber segment, to be determined and a quantitative analysis of the polysulfide species to be performed.

[0016] Metal-sulfur systems can include, for example, lithium-sulfur, magnesium-sulfur, or calcium-sulfur.

[0017] The advantage of metal-sulfur batteries is their high specific energy density. A crucial factor for their practical application is the so-called polysulfide shuttle. The high solubility of sulfur in the liquid system presents an inherent problem that has not yet been solved, particularly for high-energy-density cells, which require a high sulfur content in the cathode. In the proposed metal-sulfur battery cell, fiber optic sensors enable the detection and analysis of this polysulfide shuttle.

[0018] Being able to analyze this solubility behavior of sulfur, also called polysulfide species, in application-relevant cell formats such as pouch cells represents a very large added value for the research and development of metal-sulfur batteries.

[0019] The proposed battery cell allows for the precise investigation of the chemical processes in metal-sulfur batteries. This is fundamentally possible in all applications where metal-sulfur batteries are used, such as aircraft, motor vehicles, satellites, spacecraft, ships, railways, or stationary electrical storage systems.

[0020] In a favorable embodiment of the battery cell, at least the first fiber section can be arranged, and in particular embedded, in the cell housing between the anode and the separator, or between the separator and the cathode, or within the cathode. In this way, the concentration of dissolved polysulfide species can be advantageously determined via the absorption of the incident light beam, which is characteristic of the concentration of dissolved polysulfide species.

[0021] With a favorable design of the battery cell, the first fiber segment can be configured as an evanescent wave sensor. The concentration of the polysulfide species can then be determined using evanescent wave spectroscopy.

[0022] With a favorable battery cell design, at least one optical fiber can be calibrated such that the calibrated fiber exhibits a correlation between a wavelength of the incident light beam and the absorption of the light beam in an environment with varying concentrations of dissolved sulfur and / or dissolved sulfur compounds. The absorption behavior of the optical fiber can be determined using reference solutions with defined polysulfide concentrations over a predetermined wavelength range of the incident light. If the calibrated optical fiber is then integrated into a battery cell, the current polysulfide concentration in the battery cell can be deduced from the measured absorption. Chemical reaction processes within the battery cell can thus be investigated in a suitable manner.

[0023] In a favorable battery cell design, the first fiber segment can include a glass rod that allows light to pass out of and / or into the first fiber segment. In particular, the glass rod can be free of any sheathing or coating. A sheathing could be, for example, an opaque plastic tube, as is commonly used with optical fibers. A coating could be a material applied directly to the glass rod. Such a coating could, for example, be a plastic, even a transparent one.

[0024] In this way, a portion of the incident light beam can pass into the active material of the battery cell and interact with it, allowing the current polysulfide concentration to be determined from the absorption of the light beam. However, a suitable coating can also be selected for the glass rod, which enables higher sensitivity of the measuring system. Such a fiber section with a glass rod is also referred to as a coreless fiber.

[0025] According to a favorable embodiment of the battery cell, the glass rod of the first fiber section can have a length between 0.1 mm and 1000 mm, preferably 1 mm and 100 mm, and particularly preferably 5 mm and 40 mm. With such dimensions of the first fiber section, suitable determinations of the polysulfide concentration in metal-sulfur battery cells can be carried out.

[0026] In a favorable embodiment of the battery cell, the at least one optical fiber can comprise a second fiber section with a multimode fiber and a third fiber section with a multimode fiber, wherein the first fiber section is arranged between the second and third fiber sections and optically coupled to them. The second and third fiber sections can be located at least partially outside the cell housing. The light beam can be coupled into and out of the first fiber section in a suitable manner to determine the absorption caused by different polysulfide concentrations. The second and third fiber sections can be routed tightly into and out of the cell housing, allowing the battery cell to operate normally.

[0027] In a favorable embodiment of the battery cell, at least one optical fiber can have a second fiber section with a multimode fiber, wherein the first fiber section is optically coupled to the second fiber section and is mirrored at its free end. The second fiber section can be located at least partially outside the cell housing. In particular, a beam splitter can be connected or connectable to the second fiber section. In this alternative embodiment, only one second fiber section is required to couple the light beam into the first fiber section. The light beam is mirrored at the end of the first fiber section and is also guided out of the battery cell in the same second fiber section.The absorption of the light beam on its way through the first fiber section can thus also be determined, and from this the polysulfide concentration currently present in the battery cell can be deduced.

[0028] According to another aspect of the invention, a metal-sulfur battery with a plurality of metal-sulfur battery cells, in particular pouch cells, with at least one such described battery cell is proposed.

[0029] This allows a metal-sulfur battery to be advantageously designed for use in a real-world application. One or more of the battery cells can be equipped with the sensor device described above, enabling the polysulfide concentrations of one or more battery cells to be analyzed during actual operation of the metal-sulfur battery.

[0030] Metal-sulfur systems can include, for example, lithium-sulfur, magnesium-sulfur, or calcium-sulfur.

[0031] According to a favorable embodiment of the battery, the at least one battery cell can have at least one optical fiber which is calibrated such that the calibrated fiber exhibits a relationship between a wavelength of the incident light beam and an absorption of the light beam in an environment with different concentrations of dissolved sulfur and / or dissolved sulfur compounds.

[0032] The absorption behavior of the optical fiber can be determined using reference solutions with a defined polysulfide concentration over a predefined wavelength range of the incident light. If the calibrated optical fiber is then integrated into a battery cell, the measured absorption can be used to determine the current polysulfide concentration in the battery cell. Chemical reaction processes within the battery cell can thus be investigated in a suitable manner.

[0033] According to a further aspect of the invention, a system for investigating chemical processes in a metal-sulfur battery cell, in particular a pouch cell, is proposed, comprising a sensor device, wherein the sensor device includes at least one optical fiber for transmitting at least one light beam. The at least one optical fiber has at least one first fiber section for light transmission out of and / or into the first fiber section. The at least one optical fiber is arranged at least partially within the cell housing, wherein at least the first fiber section is arranged within the cell housing.

[0034] The system comprises at least one optical transmitter for injecting a light beam into at least one optical fiber of the battery cell, and an optical receiver for receiving a light beam transmitted through the at least one optical fiber. The at least one optical fiber is optically coupled to both the optical transmitter and the optical receiver.

[0035] The proposed system makes it possible to investigate the chemical processes during the operation of a metal-sulfur battery cell using spectroscopy, for example, in the UV-VIS range from 200 nm to 1100 nm. The metal-sulfur battery cell incorporates a sensor device in the form of a first fiber segment, which can be operated as a so-called Fiber Optical Evanescent Wave Sensor (FOEWS). This sensor is designed to transmit light from and / or into the first fiber segment. Particularly in the case of a pouch cell, the optical fiber can be conveniently inserted into the cell housing, in this case the pouch bag, and integrated into an electrode stack without modifying the pouch bag or the electrodes.

[0036] In contrast to operando measurement using conventional optical measuring cells, the pouch cell used in the proposed system requires a very low electrolyte excess, which is very close to an electrolyte / sulfur ratio relevant for the application of at most 5, in particular between at least 3 and at most 5.

[0037] The sensor device is advantageously calibrated with electrolyte and reference solutions containing defined polysulfide solutions. This allows the actual absorption of the sensor device to be determined and a quantitative determination of the polysulfide species to be carried out.

[0038] Metal-sulfur systems can include, for example, lithium-sulfur, magnesium-sulfur, or calcium-sulfur.

[0039] The proposed system allows for the precise investigation of the chemical processes in metal-sulfur batteries. This is possible in principle for all applications where metal-sulfur batteries are used. These can include, for example, aircraft, cars, satellites, spacecraft, ships, trains, or stationary energy storage systems.

[0040] With a favorable system design, the sensor device can be configured as an evanescence wave sensor. The polysulfide concentration can then be determined appropriately using evanescence wave spectroscopy.

[0041] According to a favorable design of the system, at least one optical fiber can be calibrated such that the calibrated fiber exhibits a relationship between a wavelength of the incident light beam and an absorption of the light beam in an environment with different concentrations of dissolved sulfur and / or dissolved sulfur compounds.

[0042] The absorption behavior of the optical fiber can be determined using reference solutions with a defined polysulfide concentration over a predefined wavelength range of the incident light. If the calibrated optical fiber is then integrated into a battery cell, the measured absorption can be used to determine the current polysulfide concentration in the battery cell. Chemical reaction processes within the battery cell can thus be investigated in a suitable manner.

[0043] In a favorable design of the system, the optical transmitter unit can include a light source, in particular a deuterium halogen lamp. A light beam generated with such a light source can be advantageously used for evanescence wave spectroscopy to determine the polysulfide concentration.

[0044] With a favorable system design, the optical receiving unit can be configured as a spectrometer. This allows the absorption of the light beam in the battery cell to be determined as a function of wavelength, enabling a more precise determination of the electrolyte-sulfur ratio than when using a single wavelength.

[0045] With a favorable system design, the optical receiving unit can be coupled with a data processing system. This data processing system can be used for further processing of the measurement data, for example by means of pattern recognition, preferably also using artificial intelligence methods, in order to investigate the chemical processes in the battery cell even more precisely.

[0046] With a favorable design, the system can be configured for spectroscopy in a UV-VIS wavelength range, particularly in the wavelength range from 200 nm to 1100 nm. This allows spectroscopy to be used in both the visible wavelength range of light and up to the ultraviolet, enabling a more precise investigation of the chemical processes within the battery cell.

[0047] In a favorable embodiment of the system, the at least one optical fiber can have a second fiber section with a multimode fiber and a third fiber section with a multimode fiber, wherein the first fiber section is arranged between the second and third fiber sections and is optically coupled to the second and third fiber sections. The optical transmitting unit can be optically coupled to an end of the second fiber section facing away from the first fiber section, and the optical receiving unit can be optically coupled to an end of the third fiber section facing away from the first fiber section. The light beam generated in the optical transmitting unit can thus be coupled into the second fiber section in a suitable manner and thereby transmitted to the first fiber section.The third fiber section allows the light beam, which is partially weakened by absorption, to be coupled from the battery cell into the optical receiving unit.

[0048] In a favorable embodiment of the system, at least one optical fiber can have a second fiber section with a multimode fiber, wherein the first fiber section is optically coupled to the second fiber section and is mirrored at its free end. The second fiber section can be optically coupled at its end opposite the first fiber section to a beam splitter, wherein the optical transmitting unit for coupling the light beam and the optical receiving unit for receiving the reflected light beam are optically coupled to the beam splitter. In this alternative embodiment, the incident light beam and the reflected light beam can be coupled into and out of the first fiber section via the same second fiber section.Outside the battery cell, a beam splitter can be provided to separate the reflected light beam from the transmitted light beam and direct it into the optical receiving unit.

[0049] According to a further aspect of the invention, the use of a calibrated optical fiber in a sensor device for investigating chemical processes in a metal-sulfur battery cell, particularly a pouch cell, is proposed in a system described above. The optical fiber is calibrated such that it exhibits a correlation between the wavelength of the incident light beam and the absorption of the light beam in an environment with varying concentrations of dissolved sulfur and / or dissolved sulfur compounds. The light beam is transmitted by an optical transmitter unit of the system through at least a portion of the cell casing of the battery cell within the optical fiber.After passing at least partially through the cell casing, a light beam is received by an optical receiving unit of the system, whereby at least one intensity of the received light beam is determined.

[0050] This allows for the advantageous investigation of chemical processes during the operation of a metal-sulfur battery cell using spectroscopy, for example in the UV-VIS range from 200 nm to 1100 nm. The metal-sulfur battery cell incorporates a sensor device in the form of a first fiber segment, which can be operated as a so-called fiber optical evanescent wave sensor (FOEWS). Particularly in the case of a pouch cell, the optical fiber can be conveniently inserted into the cell housing, in this case the pouch bag, and integrated into an electrode stack without modifying the pouch bag or the electrodes.

[0051] In contrast to operando measurement using conventional optical measuring cells, the pouch cell used in the proposed system requires a very low electrolyte excess, which is very close to an electrolyte / sulfur ratio relevant for the application of at most 5, in particular between at least 3 and at most 5.

[0052] The sensor device is advantageously calibrated with electrolyte and reference solutions containing defined polysulfide solutions. This allows the actual absorption of the sensor device to be determined and a quantitative determination of the polysulfide species to be carried out.

[0053] If the calibrated optical fiber is then integrated into a battery cell, the measured absorption can be used to determine the current polysulfide concentration in the battery cell. Chemical reaction processes within the battery cell can thus be investigated in a suitable manner.

[0054] Metal-sulfur systems can include, for example, lithium-sulfur, magnesium-sulfur, or calcium-sulfur.

[0055] With a favorable design, the received light beam can be spectrally analyzed. This allows the absorption of the light beam in the battery cell to be determined as a function of wavelength, enabling a more precise determination of the polysulfide concentration than when using a single wavelength.

[0056] With a suitable design, information about the state of the battery cell can be extracted from the signals of the spectral analysis using a data processing system. In particular, the current polysulfide concentration can be reliably determined in this way.

[0057] With a suitable setup, the solubility behavior of sulfur and / or sulfur compounds in a battery cell electrolyte can be determined. This allows, advantageously, the investigation of the so-called polysulfide shuttle in metal-sulfur battery cells.

[0058] A favorable method for investigating chemical processes in a metal-sulfur battery cell, particularly a pouch cell, comprises a sensor device in a system described above. A light beam is transmitted from an optical transmitter unit of the system through at least one calibrated optical fiber, at least partially, through the cell casing of the battery cell. After passing at least partially through the cell casing, the light beam is received by an optical receiver unit of the system, and at least one intensity of the received light beam is determined.

[0059] This allows for the advantageous investigation of chemical processes during the operation of a metal-sulfur battery cell using spectroscopy, for example in the UV-VIS range from 200 nm to 1100 nm. The metal-sulfur battery cell incorporates a sensor device in the form of a first fiber segment, which can be operated as a so-called fiber optical evanescent wave sensor (FOEWS). Particularly in the case of a pouch cell, the optical fiber can be conveniently inserted into the cell housing, in this case the pouch bag, and integrated into an electrode stack without modifying the pouch bag or the electrodes.

[0060] In contrast to operando measurement using conventional optical measuring cells, the pouch cell used in the proposed system requires a very low electrolyte excess, which is very close to an electrolyte / sulfur ratio relevant for the application of at most 5, in particular between at least 3 and at most 5.

[0061] The sensor device is advantageously calibrated with electrolyte and reference solutions containing defined polysulfide solutions. This allows the actual absorption of the sensor device to be determined and a quantitative determination of the polysulfide species to be carried out.

[0062] Metal-sulfur systems can include, for example, lithium-sulfur, magnesium-sulfur, or calcium-sulfur.

[0063] This method allows the received light beam to be spectrally analyzed. This enables the wavelength-dependent determination of the light beam's absorption in the battery cell, allowing the polysulfide concentration to be determined more accurately than when using a single wavelength.

[0064] This method allows information about the state of a battery cell to be extracted from the signals of spectral analysis using a data processing system. In particular, the current polysulfide concentration can be reliably determined in this way.

[0065] The method can be used to determine the solubility behavior of sulfur and / or sulfur compounds in an electrolyte of the battery cell.

[0066] The advantage of metal-sulfur batteries is their high specific energy density. A crucial factor for their practical application is the so-called polysulfide shuttle. The high solubility of sulfur in the liquid system presents an inherent problem that has not yet been solved, particularly for high-energy-density cells, which require a high sulfur content in the cathode. In the proposed metal-sulfur battery cell, fiber optic sensors enable the detection and analysis of this polysulfide shuttle.

[0067] Being able to analyze this solubility behavior of sulfur, also called polysulfide species, in application-relevant cell formats such as pouch cells represents a very large added value for the research and development of metal-sulfur batteries.

[0068] In this method, at least one optical fiber can be calibrated such that the calibrated fiber exhibits a relationship between a wavelength of the incident light beam and an absorption of the light beam in an environment with different concentrations of dissolved sulfur and / or dissolved sulfur compounds.

[0069] If the calibrated optical fiber is then integrated into a battery cell, the measured absorption can be used to determine the current concentration of dissolved sulfur and / or dissolved sulfur compounds in the battery cell. Chemical reaction processes within the battery cell can thus be investigated in a suitable manner. drawing

[0070] Further advantages will become apparent from the following description of the drawings. The figures illustrate exemplary embodiments of the invention. The figures, the description, and the claims contain numerous features in combination. It will be advantageous for those skilled in the art to also consider the features individually and combine them into meaningful further combinations.

[0071] They show, for example: Fig. 1 a system for investigating chemical processes in a metal-sulfur battery cell, in particular a pouch cell, with a sensor device according to an embodiment of the invention; Fig. 2 a schematic structure of a metal-sulfur battery cell, in particular a pouch cell, with a sensor device according to an embodiment of the invention; Fig. 3 a system for investigating chemical processes in a metal-sulfur battery cell, in particular a pouch cell, according to a further embodiment of the invention; Fig. 4 a schematic structure of a metal-sulfur battery cell, in particular a pouch cell, with a sensor device according to a further embodiment of the invention; Fig. 5 Absorption spectra of lithium polysulfides at different concentrations measured in a conventional transmission measurement; Fig. 6 Calibration data of a sensor device of a lithium-sulfur battery cell at different lithium polysulfide concentrations; Fig. 7 Calibration data of sensor devices of different lengths for the largest absorption peak at a wavelength of 220 nm; Fig. 8. Cycling behavior of metal-sulfur pouch cells with integrated sensor device at different electrolyte / sulfur ratios; Fig. 9 a signal from a sensor device of a metal-sulfur battery cell for one charge-discharge cycle; Fig. 10. Development of absorption spectra for a first discharge cycle; and Fig. 11. Development of absorption spectra for a first charging cycle. Embodiments of the invention

[0072] In the figures, similar or equivalent components are numbered with the same reference symbols. The figures merely show examples and are not to be understood as limiting.

[0073] The directional terminology used below, including terms like "left," "right," "above," "below," "in front," "behind," "after," and the like, serves only to improve the understanding of the figures and is in no way intended to limit their generality. The components and elements depicted, their interpretation, and their use may vary according to the considerations of a person skilled in the art and be adapted to the specific applications.

[0074] Fig. Figure 1 shows a system 200 for investigating chemical processes in a metal-sulfur battery cell 100, in particular a pouch cell, with a sensor device 50 according to an embodiment of the invention.

[0075] The metal-sulfur battery cell 100 can, for example, be designed as a pouch cell. In the cell housing 52, in the case of a pouch cell the so-called pouch bag, at least one anode 54 and one cathode 58 are arranged, which are separated by a separator 56.

[0076] In Fig. Figure 2 shows a schematic structure of the metal-sulfur battery cell 100, in particular pouch cell, with the sensor device 50.

[0077] The sensor device 50 comprises an optical fiber 20 for transmitting a light beam 12 and has a first fiber section 21. The first fiber section 21 is configured to allow light to pass out of and / or into the first fiber section 21.

[0078] The optical fiber 20 is arranged at least partially within the cell housing 52. At least the first fiber section 21 is arranged within the cell housing 52.

[0079] The optical fiber 20 has a second fiber section 22 with a multimode fiber 24 and a third fiber section 23 with a multimode fiber 24. The first fiber section 21 is arranged between the second and third fiber sections 22, 23 and is optically coupled to the second and third fiber sections 22, 23.

[0080] The second fiber section 22 is led into the cell housing 52 and the third fiber section 23 is led out of the cell housing 52.

[0081] The first fiber section 21 can, for example, be arranged in the cell housing 52 between the anode 54 and the separator 56. Alternatively, the first fiber section 21 can be arranged as shown in Fig. 2. The first fiber section 21 is identifiable as being arranged between the separator 56 and the cathode 58. In a further alternative embodiment, the first fiber section 21 can also be arranged in the cathode 58, in particular embedded therein.

[0082] As shown in the detailed description in Fig. As can be seen in Figure 2, the fiber section 21 is coupled at coupling points 34 within the anode 54 and cathode 58 with the second fiber section 22 and the third fiber section 23 of the optical fiber 20.

[0083] The in Fig. The system 200 shown in Figure 1 further comprises an optical transmitting unit 10, which feeds a light beam 12 into the optical fiber 20 of the battery cell 100, and an optical receiving unit 30, which receives a light beam 16 transmitted through the optical fiber 20.

[0084] For this purpose, the optical fiber 20 is optically coupled to both the optical transmitting unit 10 and the optical receiving unit 30. The optical transmitting unit 10 is optically coupled to an end of the second fiber section 22 facing away from the first fiber section 21, and the optical receiving unit 30 is optically coupled to an end of the third fiber section 23 facing away from the first fiber section 21.

[0085] The optical transmitting unit 10 has a light source 14, in particular a deuterium halogen lamp, for generating the light beam 12.

[0086] The optical receiving unit 30 can advantageously include a spectrometer 32 and, as shown, be coupled to a data processing system 40.

[0087] The System 200 can thus be advantageously configured for spectroscopy in a UVVIS wavelength range, in particular in a wavelength range from 200 nm to 1100 nm.

[0088] The first fiber section 21 can preferably be configured as an evanescent wave sensor. The evanescent wave field 18, which can propagate radially around the first fiber section 21, is in Fig. 2 schematically indicated.

[0089] The first fiber section 21 can, for example, have a glass rod 26 or be designed as a glass rod 26, which allows light to pass out of and / or into the first fiber section 21, in particular transversely to the longitudinal extent of the fiber section 21. In particular, the first fiber section 21 can be free of a protective sheath or coating. Alternatively, however, a suitable coating may be advantageous for higher sensitivity of the sensor device 50.

[0090] The glass rod 26 of the first fiber section 21 can, for example, have a length 28 between 0.1 mm and 1000 mm, preferably between 1 mm and 100 mm, particularly preferably between 5 mm and 40 mm.

[0091] Fig. Figure 3 represents a system 200 for investigating chemical processes in a metal-sulfur battery cell 100, in particular a pouch cell, according to a further embodiment of the invention.

[0092] In this embodiment, the optical fiber 20, as in the previous embodiment, has a second fiber section 22 with a multimode fiber 24. However, in this embodiment, the first fiber section 21, which is optically coupled to the second fiber section 22, 23, is mirrored at its free end 36, causing the incident light beam 12 to be reflected and guided back out of the first fiber section 21 into the second fiber section 22 as a reflected light beam 16.

[0093] The second fiber section 22 is guided into the cell housing 52 as in the previous embodiment.

[0094] The second fiber section 22 is connected to, or can be connected to, a beam splitter 35.

[0095] Fig. Figure 4 shows the schematic structure of the metal-sulfur battery cell according to Fig. 3 with the sensor device 50 in enlarged view.

[0096] In this embodiment, the first fiber section 21 is embedded in the cathode 58 and mirrored at its free end 36.

[0097] The second fiber section 22 is optically coupled at its end facing away from the first fiber section 21 to a beam splitter 35.

[0098] The optical transmitting unit 10 is optically coupled to the beam splitter 35 via an input fiber 42 for coupling the light beam 12 into the beam splitter 35 and thus into the second fiber section 22. The optical receiving unit 30 is optically coupled to the beam splitter 35 via an output fiber 44 for receiving the reflected light beam 16.

[0099] The optical fiber 20 can be calibrated with its first fiber section 21 such that the calibrated fiber exhibits a relationship between a wavelength 60 of the incident light beam 12 and an absorption 62 of the light beam 12 in an environment with different concentrations 80 of dissolved sulfur and / or dissolved sulfur compounds.

[0100] This includes in Fig. 5 exemplary absorption spectra 62 of lithium polysulfides at different concentrations 84, 85, 86, 87, 88, 89, measured in a conventional transmission measurement, are shown.

[0101] The absorption 62 over the wavelength 60 between 200 nm and 600 nm is shown for different sulfur concentrations 84, 85, 86, 87, 88, 89.

[0102] These are conventional transmission measurements in cuvettes with an optical path length of 0.1 mm. Concentration 84 corresponds to 50 mmol / l (millimoles per liter), concentration 85 to 20 mmol / l, concentration 86 to 10 mmol / l, concentration 87 to 5 mmol / l, concentration 88 to 2 mmol / l, and concentration 89 to 1 mmol / l.

[0103] In Fig. Figure 6 shows calibration data of a sensor device 50 of a lithium-sulfur battery cell 100 at different lithium polysulfide concentrations 81, 82, 83, 84, 85. The length 28 of the first fiber section 21 was 5 mm.

[0104] The electrolyte sulfur concentration 81 corresponds to 500 mmol / l, concentration 82 corresponds to 200 mmol / l, concentration 83 corresponds to 100 mmol / l, concentration 84 corresponds to 50 mmol / l, concentration 85 corresponds to 20 mmol / l.

[0105] In Fig. 7 are calibration data of the absorption 62 of sensor devices 50 of different lengths 28 for the largest absorption peak at a wavelength of 220 nm as a function of the sulfur concentration 80 in mmol / l according to Fig. 6 shown.

[0106] The different lengths 28 of the first fiber section 21 show a linear relationship with the electrolyte sulfur concentration 80. Length 37 corresponds to 40 mm, length 38 to 15 mm, and length 39 to 5 mm.

[0107] In the Fig. Figures 8 to 11 show results of measurements on lithium-sulfur battery cells 100 with a sensor device 50 during operation of the battery cells 100.

[0108] Fig. Figure 8 shows the cycling behavior of metal-sulfur pouch cells 100 with integrated sensor device 50 at different electrolyte / sulfur ratios 91, 92, 93, 94.

[0109] It is shown that with the help of the integrated sensor device 50 measurements can be carried out at significantly lower electrolyte / sulfur ratios 91, 92, 93, 94 than with previous operando pouch cell designs for lithium sulfur battery cells.

[0110] In Fig. 8 represents the capacity of the battery cell (68) in mAh / g over the number of charge / discharge cycles (66). The electrolyte / sulfur ratios correspond to 24 in 91, 12 in 92, 7 in 93, and 5 in 94.

[0111] At the lower electrolyte / sulfur ratios 93, 94, the decrease in capacity 68 of the battery cell 100 appears to be significantly slower than at the higher electrolyte / sulfur ratios 91, 92.

[0112] In Fig. Figure 9 shows a signal from a sensor device 50 of a metal-sulfur battery cell 100 for a discharge / charge cycle. The upper part of the Fig. 9 the potential 90 in V as a function of time 70 in h plotted, while in the lower part of the Fig. 9 shows an absorption 64 relative to the start of the measurement.

[0113] With the sensor device 50 it is apparently possible to detect characteristic signal changes due to changes in the chemical composition of the electrolyte.

[0114] Potential peaks 90, which occur when the battery cell 100 is fully charged, are reflected in significant dips in the relative absorption 64, while a slight potential drop when the battery cell 100 is discharged is shown in a small attenuation in the relative absorption 64.

[0115] This apparently allows a determination of the state of charge based on the measurement with the sensor device 50 in the battery cell 100.

[0116] Fig. Figure 10 shows an evolution of absorption spectra for a first discharge cycle, while Fig. Figure 11 shows the development of absorption spectra for a first charging cycle.

[0117] The absorption 62 is plotted again over the wavelength 60 from 200 to 600 nm. A first fiber section 21 was used as a sensor device 50 with a length 28 of 40 mm.

[0118] The spectral behavior is recognizable at the limit values ​​71 (100% state of charge), 72 (50% state of charge), and 73 (0% state of charge), during the discharge cycle in Fig. 10 characterized by dark areas that remain approximately constant over the entire wavelength range 60.

[0119] In Fig. In Figure 11, in which the charging cycle is shown, the same limit values ​​71, 72, 73 are recognizable.

[0120] However, in both cases, the following aspects stand out clearly: Fig. 10, Fig. 11 characteristic polysulfide peaks 74 especially at high charge states 71, 72 of the battery cell 100.

[0121] A calibrated optical fiber 20 can therefore be used in a sensor device 50 for investigating chemical processes in a metal-sulfur battery cell 100, in particular a pouch cell, in a system 200.

[0122] The optical fiber 20 can be calibrated such that the calibrated fiber exhibits a relationship between a wavelength 60 of the incident light beam 12 and an absorption 62 of the light beam 12 in an environment with different concentrations 80 of dissolved sulfur and / or dissolved sulfur compounds.

[0123] The absorption 62 can be measured by sending a light beam 12 from an optical transmitter 10 of the system 200 through the optical fiber 20 at least partially through a cell housing 52 of the battery cell 100, and by receiving a light beam 16 after passing at least partially through the cell housing 52 by an optical receiver 30 of the system 200. At least one intensity of the received light beam 16 can then be determined.

[0124] The received light beam 16 can be spectrally analyzed. Information about the state of the battery cell 100 can be extracted from the signals of the spectral analysis using a data processing system 40.

[0125] In this way, the solubility behavior of sulfur and / or sulfur compounds in an electrolyte of battery cell 100, the so-called polysulfide shuttle, can be advantageously determined.

[0126] By means of such a method, chemical processes in a metal-sulfur battery cell 100, in particular a pouch cell, can be advantageously investigated with a sensor device 50 in a system 200 described above. Reference sign 10 optical transmitter units 12 transmitted light beam 14 Light source 16 received light beam 18 Evanescence wave field 20 optical fibers 21 first fiber section 22 second fiber section 23 third fiber section 24 multimode fiber 26 glass rods 28 Length 30 optical receiving units 32 spectrometers 34 Coupling point 35 beam splitters 36 mirrored end 37 Length 40 mm 38 Length 15 mm 39 Length 5 mm 40 Data processing system 42 coupling fiber 44 output fiber 50 Sensor device 52 cell casings 54 Anode 56 Separator 58 Cathode 60 wavelength 62 Absorption 64 relative absorption 66 cycle number 68 capacity 70 Time 71 Limit value 100% 72 Limit 50% 73 Limit 0% 74 polysulfide peaks 80 Concentration 81 Concentration 500 mmol / l 82 Concentration 200 mmol / l 83 Concentration 100 mmol / l 84 Concentration 50 mmol / l 85 Concentration 20 mmol / l 86 Concentration 10 mmol / l 87 Concentration 5 mmol / l 88 Concentration 2 mmol / l 89 Concentration 1 mmol / l 90 Potential 91 E / S=24 92 E / S=12 93 E / S=7 94 E / S=5 100 battery cells 200 System

Claims

[1] Metal-sulfur battery cell (100), in particular pouch cell, with a cell housing (52) in which at least one anode (54) and at least one cathode (58) are arranged, which are separated by a separator (56), and with a sensor device (50) for investigating chemical processes in the battery cell (100), wherein the sensor device (100) comprises at least one optical fiber (20) for transmitting at least one light beam (12), wherein the at least one optical fiber (20) has at least one first fiber section (21) for light transmission out of the first fiber section (21) and / or into the first fiber section (21), wherein the at least one optical fiber (20) is arranged at least partially in the cell housing (52), wherein at least the first fiber section (21) is arranged within the cell housing (52). [2] Battery cell according to claim 1, wherein at least the first fiber section (21) is arranged, in particular embedded, in the cell housing (52) between the anode (54) and the separator (56) or between the separator (56) and the cathode (58) or in the cathode (58). [3] Battery cell according to claim 1 or 2, wherein the first fiber section (21) is configured as an evanescent wave sensor. [4] Battery cell according to one of the preceding claims, wherein the at least one optical fiber (20) is calibrated such that the calibrated fiber (20) exhibits a relationship between a wavelength (60) of the incident light beam (12) and an absorption (62) of the light beam (12) in an environment with different concentrations (80) of dissolved sulfur and / or dissolved sulfur compounds. [5] Battery cell according to one of the preceding claims, wherein the first fiber section (21) has a glass rod (26) which allows light to pass out of and / or into the first fiber section (21), in particular free from a sheathing or coating. [6] Battery cell according to one of the preceding claims, wherein the glass rod (26) of the first fiber section (21) has a length (28) between 0.1 mm and 1000 mm, preferably 1 mm and 100 mm, particularly preferably 5 mm and 40 mm. [7] Battery cell according to one of the preceding claims, wherein the at least one optical fiber (20) has a second fiber section (22) with a multimode fiber (24) and a third fiber section (23) with a multimode fiber (24), wherein the first fiber section (21) is arranged between the second and third fiber sections (22, 23) and is optically coupled to the second and third fiber sections (22, 23), wherein the second fiber section (22) and the third fiber section (23) are arranged at least partially outside the cell housing (52). [8] Battery cell according to one of claims 1 to 6, wherein the at least one optical fiber (20) has a second fiber section (22) with a multimode fiber (24), wherein the first fiber section (21) is optically coupled to the second fiber section (22) and is mirrored at its free end (36), wherein the second fiber section (22) is arranged at least partially outside the cell housing (52), in particular wherein a beam splitter (35) is connected or connectable to the second fiber section (22). [9] Metal-sulfur battery with a plurality of metal-sulfur battery cells (100), in particular pouch cells, wherein at least one battery cell (100) is designed according to one of the preceding claims. [10] Battery according to claim 9, wherein the at least one battery cell (100) has at least one optical fiber (20) which is calibrated such that the calibrated fiber (20) exhibits a relationship between a wavelength (60) of the incident light beam (12) and an absorption (62) of the light beam (12) in an environment with different concentrations (80) of dissolved sulfur and / or dissolved sulfur compounds. [11] System (200) for investigating chemical processes in a metal-sulfur battery cell (100), in particular a pouch cell, according to one of claims 1 to 8, with a sensor device (50), wherein the sensor device (50) comprises at least one optical fiber (20) for transmitting at least one light beam (12), wherein the at least one optical fiber (20) has at least one first fiber section (21) for light transmission out of the first fiber section (21) and / or into the first fiber section (21), wherein the at least one optical fiber (20) is arranged at least partially in the cell housing (52), wherein at least the first fiber section (21) is arranged within the cell housing (52), at least comprising an optical transmitting unit (10) for feeding a light beam (12) into at least one optical fiber (20) of the battery cell (100), an optical receiving unit (30) for receiving a light beam (16) transmitted through the at least one optical fiber (20), wherein at least one optical fiber (20) is optically coupled to the optical transmitting unit (10) and the optical receiving unit (30). [12] System according to claim 11, wherein the sensor device (50) is designed as an evanescent wave sensor device. [13] System according to claim 11 or 12, wherein the at least one optical fiber (20) is calibrated such that the calibrated fiber exhibits a relationship between a wavelength (60) of the incident light beam (12) and an absorption (62) of the light beam (12) in an environment with different concentrations (80) of dissolved sulfur and / or dissolved sulfur compounds. [14] System according to one of claims 11 to 13, wherein the optical transmitting unit (10) comprises a light source (14), in particular a deuterium halogen lamp. [15] System according to one of claims 11 to 14, wherein the optical receiving unit (30) is designed as a spectrometer (32). [16] System according to one of claims 11 to 15, wherein the optical receiving unit (30) is coupled to a data processing system (40). [17] System according to one of claims 11 to 16, configured for spectroscopy in a UVVIS wavelength range, in particular in a wavelength range from 200 nm to 1100 nm. [18] System according to any one of claims 11 to 17, wherein the at least one optical fiber (20) has a second fiber section (22) with a multimode fiber (24) and a third fiber section (23) with a multimode fiber (24), wherein the first fiber section (21) is arranged between the second and third fiber sections (22, 23) and is optically coupled to the second and third fiber sections (22, 23), wherein the optical transmitting unit (10) is optically coupled to an end of the second fiber section (22) facing away from the first fiber section (21), and wherein the optical receiving unit (30) is optically coupled to an end of the third fiber section (23) facing away from the first fiber section (21). [19] System according to any one of claims 11 to 17, wherein the at least one optical fiber (20) has a second fiber section (22) with a multimode fiber (24), wherein the first fiber section (21) is optically coupled to the second fiber section (22) and is mirrored at its free end (36), wherein the second fiber section (22) is optically coupled at its end facing away from the first fiber section (21) to a beam splitter (35), wherein the optical transmitting unit (10) for coupling in the light beam (12) and the optical receiving unit (30) for receiving the reflected light beam (16) are optically coupled to the beam splitter (35). [20] Use of a calibrated optical fiber (20) in a sensor device (50) for investigating chemical processes in a metal-sulfur battery cell (100), in particular a pouch cell, according to one of claims 1 to 8, in a system (200) according to one of claims 11 to 19, wherein a calibration of the optical fiber (20) is carried out such that the calibrated fiber exhibits a relationship between a wavelength (60) of the incident light beam (12) and an absorption (62) of the light beam (12) in an environment with different concentrations (80) of dissolved sulfur and / or dissolved sulfur compounds, wherein the light beam (12) is sent from an optical transmitting unit (10) of the system (200) in the optical fiber (20) at least partially through a cell housing (52) of the battery cell (100), wherein a light beam (16) is received by an optical receiving unit (30) of the system (200) after passing at least partially through the cell housing (52), wherein at least one intensity of the received light ray (16) is determined. [21] Use according to claim 20, wherein the received light beam (16) is spectrally analyzed. [22] Use according to claim 21, wherein information on a state of the battery cell (100) is extracted from the signals of the spectral analysis by means of a data processing system (40). [23] Use according to any one of claims 20 to 22, wherein a solubility behavior of sulfur and / or sulfur compounds in an electrolyte of the battery cell (100) is determined.

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