Airtight and heatable cell for FTIR spectroscopic investigation of battery structures

Abstract

The invention relates to an airtight cell for the FTIR spectroscopic investigation of electrochemical electrode and electrolyte processes, wherein the cell has a specific structure with a heating sleeve comprising an electrical heating element.

Description

[0001] The present invention relates to an airtight cell for the FTIR spectroscopic investigation of electrochemical electrode and electrolyte processes, wherein the cell has a specific structure with a heating sleeve comprising an electrical heating element.

[0002] Batteries are important electrical energy storage devices and have become an indispensable part of our daily lives, especially for mobile applications such as laptops, smartphones, and electric mobility in general. The fact that a broader and more marketable range of technical solutions has emerged over time is due to the significant increases in performance and longevity, particularly of rechargeable batteries, over the past few decades. Despite the improvements achieved, a wide variety of charge carrier systems have been and continue to be investigated in order to increase battery performance and reduce costs. A key factor in the functionality of the systems is the reversible charging and discharging of the batteries, which is essentially influenced and determined by the electrochemical processes at the electrodes and in the electrolyte.In this respect, it is important for both application and research to have customized options for the analytical observation of electrode processes. In order to realistically investigate not only liquid electrolytes but also solid electrolytes, polymer electrolytes, gel / solid-liquid electrolytes, or mixtures of these electrolytes, as well as the interfaces and boundary layers formed in batteries, various requirements must be met by the measuring cell. For example, a suitable spectro-electrochemical cell must be airtight, and it should be possible to use a wide variety of electrode and electrolyte materials. To conduct investigations under a wide range of ambient conditions, it would also be desirable if additional environmental and operating parameters could be precisely controlled and influenced easily and cost-effectively.This is important for the investigation of solid electrolytes or polymer electrolytes, since their properties, such as ionic conductivity or viscosity, are only suitable for use in batteries at temperatures above approximately 50°C.

[0003] The patent literature also contains a wide variety of FTIR setups for investigating electrochemical electrode processes.

[0004] For example, JP 2013-124862 A describes an infrared spectroscopy device comprising a working electrode immersed in an electrolyte, a paired electrode paired with the working electrode, a reference electrode indicating a potential of the working electrode, and a prism whose underside is brought into contact with the working electrode. Infrared light is irradiated onto an interface between the prism and the working electrode and reflected at the interface, and the spectrum of the reflected light emitted by the prism 4 is detected by a detector. In this way, the intensity of the total reflected light of the infrared light on the electrode is measured. The prism is made of diamond.

[0005] JP 2012 - 202 951 A1 describes an infrared spectroscopic analysis device that uses an attenuated total reflection (ATR) method. The device includes a total reflection prism having a prism base material and a metal oxide film provided on a bottom surface of the base material; a working electrode arranged on the surface of the material film; a counter electrode paired with the working electrode; a reference electrode defining a potential of the working electrode; and an interface between the base material and the metal oxide film through the prism base material. Infrared spectroscopy includes an optical system that receives infrared light, collects reflected light reflected at the interface and then exits the prism, and an infrared spectrometer for obtaining a spectrum of the reflected light.

[0006] Furthermore, Weiling et al. in Adv. Energy Mater. 2024, 14, 2303568, DOI:10.1002 / aenm.202303568 "Mechanistic Understanding of Additive Reductive Degradation and SEI Formation in High-Voltage NMC811||SiOx-Containing Cells via Operando ATR-FTIR Spectroscopy" disclose a setup for an ATR-FTIR spectroscopic cell.

[0007] JP 2002-277388 A discloses an ATR-type infrared thin-film measuring device, wherein the end face of the attenuated total reflection prism is covered by a thin-film measuring holder provided with an infrared ray through-hole. The measuring device is mounted on the attenuated total reflection prism, which exhibits no absorption in the infrared range, in close contact with the growth thin film of a measurement object, to perform chemical analysis of the growth thin film by directing infrared rays onto the end face of the attenuated total reflection prism.

[0008] Furthermore, WO 2009 / 040 721 A1 discloses a microelectronic sensor device and a method for optically examining a contact surface of a carrier, wherein the carrier has at least one conductor wire. The microelectronic sensor device preferably comprises a light source for emitting an input light beam into the carrier so that it impinges on the contact surface, wherein the conductor wire runs substantially parallel to the plane of incidence of the input light beam. The conductor wire(s) can be used, for example, to generate magnetic fields or for local heating. The described aligned alignment of the conductor wire(s) and the input light beam achieves minimal disturbance (shadowing) of the input light beam.

[0009] Against this background of the prior art, the object of the invention is therefore to provide an improved structure for an ATR-FTIR spectroscopic cell. In particular, the device according to the invention is intended to enable simple and uniform temperature control of the electrode and electrolyte structure to be examined.

[0010] This object of the invention is achieved with a cell having the features specified in claim 1. Preferred developments of the invention are specified in the associated subclaims, the following description, and the drawings.

[0011] According to the invention, a cell for the ATR-FTIR spectroscopic investigation of electrochemical electrode and electrolyte processes is provided, wherein the cell comprises, starting from a lower support surface for an FTIR spectrometer up to an upper end of the cell: a working electrode current collector configured for electrically contacting a working electrode, a receiving space suitable for receiving an electrode assembly comprising a working electrode, an electrolyte and a counter electrode;and above the receiving space, a first counterelectrode current collector configured for electrically contacting the counterelectrode of the electrode assembly, wherein the first counterelectrode current collector mechanically and electrically contacts a second counterelectrode current collector via a spring element, wherein a heating sleeve comprising an electrical heating element contacts at least a partial surface area of ​​the first counterelectrode current collector in a thermally conductive connection;

[0012] Surprisingly, it was discovered that the cell structure described above allows for cost-effective, reliable, and highly precise cell and thus electrode and electrolyte temperature control, significantly expanding the cell's application spectrum. Electrode and electrolyte reactions can be monitored under varying temperature conditions. Furthermore, investigations into the influence of cyclic temperature changes on the electrode and electrolyte processes of different electrode materials are also possible. This structure is advantageous compared to existing cell structures because, although existing cells are airtight and, in individual cases, allow the investigation of a wide variety of electrode materials, these structures lack the capability of precise temperature control. In the structure according to the invention, the heating element integrated into the cell can be controlled by means of a control unit, thus altering the cell temperature.Another advantage of the present setup is that, in addition to examining the electrode interface, the overlying electrolyte can also be examined simultaneously. The setup is specifically aimed at investigating interfaces or layers, whereby a wide variety of electrode materials can be incorporated for the electrodes. This is significantly more advantageous than using electrodes permanently installed in the cell, which are then naturally limited to the installed electrode material. The latter is particularly relevant because gold electrodes are used in known setups. However, gold electrodes do not correspond to the actual electrodes in battery cells. Therefore, these cells cannot be used to examine battery-relevant electrodes. Further advantages of the new cell arise from its easy adaptability and a significantly lower price, since the cell is, in principle, 3D-printable.In addition, liquid, solid and hybrid electrolytes can be investigated.

[0013] The cell is suitable for the ATR-FTIR spectroscopic investigation of electrochemical electrode and electrolyte processes. The cell is designed to be mounted on an ATR crystal of an FTIR spectrometer. The cell therefore does not contain any structures for conducting FTIR measurements, but "only" provides the sample chamber, which can be filled with various electrode and electrolyte structures. ATR infrared spectroscopy ("attenuated total reflection") is a measurement technique within infrared spectroscopy (IR spectroscopy) that enables the surface investigation of solid or liquid samples by investigating the system's interaction with light of a specific wavelength spectrum. By analyzing the intensity of backscattered or reflected light, conclusions can be drawn about the chemical composition and properties of the sample.The cell can be manufactured, for example, using SLA printing from Composite-X (Liqcreate). An alternative 3D printing method would be SLS, which can use PP or FDM. Less preferred, ablative manufacturing methods such as turning or milling can also be used to produce the housing. The cell can easily be made airtight, for example, using seals. This cell allows electrochemical processes to be monitored at different electrodes and in different electrolytes.

[0014] The cell extends from a lower support surface to an FTIR spectrometer and ends at the top of the cell. The cell is thus attached to the ATR crystal, and the light used for the analysis is directed from below through the ATR crystal into the cell. The sequence of the individual housing components described below is therefore arranged from the bottom, the cell base, possibly in contact with an ATR crystal, to the top, the cell end.

[0015] The cell comprises a working electrode current collector configured for electrically contacting a working electrode. To investigate the electrode processes of an electrode assembly, the cell is equipped with a working electrode current collector, which, when an electrode assembly to be investigated is installed, is capable of transmitting electrical signals from the working electrode or to the working electrode. To fulfill this purpose, when the cell is assembled with an installed electrode, the working electrode current collector makes electrical contact with the electrode. The working electrode current collector can be made of copper, nickel, stainless steel, or aluminum, for example, and can be designed in the form of a flat disc. The flat disc can contain a hole in the center into which the working electrode can be placed.The working electrode current collector preferably has an external electrical contact point at which the electrical signals can be tapped. The working electrode current collector is arranged directly below the receiving space for an electrode assembly.

[0016] The cell comprises a receiving chamber suitable for accommodating an electrode assembly comprising a working electrode, an electrolyte, and a counter electrode. The cell can accommodate the electrode assembly to be tested. This takes place in the receiving chamber, into which the assembly to be tested is installed. The electrode assembly comprises at least a lower working electrode and an upper counter electrode, which are separated by an electrolyte. Depending on the assembly, the electrolyte can be solid, liquid, or gel-like. Different metals can be used for the current collectors of the working and counter electrodes. In particular, the structure and chemical composition of the electrode assembly to be tested are not limited by the properties and basic design of the cell. When testing liquid electrolytes, the installation of seals may be necessary or advantageous.

[0017] The cell comprises a first counterelectrode current collector located above the receiving space, designed to electrically contact the counterelectrode of the electrode assembly. To detect or adjust the electrical properties of the electrode assembly, the counterelectrode of the electrode assembly is contacted via the cell by a counterelectrode current collector. This current collector, together with the working electrode current collector, enables electrical contact with the electrode assembly. The counterelectrode current collector can preferably be made of copper, nickel, stainless steel, or aluminum and have a thickness of greater than or equal to 5 mm and less than or equal to 25 mm.

[0018] The first counterelectrode current collector contacts a second counterelectrode current collector mechanically and electrically via a spring element. A conductive connection via a first and a second counterelectrode current collector is used to conduct the electrical signals from the counterelectrode. The first and second counterelectrode current collectors are connected by a spring element, which, in addition to making electrical contact, is also responsible for the mechanical contact of the entire electrode and electrolyte structure. Mechanical forces are exerted on the first counterelectrode current collector and thus on the electrode and electrolyte structure via the spring element, which contributes to good electrical contact between the individual parts. Furthermore, the structure can also be sealed using this contact pressure. Suitable spring elements include spiral springs, wave springs, or conical springs.Suitable spring constants of the spring elements can be, for example, greater than or equal to 100 N / m and less than or equal to 50000 N / m.

[0019] The cell comprises a heating sleeve having an electrical heating element that contacts at least a partial surface area of ​​the first counterelectrode current collector in a thermally conductive connection. A heating sleeve is arranged inside the cell, which ultimately enables the temperature control of the electrode structure via thermal contact with at least the counterelectrode current collector. The heating sleeve can, of course, also comprise further parts of the structure. The heating sleeve is enclosed by the cell housing and, according to the invention, is not arranged on the outside of the cell. This can enable improved heat conduction. An electrical heating element can preferably be used as the heating element. The heating element can preferably be connected by one or more electrical lines to a heating control system that is configured to control the temperature of the heating element.The heating element can, for example, be configured to achieve a temperature in a range from 20°C to 500°C. Preferably, the heating element can occupy a volume of 10% to 50% of the volume of the heating sleeve. The heating sleeve can, for example, enclose the heating element on three sides or entirely.

[0020] In a further preferred embodiment of the cell, the first counterelectrode current collector can be cylindrical, and the heating sleeve can contact at least 70% of the outer surface of the first counterelectrode current collector. For improved thermal contacting of the first counterelectrode current collector, it has proven particularly advantageous for at least a large portion of the outer surface of the first counterelectrode current collector to be encompassed by the heating sleeve. Rapid temperature changes can be initiated, and the temperature distribution at the first counterelectrode current collector is very uniform. In this case, a cylindrical design means that the first counterelectrode current collector has a round base. The height of the first counterelectrode current collector is greater than the diameter of the base.Preferably, the heating sleeve can thermally contact greater than or equal to 80% and less than or equal to 100%, and furthermore greater than or equal to 90% and less than or equal to 100%, of the outer surface area of ​​the first counterelectrode current collector. The outer surface area results from the cylindrical surface area minus the area of ​​the round base surfaces.

[0021] In a preferred characteristic of the cell, the receiving space can be cylindrical and the heating sleeve can encompass at least 70% of the outer surface of the receiving space. For improved thermal contact with the receiving space, it has proven particularly advantageous for at least a large part of the outer surface of the receiving space to be encompassed by the heating sleeve. Rapid temperature changes can be initiated and the temperature distribution in the receiving space is very uniform. A cylindrical design in this case means that the receiving space has a round base area. The height of the receiving space is greater than the diameter of the base area. The heating sleeve can preferably thermally contact greater than or equal to 80% and less than or equal to 100%, furthermore greater than or equal to 90% and less than or equal to 100%, of the outer surface of the receiving space.Preferably, the heating sleeve can contact the specified surface areas of the first counter electrode current collector and the receiving space.

[0022] In a further preferred characteristic of the cell, the heating sleeve can be configured to accommodate a temperature sensor. For improved control of the temperature of the receiving space, it has proven advantageous for a temperature sensor to be integrated into the heating sleeve. For this purpose, the heating sleeve can, for example, have a bore or hole. Preferably, the bore can be greater than or equal to 1 mm and less than or equal to 30 mm from the heating device. It has proven advantageous for the heating device not to be arranged too close to the temperature sensor. This can increase the reproducibility of the temperature control and regulation as well as possible heating and cooling ramps. The heating sleeve can accommodate the temperature sensor, for example, by means of a mechanical clamp. However, it is also possible for the temperature sensor to be glued into the heating sleeve using a thermal paste.Alternatively or additionally, the thermal sensor can be fixed in the heating sleeve with one or more (grub) screws.

[0023] In a preferred embodiment of the cell, the electrical heating element can be an electrical resistance heater. The use of a resistance heater has proven particularly suitable for the most efficient and flexible temperature control of the electrode and electrolyte structure. The cell can be temperature-controlled particularly precisely over wide temperature ranges. The resistance heater can preferably have a power of greater than or equal to 20 W and less than or equal to 200 W. The resistance heater can preferably have a length of greater than or equal to 5 mm to less than or equal to 30 mm and a diameter of greater than or equal to 2 mm to less than or equal to 15 mm. The resistance heater can preferably maintain the temperature in the range greater than or equal to 0°C to less than or equal to 500°C.

[0024] In a further preferred embodiment of the cell, the first counterelectrode current collector can consist of greater than or equal to 80 wt.% and less than or equal to 100 wt.% copper, wherein at least the contact surface of the first counterelectrode current collector with the spring element can have a gold coating. For the most efficient thermal and electrical contact possible, it has proven particularly suitable for the first counterelectrode current collector to consist predominantly of copper and additionally have a gold coating. The gold coating is applied to the surface that contacts the spring element. Preferably, only this surface can have a gold coating. The gold coating can, for example, have a thickness of 0.5 - 100 µm.

[0025] In a further preferred embodiment of the cell, the first counterelectrode current collector can be cylindrical and have a minimum extension in the direction of the cylinder axis of greater than or equal to 4 times and less than or equal to 10 times the maximum extension of the receiving space. It has proven very suitable for the first counterelectrode current collector to have a height in the range specified above. Within this height range, reliable mechanical, electrical, and thermal contact with the receiving space can be achieved. Furthermore, the mass of the first counterelectrode current collector provided in this size range can provide a sufficient thermal reservoir, which prevents major temperature fluctuations in the receiving space.

[0026] In a preferred characteristic of the cell, the electrical heating element can consist of greater than or equal to 80 wt.% and less than or equal to 100 wt.% copper and can be coated on the surface, wherein the coating is selected from the group consisting of AlN, Al2O3, BN, mica, or mixtures of at least two compounds from this list. To electrically insulate the heating element and reduce electrical interference, it has proven advantageous to apply an insulating coating to the surface of the heating element. Contrary to the assumption of the person skilled in the art, this only insignificantly reduces the thermal properties but increases the electrical interference immunity of the structure.

[0027] In a further preferred embodiment of the cell, the heating sleeve can be electrically decoupled from the working electrode current collector. To reduce electrical interference, it has also proven advantageous for the heating sleeve to be electrically decoupled from the working electrode current collector. This can be achieved, for example, by a non-conductive coating on the surface of the heating sleeve. Suitable examples of non-conductive coatings are given above. Furthermore, it can be advantageous for the electrically non-conductive coating to have a preferably good thermal conductivity. For this purpose, the coating can consist of mica, for example. The electrically non-conductive coating preferably has a thermal conductivity of greater than or equal to 100 W m -1 K -1Preferably, the coating has a thickness of greater than or equal to 0.1 mm and less than or equal to 5 mm. Instead of or in addition to a coating, a thermally conductive and electrically non-conductive layer or plate, e.g., made of mica, can be placed between the heating sleeve and the working electrode current collector. Alternatively, both parts can be electrically and thermally decoupled from each other by an O-ring made of rubber, Teflon, PEEK, or similar.

[0028] In a preferred embodiment of the cell, the spring element can consist of greater than or equal to 80 wt.% and less than or equal to 100 wt.% stainless steel and have a gold coating on the surface. For particularly suitable electrical and mechanical contact, it has proven advantageous for the spring element to be predominantly made of stainless steel, with the spring element having a gold coating on its surface. Preferably, the spring element can be made of stainless steel in addition to the surface coating.

[0029] In a further preferred embodiment of the cell, the second counterelectrode current collector can consist of stainless steel of greater than or equal to 80 wt.% and less than or equal to 100 wt.%. Optionally, the second counterelectrode current collector can also be provided with a gold coating. Within these compositions, electrically highly suitable second counterelectrode current collectors can be obtained, which, for example, exhibit lower heat dissipation than copper current collectors. The temperature control of the cell structure is thereby improved.

[0030] Furthermore, a cell may be advantageous, wherein the cell is configured so that the position of the second counterelectrode current collector can be mechanically fixed within the cell. The second counterelectrode current collector can be fixed, for example, by means of an adjusting ring.

[0031] Furthermore, the invention provides for the use of the cell according to the invention for investigating electrode structures comprising at least one electrode and an electrolyte contacting the electrode surface.

[0032] Examples and embodiments of the present invention will be described by way of example with reference to the Fig. 1 to 3 described: Fig. 1 shows schematically the structure of an ATR-FTIR cell according to the invention Fig. 2A-D schematically show a heating element usable according to the invention in different views; Fig. 3A-D schematically show a cell housing usable according to the invention in different views.

[0033] The Fig. 1 shows a schematic cross-sectional view of the structure of a cell 100 according to the invention. The cell 100 is arranged on an IR crystal / prism 1, which has a holder for an IR crystal 2. From bottom to top, the cell 100 contains a working electrode 3 with a working electrode current collector 4. This part of the cell 100 can be sealed from the environment by means of sealing rings 5, 9. The holder space contains an electrolyte 6, a working electrode 3, and a counter electrode 7. This holder space is contacted or enclosed by the heating sleeve 8, which has a heating element 13, for example in the form of an electrical resistance heater. The heating sleeve 8 can fix the individual functional parts using grub screws 10. Optionally, a temperature sensor 12 can also be arranged in the heating sleeve 8.A first counterelectrode current collector 11 extends through the heating sleeve 8 and contacts a second counterelectrode current collector 18 via a spring element 16. This part of the cell 100 can be sealed by a gasket 17 and mechanically secured by an Allen screw 15. The cell 100 is terminated by the screw connection 19, which ensures the mechanical cohesion of the entire cell structure 100. The electrical contact of the heating element 13 and the optionally usable thermocouple 12 are not shown in this figure. For the sake of clarity, the possible installation of a reference electrode has also not been shown.

[0034] The Fig. 2A-D show different views of the heating sleeve 8, with a large hole for the first counter electrode current collector 11, a middle hole for a heating element 13, for example in the form of an electrical resistance heater, and a small hole for the temperature sensor 12. Four further small threaded holes are shown for fastening the heating element 13 and the temperature sensor with grub screws 10.

[0035] The Fig.3A-D show the cell housing 14 in different views. The cell housing 14 can have a large bore at the bottom for the heating sleeve 8 and a central bore for the spring element 16 and the second counter electrode current collector 18. Furthermore, additional bores for the passage of Allen screws 15 and two bores for the cable feedthroughs of the heating element 13 and an optional temperature sensor 12 can be provided. In these cases, the reference numerals indicate the bores for the corresponding functional parts and not the parts themselves.

Claims

[1] An airtight cell (100) for the ATR-FTIR spectroscopic investigation of electrochemical electrode and electrolyte processes, wherein the cell (100), starting from a lower support surface to an FTIR spectrometer up to an upper end of the cell (100), comprises: a working electrode current collector (4) configured for electrically contacting a working electrode (3), a receiving space suitable for receiving an electrode assembly comprising a working electrode (3), an electrolyte (6), and a counterelectrode (7); and above the receiving space, a first counterelectrode current collector (11) configured for electrically contacting the counterelectrode (7) of the electrode assembly, wherein the first counterelectrode current collector (11) mechanically and electrically contacts a second counterelectrode current collector (18) via a spring element (16), characterized bythat a heating sleeve (8) comprising an electrical heating element (13) contacts at least a partial surface area of ​​the first counter electrode current collector (11) in a thermally conductive connection. [2] Cell (100) according to claim 1, wherein the first counter electrode current collector (11) is cylindrical and the heating sleeve (8) contacts at least 70% of the outer surface of the first counter electrode current collector (11). [3] Cell (100) according to one of the preceding claims, wherein the receiving space is cylindrical and the heating sleeve (8) comprises at least 70% of the outer surface of the receiving space. [4] Cell (100) according to one of the preceding claims, wherein the heating sleeve (8) is adapted to receive a thermal sensor (12). [5] Cell (100) according to one of the preceding claims, wherein the electrical heating element (13) is an electrical resistance heater. [6] Cell (100) according to one of the preceding claims, wherein the first counter-electrode current collector (11) consists of greater than or equal to 80 wt.% and less than or equal to 100 wt.% copper, wherein at least the contact surface of the first counter-electrode current collector (11) to the spring element (16) has a gold coating. [7] Cell (100) according to one of the preceding claims, wherein the first counter-electrode current collector (11) is cylindrical and has a minimum extension in the direction of the cylinder axis of greater than or equal to 4 times and less than or equal to 10 times the maximum extension of the receiving space. [8] Cell (100) according to one of the preceding claims, wherein the electrical heating element (13) consists of greater than or equal to 80 wt.% and less than or equal to 100 wt.% copper and is coated on the surface, wherein the coating is selected from the group consisting of AlN, Al2O3, BN, mica or mixtures of at least two compounds from this list. [9] Cell (100) according to one of the preceding claims, wherein the heating sleeve (8) is electrically decoupled from the working electrode current collector (4). [10] Cell (100) according to one of the preceding claims, wherein the spring element (16) consists of greater than or equal to 80 wt.% and less than or equal to 100 wt.% stainless steel and has a gold coating on the surface.

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