NMR measuring head for in operando measurements on a battery

Abstract

NMR measuring head (2) for performing NMR measurements on a battery (1), comprising i) a measuring station (15) for a battery (1), comprising a first contacting element (K1) and a second contacting element (K2) for a first electrode (E1) and a second electrode (E2) of the battery (1), ii) a tuning capacity (30), iii) a first RF connection (H1) and a second RF connection (H2) for an NMR console (6), wherein the contact elements (K1, K2) are conductively connected for RF current via the tuning capacitance (30), so that an RF resonant circuit (3) can be set up with a battery (1) to be arranged at the measuring station (15), and wherein the first RF terminal (H1) is conductively connected to the first contact element (K1) and the second RF terminal (H2) is conductively connected to the second contact element (K2), iv) a first DC terminal (D1) and a second DC terminal (D2) for a DC current element (4), and v) at least a first block element (B1) which is permeable to DC current and blocking to RF current at least in the range of a provided resonant frequency REF of the RF resonant circuit (3), The first DC terminal (D1) is conductively connected to the first contact element (K1) via the first block element (B1), and the second DC terminal (D2) is conductively connected to the second contact element (K2) for DC current. The NMR probe enables simple, operando NMR measurements on a battery with high signal strength.

Description

[0001] The invention relates to an NMR measuring head for performing NMR measurements on a battery.

[0002] Such an NMR measuring head is known, for example, from US 11 215 686 B2.

[0003] Nuclear magnetic resonance (NMR) spectroscopy can be used to analyze the chemical composition of samples. For this purpose, a sample is exposed to a homogeneous static magnetic field (“B0 field,” constant over time) of a background magnet (often a superconducting background magnet), and radio frequency (RF) pulses (“B1 field,” time-varying) are directed perpendicular to the static magnetic field into the sample and interact with the nuclear spins of the atoms and molecules in the sample. A resulting RF signal from the sample is measured, and the composition of the sample can be determined from the measurement result.

[0004] In a typical MMR setup used in chemical analysis, the sample is positioned in an NMR probe head (also called an NMR sample head) which includes an RF resonator or an RF coil, with the RF resonator or coil surrounding the sample. The NMR probe head protrudes into a magnetic bore of the background magnet.

[0005] In recent years, the importance of technical applications requiring batteries has increased. Here, "batteries" encompasses all types of electrochemically based electrical energy storage devices; batteries include both non-rechargeable batteries (also known as primary batteries) and rechargeable batteries (also known as accumulators or secondary batteries). Technical applications requiring batteries include, for example, watches (including smartwatches), hearing aids, flashlights, mobile phones and tablets, and even motor vehicles.

[0006] For battery research and development, including the optimization of energy density, charging efficiency, and battery lifespan, investigating the electrochemical processes within batteries is of great interest. Particular attention is paid to the electrochemical processes during charging and discharging. The information content of solid-state NMR is very high compared to other spectroscopic techniques, so that in many cases it is not necessary to combine it with other analytical methods.

[0007] Batteries are typically housed in metallic casings. If such a battery is placed in an RF resonator or coil, the RF pulses and signals cannot penetrate the metallic casing, or only to a very limited extent. Consequently, only very low signal strengths can be achieved in an NMR measurement.

[0008] To circumvent this problem, it has become known to arrange the internal electrochemical structure of the battery under investigation in an electromagnetically transparent container (usually made of plastic). The corresponding plastic battery cell can then be placed inside an RF resonator or an RF coil. The company ePROBE GmbH, Erfurt, Germany, offers suitable NMR probes and associated plastic containers commercially; see [reference]. https: / / eprobe.tech / products / probes (downloaded on December 6, 2024) and https: / / eprobe.tech / products / cells (downloaded on December 6, 2024). The ePROBE probe head comprises a solenoid coil as an RF coil, into which a cylindrical plastic container is inserted. This container, in turn, holds the electrochemical setup under investigation. While this approach enables highly efficient NMR measurements of the electrochemical setup, including in-operando investigations (i.e., during charging and discharging), the electrochemical processes in the plastic battery cell are not identical to those in the original battery, which has a metallic casing.

[0009] In US 11 215 686 B2, also published as US 2021 / 0318401 A1, it is proposed to arrange a button cell with a metallic casing inside a hairpin resonator, with the high-frequency oscillating magnetic fields aligned tangentially to the electrodes of the button cell. The button cell is electrically isolated from the hairpin resonator. In a variant for in-operando NMR, it is proposed to connect the electrodes of the battery cell to DC wire conductors for charging and discharging, with the DC wire conductors not touching the resonator, and RF chokes to keep high frequencies away from the DC terminals. With this setup, some penetration of the RF fields into the button cell through its insulation gap is achieved, but the NMR performance is still relatively low. A similar approach is also described by Brennan J. Walder et al. in “NMR spectroscopy of coin cell batteries with metal casing” Sci. Adv 2021; 7: eabg8298, September 10, 2021.The only difference compared to commercially available button cells and standard button cells used in battery research is that the casing is made of titanium.

[0010] In S. Benders et al., “Nuclear magnetic resonance spectroscopy of rechargeable pouch cell batteries: beating the skin depth by excitation and detection via the casing”, Sci. Rep. (2020) 10: 13781, pp. 1-7, it is proposed to attach a copper tape to each of the outer surfaces of a pouch cell and connect them to the RF terminals of an NMR spectrometer. The two copper tapes are also connected to each other via a tuning capacitor, thus establishing an RF resonant circuit. A matching capacitor is connected in series with the RF resonant circuit. The electrode terminals of the pouch cell are galvanically isolated from the copper tapes. Before integrating the pouch cell into the RF resonant circuit, several charge / discharge cycles at 300 mA were performed. A similar procedure is described in US 2022 / 0003824 A1.

[0011] Furthermore, US patent 2018 / 0053973 A1 has revealed the possibility of integrating a stripline resonator into a battery or fuel cell. This allows for NMR measurements with a high signal-to-noise ratio. However, this approach does not allow for direct measurement of an original battery. Additionally, the stripline resonator can alter the electrochemical processes within the battery.

[0012] DE 10 2022 131 403 A1 discloses a method for performing NMR measurements on batteries. For this purpose, the battery is integrated into a resonant circuit of the NMR probe head. Pulsed NMR measurements are performed, in which a spin resonance signal is generated and recorded by at least one radio frequency pulse. Object of the invention

[0013] The object of the invention is to provide an NMR measuring head with which NMR measurements on a battery with a high signal strength can be easily performed in operando. Description of the invention

[0014] This problem is solved according to the invention by an NMR measuring head for carrying out NMR measurements on a battery, comprehensive i) a measuring station for a battery, comprising a first contact element for a first electrode of the battery and a second contact element for a second electrode of the battery, ii) a tuning capacity, and iii) a first RF connection and a second RF connection for an NMR console, wherein the first contact element and the second contact element are conductively connected for RF current via the tuning capacitance, so that an RF resonant circuit can be set up with a battery to be arranged at the measuring station, and wherein the first RF terminal is conductively connected to the first contact element for RF current and the second RF terminal is conductively connected to the second contact element for RF current, iv) a first DC terminal and a second DC terminal for a DC power element, and v) at least a first blocking element which is permeable to DC current and blocking to RF current at least in the range of a specified resonant frequency REF of the RF resonant circuit, wherein the first DC terminal is conductively connected to the first contact element via the first block element, and the second DC terminal is conductively connected to the second contact element for DC current, where at least one first block element ensures that the RF resonant circuit is not affected by the DC current element.

[0015] The invention provides for the establishment of an RF resonant circuit into which the battery to be measured is directly integrated. For this purpose, the two contact elements in the NMR measuring head, which contact the battery's electrodes when the battery is inserted, are conductively connected to each other via the tuning capacitance for RF current. The NMR measurement can then be performed in an NMR spectrometer using this RF resonant circuit.

[0016] The RF connections, to which the NMR console of the NMR spectrometer is connected, are conductively connected to the contact elements for RF current. This makes the battery electrodes accessible to RF pulses, and RF signals from the battery can be read out.

[0017] The battery can be considered a resonator. The opposing electrodes with the intervening electrolyte layer represent a capacitance, with the electrolyte layer contributing to relatively high losses in the RF range. Furthermore, the metallic elements of the battery provide inductance and resistance. The battery's resonant frequency depends strongly on its construction and size and is typically in the range of 10 MHz to 10 GHz.

[0018] By connecting the electrodes or contact elements via the tuning capacitor, the battery's resonant frequency can be changed and, in particular, adjusted to a measurement frequency of the NMR spectrometer. Note that, if desired, additional electrical elements (impedance elements) can be connected in series with the tuning capacitor in the electrical connection of the electrodes. The tuning capacitor can be a single component or multiple components, for example, with a first partial tuning capacitor and a second partial tuning capacitor connected in series. In practice, the tuning capacitor or partial tuning capacitors can be implemented by a single capacitor or several capacitors connected in parallel. The tuning capacitor blocks DC current in the electrode connection, thus preventing a DC short circuit of the battery electrodes via the RF side.

[0019] To enable NMR measurements during operation (i.e., NMR measurements while charging or discharging the battery), the NMR probe also includes DC connections to a DC current element. At least the first DC connection is conductively connected to the first contact element via a first blocking element. This first blocking element allows DC current to pass through but blocks RF current, at least within a predetermined frequency range corresponding to the resonant frequency (REF) of the RF resonant circuit. The second DC connection is conductively connected to the second contact element, allowing DC current to pass through.If desired, the second DC terminal can be connected to the second contact element via a second block element, wherein the second block element is permeable to DC current but blocks RF current at least in the region of the resonant frequency REF of the RF resonant circuit (see below); a second block element is not required if the second contact element is grounded; in this case, the second DC terminal can be directly electrically connected to the second contact element.

[0020] The DC current element, connected to the DC terminals, allows the battery to be charged or discharged during an ongoing NMR measurement. The associated DC current is not affected by the blocking element(s) (apart from the inherent series resistance of each blocking element). However, the blocking element(s) filter out (block) RF currents at least at and near the resonant frequency of the RF resonant circuit or at or near the measurement frequency of the NMR measurement. The blocking element(s) thus ensures that the DC current element does not affect the RF resonant circuit and, in particular, does not cause any interference (especially no additional noise) in the NMR measurement.Furthermore, it is also ensured that the DC current element is not affected or damaged by RF currents from the NMR measurement (especially when RF pulses are injected into the battery).

[0021] The batteries to be measured can be of conventional design within the scope of the invention, in particular with metallic housings. In particular, it is not necessary to insert resonators into the battery.

[0022] Within the scope of the invention, a high NMR signal strength can be achieved because RF pulses can be introduced directly into the interior of the battery via the electrically contacted electrodes of the battery itself, and RF signals from the battery can be registered with the battery's electrodes themselves. No penetration of external electromagnetic fields into the battery through a housing is necessary. Accordingly, within the scope of the invention, the housing of the battery under investigation can be metallic. Preferably, the metallic electrodes of the battery substantially completely overlap the cross-section of the battery from opposite sides.

[0023] According to the invention, the two contact elements (or the two battery electrodes) are electrically connected to both the NMR console (or the RF source for the NMR measurement) via the RF terminals and to the DC current element via the DC terminals. RF current is blocked relative to the DC current element by at least one blocking element. In addition, DC current is typically also blocked relative to the RF source by a blocking capacitor (see below). According to the invention, a DC current and an RF current can be applied simultaneously to the battery electrodes, and NMR measurements can therefore be performed concurrently.

[0024] If desired, the NMR measurement frequency and, consequently, the resonant frequency of the RF resonant circuit can also be variable, for example, via a variable tuning capacitance. The invention can also be adapted accordingly for multi-core circuits with multiple resonant frequencies REFi can be used (with i: index of the cores under investigation). Separate RF connections may be provided for the different measurement frequencies. The blocking element(s) then block RF current at least at each of the resonant frequencies REF. i . Preferred embodiments of the invention

[0025] In a preferred embodiment, the measuring station is configured for a battery designed as a button cell. Button cells allow for the simple adjustment of the self-resonance (in the fundamental mode) to the measurement frequency of the NMR measurement using the tuning capacitance. Since the self-resonance of this battery type is higher than the usual NMR measurement frequencies, and no higher self-resonance mode with at least one current within the battery needs to be used for the measurement, homogeneous current distributions across the conductor elements within the battery can be achieved. However, it is also possible to use the invention with other battery types, in particular pouch cells or cylindrical cells; optionally, a higher self-resonance mode can then be tuned to the measurement frequency using the tuning capacitance, although this will impair the field homogeneity of the generated B1 field.

[0026] In one embodiment, the second RF connection is particularly preferred, as it is connected to ground. This simplifies the overall design of the NMR probe.

[0027] In a preferred embodiment, the tuning capacitor is configured with a first partial tuning capacitor and a second partial tuning capacitor, wherein the first partial tuning capacitor and the second partial tuning capacitor are connected in series in the RF resonant circuit, and a center tap between the first partial tuning capacitor and the second partial tuning capacitor is connected to ground. This simplifies the process of maintaining (approximate) electrical symmetry in the RF resonant circuit (i.e., symmetrical potentials between the electrodes or between the contact elements during measurement operation) and thus minimizes power losses during the transmission of RF pulses in the battery and received noise from the battery.

[0028] An advantageous embodiment is one in which the second contacting element is connected to ground. In this case, a second block element is generally unnecessary, and a particularly simple electrical design of the NMR measuring head is achieved.

[0029] In another advantageous embodiment, the NMR measuring head further comprises - A second block element, which is conductive for DC current and blocking for RF current, at least in the region of the intended resonant frequency REF of the RF resonant circuit, with the second DC connection being conductively connected to the second contact element via the second block element. In this design, the DC current element can be "floating" and does not need to be grounded, i.e., the DC current can be connected differentially. This allows for the partial suppression of external noise coupled in common-mode.

[0030] A preferred embodiment includes one or more impedance matching elements in the NMR measuring head. This allows the NMR measuring head to be matched to the impedance of the NMR transmitting and receiving electronics in the NMR console. The entirety of the impedance matching elements is also referred to as an impedance matching network. The impedance matching element(s) can, for example, include capacitors, inductors, transformers, and / or coaxial cables of variable impedance and length.

[0031] A preferred embodiment includes a further development in which one of the RF connections, particularly the first RF connection, is connected to its associated contact element via a matching capacitor. The matching capacitor can then serve a dual purpose: firstly, it contributes to impedance matching, and secondly, it blocks DC current from the battery or DC current source, thus preventing the NMR measurement electronics in the NMR console from being affected or damaged by DC current or the resulting voltage.

[0032] A further preferred configuration provides that the tuning capacitance and the impedance matching element(s) are connected in such a way that at least approximately symmetrical potentials are maintained at the two contact elements during measurement operation. In particular, the first RF connection is conductively connected to the first contact element for RF current via a matching capacitance, and the second contact element is conductively connected to ground for RF current via a balancing capacitance, with the matching capacitance and the balancing capacitance having at least approximately the same capacitance value. Such an approximately symmetrical design of the impedance matching network minimizes power losses and interference. Losses in the battery, which provides the relevant inductance for losses in the RF resonant circuit and is connected to the contact elements, are proportional to the square of the electric field strength.By using an (approximately) symmetrical circuit, the loss-causing electric field strength can be (approximately) halved compared to a completely asymmetrical circuit (which is achieved by connecting one electrode of the battery to ground). Remaining asymmetries typically result from matching circuit sides in the NMR probe to ground and 50 ohms. The design with a matching capacitor and a balancing capacitor is relatively easy to implement and allows for a "floating" DC current element (without contact to ground). Approximately equal capacitance values ​​for the matching and balancing capacitors are typically achieved when the capacitance values ​​differ by a maximum of 20%, relative to the smaller capacitance value. In the case of high resonator Q factors, the differences can be significantly smaller, for example, less than 2%, relative to the smaller capacitance value.The same applies to other impedance matching configurations. Another impedance matching configuration to obtain approximately symmetrical potentials at the contact elements involves a tuning capacitor consisting of a first and a second partial tuning capacitor. The first and second partial tuning capacitors are connected in series in the RF resonant circuit, and a center tap between the first and second partial tuning capacitors is connected to ground. The first and second partial tuning capacitors have approximately equal capacitance values ​​(see also above). This configuration with a first and second partial tuning capacitor is also relatively easy to implement and allows for a "floating" DC current element (without contact to ground).

[0033] A preferred embodiment includes at least one of the RF terminals connected to its associated contact element via a DC blocking capacitor. The DC blocking capacitor blocks direct current. This ensures that no direct current (from the battery or the DC current source) is fed into an NMR console connected to the RF terminals or into an RF source located therein. The DC blocking capacitor can be part of an impedance matching network (see above).

[0034] In a preferred embodiment, each block element is configured as a low-pass filter. This design provides a high attenuation effect within a defined frequency range. The low-pass filter is typically configured for defined impedances at the filter's input / output.

[0035] A preferred embodiment incorporates a low-pass filter inductor. This is particularly easy to implement. The (serial) low-pass filter inductor can prevent a short circuit of the RF resonant circuit to ground when a leakage capacitance is used. In particular, the low-pass filter can consist solely of the low-pass filter inductor.

[0036] Another, advantageous sub-variant of the above training program provides for the following: that an inductance value L TPF the low-pass filter inductance is greater than an inductance value L Batt the battery in the RF resonant circuit, in particular where L TPF ≥ 1 nH or 1 nH ≤ L TPF ≤ 50 uH or 100 nH ≤ L TPF ≤ 25 uH. If L TPF >L BattGenerally, good filtering can be achieved in the relevant frequency range. With high values ​​for L TPF High frequencies can be blocked very efficiently. Note that real components for setting up high inductances often have significant parasitic capacitances, which should be taken into account when designing the circuit, for example by using an inductor whose self-resonance (including its parasitic capacitance and, if applicable, its ohmic resistance) is higher than the resonant frequency REF of the RF resonant circuit.

[0037] A sub-variant that provides for is still preferred. that a leakage capacitor is connected between each block element and its associated DC connection, which leads to ground, and that a respective series resonant frequency, which belongs to a series connection of the low-pass filtered inductance of the respective block element with the associated leakage capacitance, is significantly smaller than the intended resonant frequency REF of the RF resonant circuit, In particular, by at least a factor of 5 smaller, preferably by at least a factor of 10 smaller, and most preferably by at least a factor of 50 smaller. Waves (RF current) that still pass through the RF block (block element) can thereby be guided to ground, and an improved blocking effect is achieved. This setup is non-resonant and therefore broadband. Note that comparatively large low-pass filter inductors are typically used in this setup, e.g., with L TPF ≥ 1 nH or even L TPF ≥ 100 nH.

[0038] One preferred sub-variant provides for, that a leakage capacitor is connected between each block element and its associated DC connection, which leads to ground, and that a respective series resonant frequency, belonging to a series connection of the low-pass filter inductance of the respective block element with the associated leakage capacitance, corresponds at least approximately to the intended resonant frequency REF of the RF resonant circuit. With this setup, a high blocking effect at a specific frequency can be achieved, so that the resonant frequency REF, in particular, can be efficiently blocked. The blocking effect for the RF current is achieved here primarily through resonance of the resonant circuit (from the series connection of the low-pass inductance and the leakage capacitance, connected to ground), and only to a lesser extent through the low-pass filter effect of the low-pass filter inductance itself; the leakage capacitance can therefore also be considered functionally as part of the block element.In this sub-variant, low-pass filter inductors with a smaller inductance value can also be used, especially smaller than in the previous sub-variant, e.g. with L. TPF < 1 nH. Filter losses are adjustable via the inductance value of the low-pass filter inductor. Note that in the case of two block elements, their series resonant frequencies (SR1, SR2) are typically chosen with a certain deviation from each other to avoid resonance splitting. In this case, for example, one series resonant frequency is at REF, and the other series resonant frequency deviates slightly from REF. Typically, the series resonant frequencies (SR1, SR2) each deviate by a maximum of 10% from REF (relative to REF).

[0039] An advantageous embodiment is one in which each block element is designed as a notch filter, with the notch filter being blocking in the region of the intended resonant frequency REF of the RF resonant circuit. This design allows independent adjustment of the circuit's symmetry, particularly via an impedance matching element (balancing impedance ZS), which is connected to ground from the second contact element (optionally via a second tuning capacitor). The notch filter is generally formed by a parallel resonant circuit consisting of a notch filter inductor and a notch filter capacitance. The inductance value L Sperr The inductance of the resonant circuit is typically chosen to be larger than an inductance value L. Batt the battery, in order to maintain a low impact on the efficiency of the resonant circuit at REF while ensuring good blocking effect of the filter.

[0040] A preferred embodiment of the NMR measuring head provides for, that a battery holder is available with which the battery can be fixed at the measuring station, so that when the battery is arranged in the battery holder, the first contact element contacts the first electrode of the battery and the second contact element contacts the second electrode of the battery, in particular wherein the battery can be elastically clamped in the battery holder by means of the first contact element and / or the second contact element, that the first contact element and the second contact element are galvanically isolated from each other, and that the first contacting element and the second contacting element are connected to each other by at least one capacitor. The battery holder facilitates handling the battery during measurement and replacement in the NMR probe. Furthermore, this design allows for easy adjustment of the tuning capacity.

[0041] An advantageous further development of this embodiment involves connecting the first and second contact elements to each other via two capacitors, particularly on opposite sides of the battery holder. This allows for a particularly homogeneous RF field distribution within the battery.

[0042] The present invention also includes an NMR spectrometer system comprising - an NMR measuring head according to the invention, as described above, - an NMR console connected to the RF ports, - a DC current element that is connected to the DC terminals, - one or more control units for the NMR console and the DC current element, in particular comprising a control PC, - and a magnet for generating a static magnetic field at the measuring station for the battery, in particular wherein the magnet comprises a shim system. With the NMR spectrometer system according to the invention, NMR-

[0043] Measurements on a battery can be performed at the NMR probe's measuring station. An NMR measurement can therefore take place simultaneously with charging or discharging the battery. The NMR measurements are easy to perform, and a high signal strength or signal-to-noise ratio is achievable. The NMR measurements provide spectrometric information that can be used to elucidate the electrochemical processes within the battery.

[0044] In a preferred embodiment of the NMR spectrometer system according to the invention, the DC current element is a DC charger or a DC discharger. With a DC charger or DC discharger, electrical energy (corresponding to a specific current) can be supplied to or drawn from the battery in a controlled and defined manner. Preferably, the current and / or voltage during charging / discharging are flexibly adjustable electronically. Alternatively, a regulated or unregulated electrical load can simply be connected for discharging.

[0045] The present invention further encompasses an NMR measurement setup comprising an NMR spectrometer system according to the invention as described above and a battery arranged at the measurement station for the battery, wherein a first electrode of the battery is contacted with the first contact element, and a second electrode of the battery is contacted with the second contact element. The measurement setup allows for the simple investigation of the electrochemical behavior of the battery during charging and discharging using high-signal NMR measurements. The battery can be rechargeable or non-rechargeable (in the latter case, only discharge is possible during NMR measurement). The battery can, in particular, have a metallic housing. Preferably, the battery housing is made of a non-magnetic material, especially preferably a non-magnetic metallic material (e.g.,(made of titanium), since a magnetic casing can impair the homogeneity of the static magnetic field during an NMR measurement. Note that, within the scope of the invention, the non-magnetic material of the battery casing can be selected such that no significant electrochemical differences arise compared to a mass-produced battery (e.g., with a steel casing), thus enabling the creation of near-series prototypes for battery research, which can then be measured according to the invention. Apart from the casing material, the battery to be measured requires no special preparation (such as electrodes arranged inside the battery); rather, a conventional battery design, corresponding to a commercially available battery, can be used within the scope of the invention.

[0046] Finally, the invention also includes the use of an NMR measurement arrangement according to the invention, described above, while simultaneously - the battery is charged or discharged using the DC current element, - and an NMR measurement is performed on the battery using the NMR console and the NMR measuring head. This allows high-quality information about the electrochemical behavior of the battery to be easily obtained directly during the charging or discharging process.

[0047] Further advantages of the invention will become apparent from the description and the drawing. Likewise, the features mentioned above and those described in more detail below can each be used individually or in any combination according to the invention. The embodiments shown and described are not to be understood as an exhaustive list, but rather serve as examples for illustrating the invention. Detailed description of the invention and drawing Fig. Figure 1 schematically shows a simple equivalent circuit diagram of a battery, for measurement within the scope of the invention; Fig. Figure 2 schematically shows a circuit diagram of a first, simple embodiment of an NMR measuring head according to the invention, wherein the second RF connection and the second contacting element are connected to ground; Fig. Figure 3 schematically shows a circuit diagram of a further embodiment of an NMR measuring head according to the invention, with a matching capacity; Fig. Figure 4 schematically shows a circuit diagram of a further embodiment of an NMR measuring head according to the invention, with a matching capacitance and a matching inductance; Fig. Figure 5 schematically shows a circuit diagram of another embodiment of an NMR measuring head according to the invention, with a general impedance matching network; Fig. Figure 6 schematically shows a circuit diagram of a further embodiment of an NMR measuring head according to the invention, with two block elements and a symmetrical impedance matching network; Fig. Figure 7 schematically shows a circuit diagram of a first sub-variant of the embodiment of Fig. 6, wherein the block elements are designed with low-pass filter inductors; Fig. Figure 8 schematically shows a circuit diagram of a second sub-variant of the embodiment of Fig. 6, wherein leakage capacitors are connected between the low-pass filter inductors and the DC terminals; Fig. Figure 9 schematically shows a circuit diagram of a third sub-variant of the embodiment of Fig. 6, wherein the block elements are designed as blocking circuits; Fig. 10 a circuit diagram of a further embodiment of an NMR measuring head according to the invention, with two block elements and a two-part tuning capacitor with a center tap that is connected to ground; Fig. 11 a schematic perspective view of an exemplary battery holder for the invention; Fig. 12 a schematic perspective view of an exemplary embodiment of an NMR measuring system according to the invention.

[0048] The Fig. Figure 1 shows a simple equivalent circuit diagram of a battery 1, which is to be subjected to an NMR measurement within the scope of the invention. The battery 1 can, for example, be constructed as a button cell.

[0049] Battery 1 has a first electrode E1 and a second electrode E2. In the case of a button cell, for example, the positive electrode of battery 1 can be designed as a metallic cup, and the negative electrode as a metallic cap. The two electrodes E1 and E2 do not touch inside battery 1 but are electrically separated by an insulating layer (not shown in the circuit diagram). The interior of battery 1 contains an electrochemical structure, typically based on an electrolyte, which essentially stores the electrical energy. The two electrodes are connected to each other within the battery via this electrochemical structure. In the equivalent circuit diagram, C represents Batt The value of the capacitance between electrodes E1 and E2 across the electrolyte or an associated electrolyte layer. R electrolyterepresents the value of the ohmic resistance (as a measure of resistive losses) across the electrolyte layer. Finally, L represents Batt the value of the battery's inductance, determined primarily by its metallic elements (especially the electrodes), and R metal the value of the ohmic resistance (as a measure of resistive losses) across the metallic elements of battery 1.

[0050] Battery 1 thus represents a simple RF resonator. The self-resonance of battery 1 depends on its design and size. By adding capacity, the self-resonance of battery 1 (or the resulting overall circuit) can be tuned to a frequency to be measured (see, for example, in...). Fig. 2).

[0051] The Fig. Figure 2 schematically shows a circuit diagram of an NMR measuring head 2 (also called NMR probe head) for the invention in a first, simple embodiment.

[0052] Battery 1 contacts a first contact element K1 of the NMR measuring head 2 with its first electrode E1, and a second contact element K2 with its second electrode E2. The contact elements K1 and K2 are connected via a tuning capacitance 30 (with capacitance value C). T ) are electrically connected to each other. Via the tuning capacitance 30, the contact elements K1 and K2 are thus conductively connected to each other for RF current; however, DC current is blocked in this current path by the tuning capacitance 30.

[0053] A high-frequency resonant circuit 3 (shown with a dashed outline) is established by the battery 1 and the tuning capacitance 30. The resonant frequency REF of the high-frequency resonant circuit 3 is adjusted by means of the tuning capacitance 30 so that it corresponds to a desired frequency (irradiated by an NMR console) for the NMR measurement. The tuning capacitance 30 can be adjustable, i.e., it can have an adjustable capacitance value C. Texhibit, in particular to adapt to different types of batteries 1 to be measured.

[0054] A first RF connection H1 is directly connected to the first contact element K1 (and thus to the first electrode E1). A second RF connection H2 is also directly connected to the second contact element K2. Both the second RF connection H2 and the second contact element K2 are grounded.

[0055] The RF connections H1 and H2 allow for the use of the connected NMR console (not shown, but see e.g. Fig. 3) of an NMR spectrometer, an NMR measurement is performed on battery 1, where battery 1 is directly integrated into the RF resonant circuit 3. Note that the RF electronics in the connected NMR console should be designed such that no (parallel) current path for DC current is established through them (unless a blockage for DC current is already ensured by other components in the NMR probe head 2, e.g., by a series DC blocking capacitor, see e.g. in Fig. 3) In addition, the RF electronics in the connected NMR console should be protected against voltages from the charging management (i.e. from the DC current element 4) (unless protection is already provided by other components in the NMR probe head 2).

[0056] A first block element B1 is connected to the first contact element K1. The first contact element K1 is connected to a first DC terminal D1 via the first block element B1. A DC current element 4 is connected to this first DC terminal D1 and to another DC terminal D2. The DC current element 4 is a DC charger 5; alternatively, the DC current element 4 can also be a DC discharger (the latter not shown in detail). The first block element B1 is conductive for DC current. However, the first block element B1 blocks RF current, at least in the region of the resonant frequency REF of the RF resonant circuit 3. In general, the first block element B1 attenuates RF current at frequency REF by at least a factor of 10, preferably at least a factor of 100, and most preferably at least a factor of 1000. The second DC terminal D2 is connected to ground.The second DC terminal D2 is therefore also connected to the second contact element K2 (and thus to the second electrode E2) via ground, in particular conductive for DC current.

[0057] The DC current element 4 can be integrated into the NMR measuring head 2, or it can be separate from the NMR measuring head 2. The DC terminals D1 and D2 connected to the DC current element 4 are part of the NMR measuring head 2.

[0058] Due to the first block element B1, no high-frequency interference from the DC terminals D1, D2, or from the DC current element 4 can affect the NMR measurement (which takes place at the resonant frequency REF of the RF resonant circuit 3). Conversely, no RF current from the NMR measurement can affect or damage the DC current element 4, and the efficiency in both transmission and reception can be optimized.

[0059] Fig. Figure 3 shows a further embodiment of an NMR measuring head 2 according to the invention. Only the essential differences to the design of Fig. 2 explained.

[0060] The NMR probe 2 is shown connected to an NMR console 6, which can transmit RF pulses to the RF resonant circuit 3 (or to battery 1) and also receive RF signals from the RF resonant circuit 3 (or from battery 1). The NMR console 6 is connected to the first RF terminal H1 and to the second RF terminal H2. The second RF terminal H2 is grounded and thus connected to the second contact element K2.

[0061] The first RF connection H1 is connected here via a matching capacitance 31 (with capacitance value C). M) is electrically connected to the first contacting element K1. The matching capacitance 31 fulfills two functions here. Firstly, it serves to match the impedance of the RF resonant circuit 3 (or the entire assembly consisting of the RF resonant circuit 3 and the matching capacitance 31), typically to 50 ohms (corresponding to the impedance in the NMR console 6), at least at the measurement frequency REF. Correct matching maximizes the electromagnetic energy radiated into the battery 1 and minimizes reflections. The matching capacitance 31 thus represents an impedance matching element 7. Furthermore, with correct design of the preamplifier, the signal-to-noise ratio is maximized in the receive case.

[0062] Secondly, the matching capacitance 31 also blocks DC current from the first contact element K1 (and thus from battery 1 and DC current element 4) to the first RF connection H1. The matching capacitance 31 therefore also represents a DC blocking capacitance 8 for direct current. Accordingly, the NMR console 6 cannot be affected by direct current, and the direct current flowing at battery 1 is determined solely by the DC current element 4.

[0063] Fig. Figure 4 shows a further embodiment of an NMR measuring head 2 according to the invention. Only the essential differences to the design of Fig. 3 explained.

[0064] In the embodiment shown, in addition to the matching capacitance 31, a matching inductance 32 (with inductance value L) is also provided. M) provided. The matching inductor 32 is connected here between the first RF connection H1 and the matching capacitor 31. The other end of the matching inductor 32 is connected to ground.

[0065] The Machting capacitor 31 and the matching inductor 32 are each impedance matching elements 7. Together they form an impedance matching network, which sets the impedance of the RF resonant circuit 3 (or the combined impedance of the RF resonant circuit 3 and the impedance matching network). The advantage of this circuit is that the impedance matching can be performed independently of the frequency matching of the RF resonant circuit 3.

[0066] The Fig. Figure 5 shows a further embodiment of an NMR measuring head 2 according to the invention, to illustrate the general possibilities for setting up an impedance matching network. Only the essential differences to the Fig. 3 explained.

[0067] The RF resonant circuit 3 is formed here by the battery 1, whose electrodes E1, E2 are connected via a first partial tuning impedance 33 (with impedance value Z). T1 ) and a second partial tuning impedance 34 (with impedance value Z) T2 ) are connected in a conductive manner for RF current. The first partial tuning impedance 33 and the second partial tuning impedance 34 are connected in series. One of the partial tuning impedances 33, 34, or both partial tuning impedances 33, 34 together, form the tuning capacitance of the RF resonant circuit 3. At least one of the partial tuning impedances 33, 34 contains a series capacitor (not shown in detail), so that a parallel path to the battery 1 for DC current between the contact elements K1, K2 is blocked.

[0068] The first RF connection H1 is via the first matching impedance 35 (with impedance value Z) M1) is conductively connected to the first contacting element K1 for RF current. Typically, the first matching impedance 35 contains a series capacitor that acts as a DC blocking capacitance.

[0069] Between the first RF connection H1 and the first matching impedance 35 there is a second matching impedance 36 (with impedance value Z). M2 ) connected. The second Machting impedance 36 is connected to ground at the other end.

[0070] A balancing impedance 37 (with impedance value Z) is connected at a center tap 8 between the partial tuning impedances 33, 34. S ) connected. The balancing impedance 37 is connected to ground at the other end.

[0071] The first contact element K2 is connected to the first DC terminal D1 via the first block element B1 (see above). The second contact element K2 is connected to the second DC terminal D2 via a second block element B2. The second block element B2 is conductive for direct current but blocks RF current at least in the region of the resonant frequency REF of the RF resonant circuit 3. In general, the second block element B2 attenuates RF current at frequency REF by at least a factor of 10, preferably at least a factor of 100, and most preferably at least a factor of 1000.

[0072] Note that in the case of Z T2 =0 and Z S =0 the second contact element K2 is grounded, and then the second block element B2 is not needed (not shown in detail, but see e.g. Fig. 3 (see below).

[0073] The general design of the NMR measuring head 2 of Fig. 5 can be assigned to the previously presented construction types as follows: In the design of Fig. 2 became Z T1 =C T selected, and all other impedances were set to zero. In the design of Fig. 3 were Z T1 =C T and Z M1 =C M selected, and all other impedances were set to zero. In the design of Fig. 4 were Z T1 =C T and Z M1 =C M and Z M2 =L M selected, and all other impedances were set to zero.

[0074] It should be noted here that the in Fig. The impedance matching networks shown in Figures 5 and the other figures are merely examples, and other prior art alternatives can also be used within the scope of the invention.

[0075] Fig. Figure 6 shows a further embodiment of an NMR measuring head 2 according to the invention. Only the essential features and differences from the design of Fig. 5 explained.

[0076] In this embodiment, the tuning capacity is 30 (with a capacity value of C). T ) formed in one piece, which connects the contact elements K1, K2 together and thereby sets up the RF resonant circuit 3 with the battery 1.

[0077] It is still a matching capacitance 31 (with inductance value C). M ) provided, which connects the first RF terminal H1 to the first contacting element K1 in a conductive manner for RF current.

[0078] Furthermore, a symmetrization capacity of 38 (with capacity value C) is available. S) provided, which connects the second contact element K2 to ground. Note that the second RF connection H2 is also connected to ground here, so the balancing capacitance 38 connects the second contact element K2 to the second RF connection H2. The balancing capacitance 38 also contributes to the matching process.

[0079] The matching capacity 31 and the symmetrization capacity 38 are given here with (approximately) the same capacity values ​​C. M , C S selected, thereby obtaining electrical symmetry at the contacting elements K1 and K2 by creating a virtual ground in the middle of the tuning capacitance 30 through the impedance matching elements 7.

[0080] In the nomenclature of Fig. 5 are in the embodiment of Fig. 6 here Z T1 =C T and Z M1 =C M and Z S =C S chosen, and all other impedances are chosen to be zero.

[0081] The Fig. Figure 7 shows a first sub-variant of the embodiment of the NMR measuring head of Fig. 6; only the essential deviations and special features are explained.

[0082] In this first sub-variant, block elements B1 and B2 are each configured as low-pass filters 9. Here, the low-pass filters 9 are each simply connected by a low-pass filter inductor 39 (with inductance value L). TPF trained. Note that L applies. TPF > L Batt , in order to achieve good filtering effect for RF current without significantly affecting the resonator current.

[0083] The Fig. Figure 8 shows a second sub-variant of the embodiment of the NMR measuring head of Fig. 6; only the essential deviations and special features are explained.

[0084] In this second sub-variant, the block elements B1, B2 are each again designed as a low-pass filter 9, which in turn are each connected by a low-pass filter inductance 39 (with inductance values ​​L TPF B1 , L TPF B2 are trained. Note that L applies. TPF B1 > L Batt and L TPF B2 >L Batt .

[0085] Furthermore, a leakage capacitance 40 (with capacitance value C) is located between the first block element B1 or the associated low-pass filter inductance 39 and the first DC terminal D1. Abl B1 ) connected. The leakage capacitance 40 is connected to ground at the other end.

[0086] Furthermore, a leakage capacitance 40 (with capacitance value C) is located between the second block element B2 or the associated low-pass filter inductance 39 and the second DC terminal D2. Abl B2) connected. The leakage capacitance 40 is connected to ground at the other end.

[0087] The series connection of the low-pass filter inductance 39 of the first block element B1 and the associated leakage capacitance 40 can be assigned a series resonant frequency SR1: SR1=12πLTPFB1∗CAblB1

[0088] Furthermore, a series resonant frequency SR2 can be assigned to the series connection of the low-pass filter inductance 39 of the second block element B2 and the associated leakage capacitance 40: SR2=12πLTPFB2∗CAblB2

[0089] The sub-variant as in Fig. Figure 8 can be used in two different applications.

[0090] In the first application (“non-resonant variant”), SR1 and SR2 are each chosen to be significantly smaller than REF. For this purpose, low-pass filter inductors 39 with comparatively high inductance values ​​L are typically used. TPFB1 , L TPF B2 chosen. By means of a high impedance through a high ω*L TPF B1 or ω*L TPF B2 (where ω denotes the angular frequency of the NMR measurement), achieved through a large inductance value, results in high reflection of the RF waves at the low-pass filter inductor 39. The leakage capacitance 40 then diverts the portions of the RF wave that still pass through the low-pass filter inductor 39 to ground, thus improving the blocking effect. The first application is broadband blocking. In the case described here where SR1 and SR2 << REF, SR1 and SR2 can be either identical or different.

[0091] In the second application (“resonant variant”), SR1 and SR2 each correspond at least approximately to the resonant frequency REF of the RF resonant circuit 3. This second variant is based on a “ground-to-resonant circuit,” meaning that a virtual ground connection is generated for a specific frequency (i.e., the series resonant frequency SR1, SR2). Via the respective leakage capacitance 40, together with the associated low-pass filter inductance 39, RF current in the region of the frequency REF, originating from the contact elements K1, K2, can be leaked to ground with very low resistance and thus kept away from the DC terminals D1, D2. This second application can be described as narrowband blocking. In the case described here, where SR1 and SR2 approximately correspond to the REF, they are preferably chosen to be different from each other in order to avoid resonance splitting.Typically, SR1 and SR2 each deviate from REF by a maximum of 10% (relative to REF).

[0092] The Fig. Figure 9 shows a third sub-variant of the embodiment of the NMR measuring head of Fig. 6; only the essential deviations and special features are explained.

[0093] In this third sub-variant, the block elements B1 and B2 are each configured as resonant circuits 11. Each resonant circuit 11 is formed by a resonant circuit inductance 41 (with inductance value L). Sp ) and a resonant circuit capacity of 42 (with capacity value C) Sp ), which are connected in parallel to each other (parallel resonant circuit). L applies. Sp > L Batt .

[0094] Each retard circuit 11 has a retard frequency SPF with SPF=12πLSp∗CSp where SPF is set (at least approximately) equal to the resonant frequency REF of the RF resonant circuit 3. Accordingly, the blocking circuit 11 blocks RF current at frequency REF. Consequently, no RF current at frequency REF passes through the blocking elements B1, B2. RF pulses from the NMR console 6 and RF signals from the battery 1 do not reach the DC terminals D1, D2. Conversely, no high-frequency interference currents that might be present at the DC terminals D1, D2 can reach the contacting elements K1, K2.

[0095] Fig. Figure 10 shows a further embodiment of an NMR measuring head 2 according to the invention. Only the essential differences to the design of Fig. 5 explained.

[0096] In this embodiment, the tuning capacity 30 is designed in two parts, with the first part tuning capacity 43 (with capacity value C) T1 ) and a second partial tuning capacity 44 (with capacity value C) T2The first partial tuning capacitor 43 and the second partial tuning capacitor 44 are connected in series and connect the first contact element K1 to the second contact element K2 in a conducting manner for RF current, but blocking for DC current; this establishes the RF resonant circuit 3 which contains the battery 1.

[0097] Impedance matching is achieved here via the matching capacitance 31 (with capacitance value C). M ), which simultaneously acts as a DC blocking capacitance 8, blocking direct current.

[0098] Ground is connected at the center tap 8 between the partial tuning capacitors 43 and 44. The typical capacitor values ​​are C. T1 , C T2 The partial tuning capacities 43, 44 are approximately equal (typically with a difference of a maximum of 20%, based on the larger value).

[0099] In the nomenclature of Fig. 5 are in the embodiment of Fig. 10 here Z T1 =CT1 and Z T2 =C T2 and Z M1 =C M chosen, and all other impedances are chosen to be zero.

[0100] The Fig. Figure 11 shows, by way of example, a perspective view of a battery holder 10 which can be integrated into an NMR measuring head according to the invention.

[0101] The battery holder 10 contains a battery 1, which here is designed as a button cell 12. In the illustrated design, the battery holder 10 comprises a metallic base 13 and a metallic bracket 14, which together enclose a measuring position 15 on which the battery 1 is arranged.

[0102] In the present case, two springs 16 are formed in the metallic bracket 14, which are pre-tensioned towards the base 13. The two metallic springs 16 press against the top of the battery 1. The battery 1 is thus elastically clamped in the battery holder 10 by the springs 16; this fixes the battery 1 to the measuring station 15.

[0103] The upper side of battery 1, which forms its first electrode E1, contacts the springs 16 and thus the bracket 14. The lower side of battery 1, which forms its second electrode E2, rests against the base 13. Therefore, in the illustrated configuration, the bracket 14 can be considered the first contact element K1, and the base 13 the second contact element K2. The base 13 and the bracket 14 are galvanically isolated from each other.

[0104] In the illustrated configuration, however, the base 13 and the bracket 14 are connected to each other via both capacitor 45 and capacitor 46. Capacitors 45 and 46 thus form a parallel circuit, which together establishes the tuning capacitance 30; the capacitance values ​​of capacitors 45 and 46 add up to the total capacitance value C. T the tuning capacity 30. The two capacitors 45, 46 are arranged on opposite sides, here opposite lateral sides, of the battery holder 10.

[0105] In the Fig. Figure 12 schematically shows an NMR spectrometer system 20 according to the invention in an exemplary embodiment.

[0106] The NMR spectrometer system 20 comprises an NMR measuring head 2, at the (here upper) end of which the measuring station 15 (shown with a dashed line) for the battery 1 is located. The NMR measuring head 2 is inserted from below into the room temperature bore 22 of a cryostat 21. The measuring station 15 is accordingly located within the room temperature bore 22 of the cryostat 21. A superconducting magnet coil 23 is arranged in the cryostat 21, which generates a static magnetic field in the area of ​​the measuring station 15. In addition, a shim system 24 is provided, which homogenizes the magnetic field in the area of ​​the measuring station 15. The shim system 24 is inserted from above into the room temperature bore 22. The superconducting magnet coil 23 and the shim system 24 together form the magnet 25 (also called background magnet) of the NMR spectrometer system 20.

[0107] The NMR probe 2 is connected to an NMR console 6 via its RF connections. RF pulses can be injected into the NMR probe 2 using the NMR console 6, and RF signals can be read out of the NMR probe 2.

[0108] Furthermore, a battery controller 26 is provided. The battery controller 26 controls a DC current element 4, which can provide charging and / or discharging currents for the battery 1. In the illustrated embodiment, the battery controller 26 and the DC current element 4 can be used to selectively set and change either a charging or a discharging current for the battery 1 at the measuring station 15. In the illustrated embodiment, the DC current element 4 is integrated into the battery controller 26, and the integrated DC current element 4 is connected to the NMR measuring head 2 via the DC terminals. However, it is also possible, for example, to integrate the DC current element into the NMR measuring head (not shown in detail).

[0109] The NMR console 6 and the battery controller 26 are connected to a control PC 27, which allows for the overall monitoring and control of the NMR measurement on battery 1. It is also possible to integrate the battery controller into the control PC (not shown in detail).

[0110] The NMR spectrometer system 20 and a battery arranged at the measuring station 15 together form an NMR measuring arrangement 28 according to the invention, with which NMR measurements can be carried out on the battery 1 while the battery 1 is being discharged or charged at the same time. Reference symbol list 1 battery 2 NMR measuring head 3 HF resonant circuit 4 DC current element 5 DC charger 6 NMR console 7 Impedance matching element 8 DC blocking capacity 9 low-pass filters 10 Battery holder 11 restricted area 12 button cell 13 metallic floor 14 metallic brackets 15 measuring station 16 metallic springs 20 NMR spectrometer system 21 Cryostat 22 Room temperature bore 23 superconducting magnetic coil 24 shim system 25 Magnet 26 Battery control 27 control PCs 28 NMR measurement setup 30 Tuning capacity 31 Matching capacity 32 Matching inductance 33 First partial tuning impedance 34 second partial tuning impedance 35 first matching impedance 36 second matching impedance 37 Balancing Impedance 38 Symmetrization capacity 39 Low-pass filter inductance 40 Discharge capacity 41 Blocking circuit inductance 42 Blocking circuit capacity 43 first partial tuning capacity 44 second part tuning capacity 45 Capacitor 46 Capacitor B1 first block element B2 second block element C Batt Battery capacity C M Capacity value of the matching capacity C S Capacity value of the symmetrization capacity C Sp Capacity value of the blocking circuit capacity C T Capacity value of the tuning capacity C T1 Capacity value of the first part of the tuning capacity C T2 Capacity value of the second part of the tuning capacity D1 first DC connection D2 second DC connector E1 first electrode E2 second electrode H1 first RF connection H2 second RF connection K1 first contact element K2 second contact element L Batt Battery inductance value L M Inductance value of the matching inductance L Sp Inductance value of the resonant circuit inductance R metal Value of the ohmic resistance of the metallic parts of the battery REF Resonance frequency of the HF resonant circuit R electrolyte Value of the ohmic resistance across the electrolyte in the battery SPF blocking frequency SR1 series resonance frequency (block element 1) SR2 series resonance frequency (block element 2) Z M1 Impedance value of the first matching impedance Z M2 impedance value of the second matching impedance Z S Impedance value of the balancing impedance Z T1 Impedance value of the first partial tuning impedance Z T2 Impedance value of the second partial tuning impedance

Claims

NMR measuring head (2) for performing NMR measurements on a battery (1), comprising i) a measuring station (15) for a battery (1), with a first contact element (K1) for a first electrode (E1) of the battery (1) and a second contact element (K2) for a second electrode (E2) of the battery (1), ii) a tuning capacitor (30), and iii) a first RF connection (H1) and a second RF connection (H2) for an NMR console (6), wherein the first contact element (K1) and the second contact element (K2) are conductively connected for RF current via the tuning capacitor (30), so that an RF resonant circuit (3) can be set up with a battery (1) to be arranged at the measuring station (15), and wherein the first RF connection (H1) is conductively connected to the first contact element (K1) for RF current and the second RF connection (H2) is conductively connected to the second contact element (K2) for RF current,iv) a first DC terminal (D1) and a second DC terminal (D2) for a DC current element (4), and v) at least one first blocking element (B1) which is conductive for DC current and blocking for RF current at least in the region of a provided resonant frequency REF of the RF resonant circuit (3), wherein the first DC terminal (D1) is conductively connected to the first contacting element (K1) via the first blocking element (B1), and the second DC terminal (D2) is conductively connected to the second contacting element (K2) for DC current, wherein the at least one first blocking element (B1) ensures that the RF resonant circuit (3) is not affected by the DC current element (4). NMR measuring head (2) according to claim 1, characterized in that the measuring station (15) is set up for a battery (1) which is designed as a button cell (12). NMR measuring head (2) according to claim 1 or 2, characterized in that the second RF connection (H2) is connected to ground. NMR measuring head (2) according to one of claims 1 to 3, characterized in that the tuning capacitance (30) is formed with a first partial tuning capacitance (43) and a second partial tuning capacitance (44), wherein the first partial tuning capacitance (43) and the second partial tuning capacitance (44) are connected in series in the RF resonant circuit (3), and that a center tap (8) between the first partial tuning capacitance (43) and the second partial tuning capacitance (44) is connected to ground. NMR measuring head (2) according to one of claims 1 to 3, characterized in that the second contacting element (K2) is connected to ground. NMR measuring head (2) according to one of claims 1 to 4, characterized in that the NMR measuring head (2) further comprises a second block element (B2) which is permeable to DC current and blocking to RF current at least in the region of the intended resonant frequency REF of the RF resonant circuit (3), wherein the second DC connection (D2) is conductively connected to the second contacting element (K2) via the second block element (B2). NMR measuring head (2) according to one of the preceding claims, characterized in that the NMR measuring head (2) comprises one or more impedance matching elements (7). NMR measuring head (2) according to claim 7, characterized in that one of the RF connections (H1, H2), in particular the first RF connection (H1), is connected to its associated contacting element (K1, K2) via a matching capacitance (31). NMR measuring head (2) according to claim 7 or 8, characterized in that the tuning capacitance (30) and the impedance matching element(s) (7) are connected in such a way that at least approximately symmetrical potentials are obtained at the two contacting elements (K1, K2) during measurement operation, in particular wherein the first RF connection (H1) is connected to the first contacting element (K1) with a matching capacitance (31) in a conductive manner for RF current and the second contacting element (K2) is connected to ground with a balancing capacitance (38) in a conductive manner for RF current and the matching capacitance (31) and the balancing capacitance (38) have at least approximately the same capacitance value (CM, CS). NMR measuring head (2) according to one of the preceding claims, characterized in that at least one of the RF connections (H1, H2) is connected to its associated contacting element (K1, K2) via a DC blocking capacitance (8). NMR measuring head (2) according to one of claims 1 to 10, characterized in that a respective block element (B1, B2) is designed as a low-pass filter (9). NMR measuring head (2) according to claim 11, characterized in that the low-pass filter (9) is designed with a low-pass filter inductance (39). NMR measuring head (2) according to claim 12, characterized in that an inductance value LTPF of the low-pass filter inductance (39) is greater than an inductance value LBatt of the battery (1) in the RF resonant circuit (3), in particular wherein LTPF≥ 1 nH or 1 nH ≤ LTPF≤ 50 uH or 100 nH ≤ LTPF≤ 25 uH. NMR measuring head (2) according to one of claims 12 or 13, characterized in that a leakage capacitance (40) is connected between each block element (B1, B2) and its associated DC connection (D1, D2), which leads to ground, and that each series resonant frequency (SR1, SR2), which belongs to a series connection of the low-pass filter inductance (39) of the respective block element (B1, B2) with the associated leakage capacitance (40), is significantly smaller than the intended resonant frequency REF of the RF resonant circuit (3), in particular by at least a factor of 5 smaller, preferably by at least a factor of 10 smaller, most preferably by at least a factor of 50 smaller. NMR measuring head (2) according to one of claims 12 or 13, characterized in that a leakage capacitance (40) is connected between each block element (B1, B2) and its associated DC connection (D1, D2), which leads to ground, and that each series resonant frequency (SR1, SR2), which belongs to a series connection of the low-pass filter inductance (39) of the respective block element (B1, B2) with the associated leakage capacitance (40), corresponds at least approximately to the intended resonant frequency REF of the RF resonant circuit (3). NMR measuring head (2) according to one of claims 1 to 10, characterized in that a respective blocking element (B1, B2) is designed as a blocking circuit (11), wherein the blocking circuit (11) blocks in the region of the intended resonance frequency REF of the RF resonant circuit (3). NMR measuring head (2) according to one of the preceding claims, characterized in that a battery holder (10) is provided with which the battery (1) can be fixed to the measuring station (15), so that when the battery (1) is arranged in the battery holder (10), the first contacting element (K1) contacts the first electrode (E1) of the battery (1) and the second contacting element (K2) contacts the second electrode (E2) of the battery (1), in particular wherein the battery (1) can be elastically clamped in the battery holder (10) with the first contacting element (K1) and / or the second contacting element (K2), that the first contacting element (K1) and the second contacting element (K2) are galvanically isolated from each other, and that the first contacting element (K1) and the second contacting element (K2) are connected to each other by at least one capacitor (45, 46). NMR measuring head (2) according to claim 17, characterized in that the first contacting element (K1) and the second contacting element (K2) are connected to each other by two capacitors (45, 46), in particular on opposite sides of the battery holder (10). NMR spectrometer system (20), comprising: - an NMR measuring head (2) according to one of the preceding claims, - an NMR console (6) which is connected to the RF terminals (H1, H2), - a DC current element (4) which is connected to the DC terminals (D1, D2), - one or more control devices (26, 27) for the NMR console (6) and the DC current element (4), in particular comprising a control PC (27), - and a magnet (25) for generating a static magnetic field at the measuring station (15) for the battery (1), in particular wherein the magnet (25) comprises a shim system (24). NMR spectrometer system (20) according to claim 19, characterized in that the DC current element (4) is a DC charger (5) or a DC discharger. NMR measuring arrangement (28) comprising an NMR spectrometer system (20) according to claim 19 or 20 and a battery (1) arranged at the measuring station (15) for the battery (1), wherein a first electrode (E1) of the battery (1) is contacted with the first contacting element (K1), and a second electrode (E2) of the battery (1) is contacted with the second contacting element (K2). Use of an NMR measuring arrangement (28) according to claim 21, wherein the battery (1) is charged or discharged simultaneously with the DC current element (4), and an NMR measurement is performed on the battery (1) with the NMR console (6) and the NMR measuring head (2).

Images