Battery electrolyte characterization using ultralow-field nmr

Abstract

A method includes thermally polarizing nuclear spins in a battery cell in a polarization region. The battery cell includes an electrolyte disposed in a housing. The method includes positioning the battery cell in a detection region. The method includes receiving, by one or more atomic magnetometer sensors, NMR signals from the electrolyte. The method includes characterizing, using the NMR signals, one or more properties of the electrolyte disposed in the battery cell. The one or more properties of the electrolyte include at least one of electrolyte composition, electrolyte loss, electrolyte degradation, or electrolyte amount.

Description

Atty. Dkt. No.046434-0887 BATTERY ELECTROLYTE CHARACTERIZATION USING ULTRALOW-FIELD NMR CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This application claims the benefit and priority of U.S. Provisional Patent Application No. 63 / 649,837, filed on May 20, 2024, the entirety of which is incorporated by reference herein. STATEMENT OF GOVERNMENT INTEREST

[0002] This invention was made with government support under CHE2108205 awarded by the National Science Foundation. The government has certain rights in the invention. TECHNICAL FIELD

[0003] The present disclosure generally relates to the field of nuclear magnetic resonance. BACKGROUND

[0004] Batteries can be used for electric vehicles, portable electronics, alternative energy harvesting, and energy storage. SUMMARY

[0005] Lithium-ion batteries represent a transformative technology for electric vehicles, portable electronics, and alternative and / or renewable energy. Many battery failures can result from the loss or chemical degradation of electrolyte. However, nondestructive battery- diagnostic techniques can be limited, and obtaining critical battery parameters from functioning devices can be difficult. Other efforts can include inside-out magnetic resonance imaging (MRI) and magnetometry, but the nature of the electrolyte may not be characterized in detail (only through indirect diagnoses via, for example, changes in magnetic susceptibility). Presented herein is an experimental setup for identification of electrolyte amount, composition, and degradation through battery enclosures, using techniques related to zero-to-ultralow-field nuclear magnetic resonance (ZULF NMR) with optical atomic magnetometers as detection elements. In this modality, frequencies of electromagnetic fields can be low enough to enable penetration of battery housing, metal casings, and electrode materials, which is not typically possible with high-field NMR due to skin-depth limitations. The low background magnetic field and related resonance frequencies can allow for the penetration of thick stacks of battery 1 4920-8416-5164Atty. Dkt. No.046434-0887 housing and electrodes. Both the solvent and Li-salt components of the chemical signature can be quantified. The apparatus can be compatible with measurement of pouch-cell batteries.

[0006] At least one aspect of the present disclosure is directed to a method. The method can include thermally polarizing nuclear spins in a battery cell in a polarization region. The battery cell can include an electrolyte disposed in a housing. The method can include positioning the battery cell in a detection region. The method can include receiving, by one or more atomic magnetometer sensors, NMR signals from the electrolyte. The method can include characterizing, using the NMR signals, one or more properties of the electrolyte disposed in the battery cell. The one or more properties of the electrolyte include at least one of electrolyte composition, electrolyte loss, electrolyte degradation, or electrolyte amount.

[0007] Another aspect of the present disclosure is directed to a system. The system can include a magnetic shield. The magnetic shield can include a detection region. The system can include a battery cell. The battery cell can include an electrolyte disposed in a housing. The battery cell can be disposed in a holder. The holder can be disposed in the detection region. The system can include a magnet configured to thermally polarize nuclear spins in the battery cell in a polarization region. The system can include one or more atomic magnetometer sensors configured to receive NMR signals from the electrolyte. The system can include a processor configured to characterize, using the NMR signals, one or more properties of the electrolyte disposed in the battery cell. The one or more properties of the electrolyte can include at least one of electrolyte composition, electrolyte loss, electrolyte degradation, or electrolyte amount.

[0008] The summary is illustrative only and is not intended to be in any way limiting. Other aspects, inventive features, and advantages of the devices and / or processes described herein, as defined solely by the claims, will become apparent in the detailed description set forth herein and taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE FIGURES

[0009] The details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

[0010] Figure 1A illustrates an experimental apparatus, according to an embodiment.

[0011] Figure 1B illustrates electrolyte chemical compositions, according to an embodiment. 2 4920-8416-5164Atty. Dkt. No.046434-0887

[0012] Figure 1C illustrates a measurement sequence, according to an embodiment.

[0013] Figure 2A illustrates an energy-level diagram, according to an embodiment.

[0014] Figure 2B illustrates a plot of characteristic measured and simulated low-field NMR signals, according to an embodiment.

[0015] Figure 3A illustrates stacked plots showing the measured electrolyte signal at a 2.69 µT background field, according to an embodiment.

[0016] Figure 3B illustrates plots of solute and solvent signals for each sample, according to an embodiment.

[0017] Figure 3C illustrates a plot of calculated ^^^^^ିconcentration for each sample, according to an embodiment.

[0018] Figures 4A and 4B illustrate results from ethylene-carbonate / dimethyl carbonate and LiPF6 quantification over time based on Figures 3A and 3B, according to an embodiment.

[0019] Figure 5 illustrates results from functional pouch-cell batteries, according to an embodiment.

[0020] Figure 6 illustrates a method for nondestructive observation of an electrolyte in a battery, according to an embodiment.

[0021] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and made part of this disclosure. DETAILED DESCRIPTION

[0022] Following below are more detailed descriptions of various concepts related to, and implementations of, methods, apparatuses, and systems for battery electrolyte characterization. The various concepts introduced above and discussed in greater detail below may be implemented in any of a number of ways, as the described concepts are not limited to any 3 4920-8416-5164Atty. Dkt. No.046434-0887 particular manner of implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes.

[0023] The systems and methods of the present disclosure are directed to ultralow-field NMR (e.g., microtesla NMR) for direct nondestructive observation of electrolyte composition and degradation through battery housing. To directly and nondestructively observe electrolyte signatures inside batteries, a ZULF setup that includes magnetic shielding, atomic magnetometers in a “gradiometric quadrature” detection scheme, and a sample shuttle from a 1 T polarization field into a low detection field (e.g., pT, nT, μT) can be used to measure a composition of LiPF6in ethylene carbonate with dimethyl carbonate (e.g., EC / DMC) inside coin-cell batteries. Although metallic battery components can generate challenges with respect to shuttling-induced eddy currents and associated magnetic noise, operating the apparatus with a detection field in the microtesla range can allow for sensitive quantification of electrolyte content. Electrolyte spectra can be recorded through a battery housing. Both the solvent and the Li-salt components of the chemical signature can be quantified. Electrolyte degradation products can be detected using this approach. The electrolyte concentrations, resonance frequencies, and linewidths may be used as diagnostic tools for battery life and battery health.

[0024] Reliable and rechargeable batteries can support technological advances, such as the electrification of transportation or the use of alternative energy sources. Distinguishing a good battery from a bad battery and determining the reason for a failing battery can be ascertained by various battery-diagnostic techniques. The systems and methods of the present disclosure can include application of a spectroscopic method for nondestructive sensing of the state of a battery electrolyte. Because the electrolyte forms a component of a rechargeable battery cell, and electrolyte loss or degradation is a common battery failure mode, the presented techniques can provide important device data.

[0025] Rechargeable batteries, especially lithium-ion batteries, can allow for electrification of transportation and the use of alternative energy sources. One pain point in current technology can include the limited ability of analytical or diagnostic techniques to detect changes or defects within realistic battery cells (compared to purely research cells) in a nondestructive fashion. Magnetic resonance imaging can be adapted to sense changes in the structure or magnetic susceptibility of battery materials, and thereby provide a link between external measurements and internal processes. This type of indirect approach can be demonstrated with magnetometry, where atomic magnetometers can be used to detect changes in the induced field as a function of applied background magnetic fields—specifically showing, for example, nonuniform 4 4920-8416-5164Atty. Dkt. No.046434-0887 lithium incorporation into the cathode. Further extensions of MRI and magnetometry-based approaches to battery diagnostics can include the detection of small (e.g., µA) currents either during charging / discharging or during resting periods, as well as the use of alternative detection media and other types of sensors / modalities, such as magnetically induced tomography detected by nitrogen-vacancy (NV) centers in diamond allowed access to further observables for battery assessment. All these techniques can provide the ability to probe either changes in solid components as a function of Li incorporation, or changes in electrical current distributions through the measurement of magnetic fields around the batteries.

[0026] The electrolyte itself has so far not received much attention in the aforementioned approaches to nondestructive testing, nor was it generally possible to detect changes in electrolyte composition directly. The nature, distribution, and composition of the electrolyte can be important to the proper functioning of a cell. Changes such as leakage or electrolyte degradation due to aging processes are frequently the reason for battery failures.

[0027] Typical battery electrolytes can include a solvent (e.g., a mixture of ethylene carbonate (EC) with dimethyl carbonate (DMC)) and the solute (e.g., a Li salt such as LiPF6), but the technique is not limited to the chemical specifics of the composition. The systems and methods of the present disclosure include the study of battery-cell enclosures containing these chemicals to demonstrate the ability to obtain characteristic spectroscopic signatures that allow quantification of the total electrolyte amount as well as its composition, including the LiPF6content. The measurement of electrolytes through aluminum (Al) enclosures can be of particular interest, as Al is the typical housing for the commercial flat Li-ion pouch and prismatic cells widely used in electric vehicles, portable electronics, and renewable-energy storage.

[0028] One option for obtaining spectroscopic electrolyte signatures from the inside of a cell is to examine it with nuclear magnetic resonance (NMR). At the frequencies commonly employed in NMR spectroscopy (e.g., hundreds of MHz), however, the skin depth of electromagnetic radiation in metal is only on the order 10 μm, which prevents fields from penetrating the cell during nuclear-spin excitation and detection. Quantification and reproducibility are challenging due to field-shaping effects and tuning variabilities. Because skin depth scales inversely with the square root of frequency, even low-field benchtop instruments (e.g., based on permanent magnets, with proton precession frequencies on the order 10 MHz) still only enable penetration of tens of μm of metal at best. For this reason, and due to sample-size limitations, battery testing with benchtop NMR is typically limited to studies of 5 4920-8416-5164Atty. Dkt. No.046434-0887 research pouch cells which fit into an NMR tube, or to inline studies of redox flow cells. By contrast, in zero-to-ultralow-field (ZULF) NMR experiments, the resonance frequencies of nuclear-spin samples can span the range from Hz to kHz and are tunable through the application of a background field. Spin excitation can be performed using pulses of static magnetic fields, and metals are therefore essentially transparent to the applied and measured electromagnetic waves.

[0029] In NMR spectroscopy, internal couplings and especially J-couplings—indirect spin-spin couplings mediated by the electrons shared in chemical bonds—can be much smaller than the Zeeman interaction. In the ZULF-NMR regime, the situation is opposite: the Zeeman interaction is much weaker than the J-coupling interaction, such that Zeeman coupling represents a perturbation to the J-coupling Hamiltonian. Thus, the molecular information is encoded in so-called J-spectra, rather than in chemical-shift values. These spectra, which arise from angular-momentum selection rules, can be used to obtain molecular fingerprints of studied samples. ZULF-NMR spectra do not suffer from susceptibility-induced line broadening even in materials with complex internal structure, and consequently display narrower spectral lines compared to higher-field measurements.

[0030] At the relatively low frequencies of signals in ZULF-NMR spectroscopy, inductive detection is largely ineffective due to decreased sensitivity, so detection is typically performed with either superconducting quantum-interference devices (SQUIDs) or (noncryogenic) atomic magnetometers, also called optically pumped magnetometers (OPMs). Both SQUIDs and the most sensitive atomic magnetometers require operation in a near-zero-field environment, where Earth’s magnetic field is screened by means of magnetic shielding. Furthermore, to boost signals, nonequilibrium spin polarization of samples is created either by prepolarizing them in a stronger magnetic field (using a permanent magnet or electromagnet) or by employing hyperpolarization techniques. With these implementations, ZULF NMR can be applied to studies of fundamental physics, chemical fingerprinting of biological samples and metabolism using J-spectroscopy, as well as relaxometry at hypogeomagnetic fields. Battery diagnostics represent a new direction in the application of ZULF-NMR instrumentation.

[0031] To demonstrate the sensitivity of the method to the smallest possible realistic volume of battery electrolyte, experiments were performed on ∼1 mm-thick Al coin-cell enclosures with a sealed form factor and containing less than 100 μL of electrolyte. Examination of the measured spectra allowed the detection and assignment of electrolyte 6 4920-8416-5164Atty. Dkt. No.046434-0887 signals such that molar concentrations, as well as changes in composition and potentially degradation, could be quantified.

[0032] A ZULF-NMR setup based on thermal prepolarization, mechanical shuttling between the prepolarization and measurement regions, and room-temperature, quadrature detection using atomic magnetometers can be employed. Figure 1A shows the apparatus as used in the experiments presented here. Figure 1A illustrates an experimental apparatus (e.g., system 100). The apparatus can be operated at a constant background field of 2.69 µT along െ^̂^ inside the guiding solenoid, corresponding to an applied current of 600 µA and a proton precession frequency of 114.6 Hz. For this implementation and illustration, it can be optimal, but other background field ranges are possible. Prior to measurement, each sample cell can be enclosed in a 3D-printed PLA holder affixed to the plastic gear rack and positioned inside the 1 T permanent magnet (e.g., Halbach array). The apparatus can be mobile and produced cheaply. The apparatus can include on-board monitoring of devices. The apparatus can include an ultralow-field NMR apparatus. The system 100 can be used for mechanically shuttling thermally nuclear-spin-polarized samples to a hypogeomagnetic measurement region, where spin manipulation and subsequent measurement take place.

[0033] Figure 1A illustrates an experimental ultralow-field NMR apparatus for mechanically shuttling thermally nuclear-spin-polarized samples to a hypogeomagnetic measurement region, where spin manipulation and subsequent measurement take place. The shuttling distance from the prepolarizing magnet to the measurement region is 36 cm. The cut- out shows the plastic holder containing a sample cell inside the piercing solenoid, where a tunable measurement field is used to produce magnetic resonances detected by atomic magnetometers (sensitive axes indicated by the four arrows).

[0034] The system 100 can include a magnetic shield 105 (e.g., µ-metal shield). The magnetic shield 105 can include one or more layers of magnetic shielding. The magnetic shield 105 can include a detection region 107. For example, the detection region can be disposed within the magnetic shield 105. The system 100 can include a plurality of Helmholtz coils 108 disposed in the detection region. The plurality of Helmholz coils 108 can be disposed around the detection region. The system 100 can include a solenoid 110 (e.g., piercing solenoid) disposed in the magnetic shield 105.

[0035] The system 100 can include a battery cell 115. The battery cell 115 can include an electrolyte (e.g., electrolyte disposed in a housing of the battery cell). The electrolyte can 7 4920-8416-5164Atty. Dkt. No.046434-0887 include one or more solvents. The electrolyte can include at least one of ethylene carbonate, dimethyl carbonate. In some examples, the electrolyte can include propylene carbonate. The electrolyte can include one or more solutes (e.g., analytes). The electrolyte can include LiPF6. The electrolyte can be disposed in a housing. The housing can include a metal. The metal can include aluminum (Al). The battery cell 115 can be disposed in a holder 120 (e.g., plastic holder, 3D printed holder). The holder 120 can be disposed in the detection region. The battery cell 115 can be disposed in the solenoid. The holder 120 can enclose the sample (e.g., sample cell, sample battery cell) inside the solenoid 110. The holder 120 can be disposed in the plurality of Helmholz coils 108.

[0036] The battery cell 115 can include a coin cell. The coin cell case (e.g., housing) can be constructed out of ultra-pure aluminum metal (e.g., 99.9%) to reduce magnetic impurities. Lithium hexafluorophosphate (LiPF6 (s)) salt can be dissolved into a 50v:50v mixture of ethylene carbonate (EC: (CH2O)2CO(s)) and dimethyl carbonate (DMC: OC(OCH3)2(l)), to form 0.5, 1 (LP30), 1.5, 2, and 2.5 M salt concentration electrolytes. A total of up to 150 µL of the various-concentration electrolytes can be pipetted into each of the coin-cell cases. The coin cells can be sealed using a plastic insert, to prevent magnetic impurities from the coin-cell crimper. All samples can be stored, handled, and processed in an argon atmosphere (<1 ppm O2 and H2O). Other types of cells could be studied as well, such as pouch cells, cylindrical, or prismatic cells.The system 100 can include a magnet 125 (e.g., 1T prepolarization magnet). The magnet 125 can be configured to thermally polarize nuclear spins in the battery cell 115. For example, the magnet 125 can thermally polarize the battery cell 115 in a polarization region. The shuttling distance from a magnet 125 (e.g., prepolarizing magnet) to the measurement region can be in the range of 30 cm to 40 cm. In one example, the shuttling distance is 36 cm. The battery cell 115 can be shuttled from the magnet 125 to the detection region 107. For example, the battery cell 115 can be shuttled from the magnet 125 to the detection region 107 by a gear rack and shuttling tube (e.g., plexiglass shuttling tube).

[0037] The system 100 can include one or more sensors 130. The sensor 130 can include a magnetometer. The magnetometer can include an atomic magnetometer or atomic magnetometer sensor. The sensor can include a superconducting quantum-interference device. The sensor can include a optically pumped magnetometer. The one or more atomic magnetometer sensors can be configured to receive NMR signals from the electrolyte. The NMR signals can be in a range of less than 500 Hz. The sensors can include optical sensors (e.g., ultrasensitive optical sensors) that can detect magnetic fields. A tunable measurement 8 4920-8416-5164Atty. Dkt. No.046434-0887 field can be used to produce magnetic resonances, which are detected by the magnetometer. The magnetometer can include an Rb vapor cell. The sensitive axes are indicated by arrows from the Rb vapor cells. The magnetometer can be disposed in a volume bounded by the plurality of Helmholz coils 108. The magnetometer can be disposed in a volume bounded by a ferrite enclosure 135.

[0038] The system 100 can include a processor configured to characterize, using the NMR signals, one or more properties of the electrolyte disposed in the battery cell. The one or more properties of the electrolyte can include at least one of electrolyte composition, electrolyte loss, electrolyte degradation, or electrolyte amount. Properties of the electrolyte (e.g., electrolyte composition, degradation of the electrolyte) can be measured through the metal housing of the battery cell by using ultra-low field NMR spectroscopy. The information gathered through these measurements can provide a way of characterizing battery cells to diagnose defects, predict their lifetimes, and allow for the classification of battery cells. Such measurements can be taken at various stages in a battery’s life cycle, and can be used to source high quality battery cells, examine them during and after testing, and classify them according to quality. The measurements can be performed in functioning battery cells. The electrolyte of the battery cell can be studied as a function of charge state. Different types of battery cell geometries and different electrolyte compositions can be studied and measured. The processor can be configured to generate a spectrum for a regime in which ω0<< J, wherein ω0is a Larmor frequency of a spin system and J is a coupling constant characterizing a strength of spin-spin interaction. The processor can detect any substance through a metal container. The processor can diagnose one or more defects of the battery cell using the NMR signals. The processor can characterize the one or more properties of the electrolyte during operation of the battery cell. The processor can pre-polarize nuclear spins in a location of the battery cell. The processor can acquire electrolyte signals from the electrolyte at the location of the battery cell.

[0039] Figure 1B illustrates electrolyte chemical compositions. The electrolyte can include one or more analytes (e.g., solutes). The analyte can include lithium hexafluorophosphate (LiPF6). The electrolyte can include one or more solvents. The solvent can include ethylene carbonate (EC). The solvent can include dimethyl carbonate (DMC). The electrolyte can be disposed in the battery cell 115. For example, 100 µL of electrolyte can be disposed in a 1 mm- thick Al coin cell. In one example, the electrolyte can be composed of different amounts of LiPF6dissolved in a 50:50 vol% mixture of EC / DMC. 9 4920-8416-5164Atty. Dkt. No.046434-0887

[0040] The electrolytes selected for this study were composed of different amounts of LiPF6 dissolved in a 50v:50v mixture of EC / DMC (Figure 1B). In ZULF-NMR spectra, one can therefore expect to observe a lower-frequency family of signals—depending on the background field and associated Larmor frequencies—which arise from Liା, PF^ି, and the EC / DMC solvent protons (henceforth referred to as the near-zerofrequency peaks, “nZF- peaks”). Specifically, this study deals with7Li, coupled31P and19F spins, and1H. In the case of the PF^ିsystem, the Zeeman interaction with the measurement field (produced by the piercing solenoid, Figure 1A) lifts the degeneracy inside manifolds of total spin angular momentum F, leading to transitions between states inside the same manifold observed as nZF peaks. In addition, the PF^ିunit gives rise to transitions at higher frequencies of where ^^ ൌ 711 Hz is the J-coupl 31 19^ி ing constant between P and Fnuclei (20) (signals referred to as the “J-peaks” in the following). See Figure 2A for energy- level diagrams.

[0041] For the implementation of the method, the focus is on the nZF-manifold for two reasons: (1) the J-peaks are approximately 200 times weaker than the nZF-peaks for PF^ି, which would complicate the measurement of smaller sample volumes within a reasonable amount of time; (2) the higher frequencies of the J-peaks fall outside the sensitive bandwidth of the magnetometers used in this study—signals are detectable up to 500 Hz, with flat sensor response in a 100 Hz band.

[0042] Figure 1C illustrates a measurement sequence. A single measurement cycle (e.g., scan, sequence) can include (1) 10 s nuclear-spin polarization in the magnet, (2) 100 ms shuttling 36 cm into the detection region at the center of the magnetic shield (Twinleaf MS1- LF), (3) 200 µs application of a 30 µT π / 2 magnetic-field pulse along െ^^^ to rotate magnetization into the x-y detection plane, (4) at least 5 s four-channel acquisition of the free- induction-decay (FID) signal by two dual-axis QuSpin Zero-Field Magnetometers (QZFM Gen-2) during magnetization precession in the background field, and (5) return of the sample to the starting position inside the magnet. The sensor can be pointing into the x-direction, and the other along the y-direction to enable quadrature detection.

[0043] Figure 1C illustrates the measurement sequence for a single signal readout (or “scan”) including prepolarization, shuttling, application of a 90° magnetic-field pulse to rotate magnetization into the detection plane, and detection of a decaying magnetic-dipole signal as the magnetization precesses freely in the applied solenoid field. Finally, the sample is shuttled 10 4920-8416-5164Atty. Dkt. No.046434-0887 back to the prepolarizing magnet for the next scan. Experiments typically included many scans which were averaged to improve the measured signal-to-noise ratio (SNR) of electrolyte signals from sample cells containing less than 100μL of electrolyte.

[0044] The measurement sequence for a single signal readout (e.g., scan) can include prepolarization, shuttling, application of a 90° magnetic-field pulse to rotate magnetization into the detection plane, and detection of a decaying magnetic-dipole signal as the magnetization precesses freely in the applied solenoid field. Finally, the sample can be shuttled back to the prepolarizing magnet for the next scan. Experiments can include many scans which were averaged to improve the measured signal-to-noise ratio (SNR) of electrolyte signals from sample cells containing less than 100 μL of electrolyte.

[0045] The subfield of ZULF NMR can be used to study the regime where internal spin couplings in the measured sample—including indirect spin-spin couplings mediated by chemical bonds, known as J-couplings—dominate coupling to the external magnetic field and associated Zeeman shifts. Specifically, in this regime, ω0≪ J, where ω0is the Larmor frequency of the spin system and J is the coupling constant characterizing the strength of spin- spin interaction. In contrast to NMR spectroscopy where atomic information is encoded in chemical-shift values, J-coupling eclipses Zeeman interactions, leading to so-called J-spectra. Achieving such a condition can require measurement in a hypogeomagnetic field environment, where Earth’s magnetic field is screened by means of magnetic shielding. The ZULF regime (e.g., ω0 ≪ J) is not universal, and it depends on which sample is analyzed. For the example of two coupled nuclear spins of31P and19F, they are in the ZULF regime when the difference in Larmor frequency of both spins is smaller than their J-coupling. Considering a J-coupling of 711 Hz, the ZULF regime includes fields below approximately 4.82 µT, considering the difference in Larmor frequencies 4.82 µT×2π×(40.078 -16.546) Hz / µT = 712 Hz. The measurements can be performed at Larmor frequencies of about 200 Hz, 100 Hz, or below, which is much less than the J-coupling constant of about 700 Hz. For other compounds, the couplings may be smaller and use Larmor frequences to retain the ZULF regime. Because sensitivity limitations can preclude the use of inductive coils for detecting the low-frequency NMR signals, detection can be performed with either superconducting quantum-interference devices or noncryogenic atomic magnetometers, also called optically pumped magnetometers. Furthermore, prior to nuclear-spin evolution and detection, nonequilibrium spin polarization may be prepared by either a permanent magnet (e.g., thermal polarization) or hyperpolarization techniques. In addition to fundamental studies, ZULF NMR methodology can be applied to 11 4920-8416-5164Atty. Dkt. No.046434-0887 chemical fingerprinting of biological samples using J-spectroscopy, as well as relaxometry at hypogeomagnetic fields. Battery diagnostics can use ZULF instrumentation and give access not only to the electrolyte J-spectra, but also to Larmor precession of electrolyte magnetization at low fields.

[0046] A ZULF setup can be chosen based on thermal polarization, mechanical shuttling between the polarization and measurement regions, and room-temperature, quadrature detection using atomic magnetometers. The two spectral components that can be identified as characteristic to the electrolyte solutions can correspond to the ^^^^^ିunit and the1H nuclei of the solute and solvent, respectively. The former can give rise to transitions at frequencies around 3 / 21JPF, 5 / 21JPF and 7 / 21JPF, where1JPF ≈ 700 Hz is the J-coupling constant between31P and19F nuclei. At the same time, both systems can experience a small Zeeman interaction with the external field produced by the solenoid as shown in Figure 1, leading to additional resonances transitions centered at the very low Larmor frequencies of19F and1H, respectively. The bandwidth of the sensors can enable the detection of signals in the frequency range between DC and 500 Hz, whereas the J-peaks can appear at resonance frequencies above 1 kHz, outside the spectral window. Thus, the focus can be on precession measurements of both the solute and solvent at frequencies that can be easily manipulated in order to reduce spectral overlap, baseline distortions, and noisy spectral regions. The complexity of the ^^^^^ିspectrum can readily be reproduced by simulations as shown in Figure 2B and can stem from lifting the degeneracy inside spin manifolds due to the Zeeman perturbation of ZULF eigenstates.

[0047] To demonstrate the sensitivity of the method to the smallest possible realistic volume of battery electrolyte, experiments can be performed on Al battery enclosures in a coin- cell geometry, containing up to 150 µL of electrolyte. Examination of the relatively strong^^^^ ൌ 0 peak manifold (where ^^ is the total angular momentum of the nuclear-spin system)can allow for the detection of electrolyte signals to the level that total amounts and LiPF6 concentration, as well as changes in concentrations and degradation, can be detected. Other types of electrolytes could be analyzed in a similar manner with different resonance frequencies.

[0048] Ultra-sensitive vector magnetometers, such as sold under the tradename QuSpin magnetometers, can be employed in an SNR-enhancing “gradiometric quadrature” detection scheme to measure a composition of LiPF6in EC / DMC through battery housing. The samples can be thermally polarized at 1 T and shuttled to the magnetically shielded detection region. Although metallic battery components can generate challenges with respect to shuttling- 12 4920-8416-5164Atty. Dkt. No.046434-0887 induced eddy currents and associated magnetic noise, operating the apparatus at a minimum background magnetic field in the microtesla range can allow for sensitive measurement of electrolyte signals. Production of gradiometric quadrature frequency spectra from the raw magnetometer time traces can be carried out using Matlab. Further post-processing and spectral-lineshape correction can be implemented in Mathematica.

[0049] Figure 2B shows a characteristic electrolyte spectrum measured from a sample cell of coin-cell geometry, at a background (measurement) field of 2.7 μT. Although nZF-peaks could in principle be measured at arbitrarily low background fields, practical considerations motivated a choice of field in the microtesla range, corresponding to a1H Larmor frequency of approximately 115 Hz; all PF^ିand EC / DMC signals appear within the spectral range 86–130 Hz. This approach allowed for the movement of the signals of interest out of a lower-frequency region where significant noise was observed due to shuttling of the conductive aluminum housing. The complexity of the PF^ିnZF-manifold is reproduced by simulations using the Spinach package in Matlab and stems from lifting the degeneracy inside spin manifolds due to the Zeeman perturbation of ZULF eigenstates as illustrated in Figure 2A. A simulation of the EC / DMC proton signal is also included, as well the measured water-proton signal from a calibration cell filled with deionized water. Finally, the background signal from an empty cell is displayed to identify artifacts not arising from the spin sample, such as the noise peak at 84 Hz. The sample volume was only about 80 μL, and it is thus quite promising that electrolyte NMR signals can be obtained from such a small volume using atomic magnetometers. For completeness, the Li+ signal could be identified at lower frequency, here around 45 Hz. For subsequent analysis, however, the signals of PF^ିand EC / DMC were used, since they had larger SNR and were farther away from spectral noise features.

[0050] In order to consistently extract electrolyte concentrations from all recorded experimental spectra, solute and solvent signals were integrated over the regions between the dotted lines indicated in Figure 2B—including the two largest PF^ିpeaks in the spectral window 93.38–101.32 Hz, and the solvent proton peak in the spectral window 110.65–118.59 Hz. Although the latter integration region also contains a smaller PF^ିsignal around 116 Hz, this contribution is negligible compared to the much larger (by two orders of magnitude) proton signal.

[0051] Figure 2A illustrates an energy-level diagram showing manifolds containing eigenstates of the J-coupling Hamiltonian for the PF^ିspin system. Application of a background magnetic field ^^௭in the solenoid (Figure 1A) lifts the degeneracy of the eigenstates within each 13 4920-8416-5164Atty. Dkt. No.046434-0887 manifold, splitting the energy levels as indicated schematically. Each ^^^, where m is an integer, refers to the transition frequency between energy levels of the same manifold. Here,^^ ൌ 711 Hz and the Zeeman splitting is approximately linear in the ultralow field regime; ^^^and ^^^are the gyromagnetic ratios of phosphorus and fluorine, respectively.

[0052] Figure 2B illustrates characteristic measured and simulated NMR signals at a 2.7μT background magnetic field. The graph displays the recorded electrolyte signature from a sample cell, a background noise measurement of an empty cell, simulation of the PF^ିspin system, simulation of the solvent proton signal, and a recorded spectrum from an identical cell containing deionized water for calibration. The near-zero-frequency (nZF) peaks corresponding to the ^^^transitions are labeled beneath the simulated spectrum. Experimental spectra are obtained from averages of 10000 scans. The shaded areas indicate the frequency ranges used for calculation of concentrations,. Electrolyte experimental data was phased using the relative zeroth-order phases −30º, 150º, 0º, and −90º in four different spectral regions, respectively. Double dashes delimitate these phased regions. The spectra are offset for visual clarity, and vertical orange dashed lines provide an aid to the eye for the measured PF^ିpeaks with lower SNR. The SNR of the PF^ିpeaks are 13, 74, 37, 20, and 5 for the peaks at approximately 87, 96, 99, 115, 120, and 128 Hz, respectively—calculated as the maximum signal amplitude divided by the standard deviation of a neighboring noise region from 132 to 140 Hz. The linewidths (full width at half maximum, FWHM) of these peaks range from 1 to 1.5 Hz.

[0053] In a pure water sample polarized at ^^^ ൌ 1 ^^ and room temperature (20°C), theexpected thermal polarization of proton spins is:where ^^^ಹ / 2^^ ൌ 42.6 ^^^^^^ / ^^ and ^^ ൌ 1 / 2. This expression yields^42.6 ൈ 10^^^^^ ∙ ^^ି^^^6.63 ൈ 10ିଷସ^^ ∙ ^^^^1^^^^^ ൌ 21.38 ൈ 10 ^^ ∙ ^^ ^293^^^ ൌ 3.5 ି^௧^^^^ ^ ିଶଷ ି^^ ൈ 10

[0054] Given the molar concentration of water protons, ^^ ൌ 110 ^^, the amplitude ofsample magnetization (e.g., magnetic moment per unit volume) can then be estimated as 14 4920-8416-5164Atty. Dkt. No.046434-0887 ^^ ൌ ^^ ∙ ^^1ுℏ^^ ∙ ^^௧^^^^Eq.2 ൌ^110 ^^^^^^ ∙ ^^ି^^^6.02 ൈ 10ଶଷ^^^^^^ି^^^42.6 ൈ 10^^^^^ ∙ ^^ି^^3.3 ൈ 10ି^^ ଶ ି^^ ∙ ^^ ∙ ^^ൌ 3.3 ൈ 10ି^^^ ∙ ^^ି^

[0055] For a sample of volume ^^ ൌ 150 µ^^, the magnetic moment is then ^^ ൌ ^^ ^^^ ൌ 5.0 ൈ 10ି^^ ^^ ^ ^^ଶ. In the ideal case of a uniformly magnetized sphere, giving rise toa pure dipole magnetic field outside, and ignoring any relaxation mechanisms affecting ^^, the maximum gradiometric quadrature amplitude measured at the sensor standoff distance 17.5 ^^^^ from the center of the sample is 3^^ ^^3^1.26 ൈ 10ି^^^ ∙ ^^ିଶ^^5.0 ൈ 10ି^^^^ ∙ ^^ଶ^Eq.3 ^^ ൌ ^ൌ 2^^^^ଷ2^^^0.0175^^^ଷ^ 100^^^^.

[0056] Here the vacuum magnetic permeability, µ0, can be used and the magnetic-field amplitude can be reported to one significant figure. In one embodiment (e.g., a realistic case), the correction factor for non-spherical geometry (disc) may not be critical as signals can be compared arising from the same sample geometry. There can be an analogous calculation for electrolyte spin systems, starting from measured signal field.

[0057] Figure 3A presents the spectra for a series of samples prepared with different electrolyte concentrations and approximately the same total liquid content. The bottom trace in Figure 3A was acquired using a reference vial of known electrolyte concentration. In Figure 3B, the solute and solvent signals are compared for each sample based on the integrals extracted from the indicated shaded spectral regions. The ratio of integrated solute and solvent signals was compared to the signals from the calibration-vial data (Figure. 3A) in order to obtain normalized concentration values. Figure 3C shows the calculated PF^ିconcentration for all cells, normalized to the 2M calibration sample, following the relation: ^^^^షల ൌ ^^^

[0058] Here, ^^ is the measured signal (integrated area of the peak, Figure 3B). This calibration approach was chosen in part because the total liquid amount in each cell varied due to the production method (in the process of sealing the cells, some spillage was inevitable). Therefore, comparing signal ratios between the samples and reference vial data allowed us to 15 4920-8416-5164Atty. Dkt. No.046434-0887 remove uncertainty arising from different liquid amounts or potential leakage. The signal from the vial is much larger than that from the sample cells (Figure 3A), due to both an increased sample volume (the vial contained 1.5mL of electrolyte while the cells typically contained ∼ 80 μL) and a more efficient geometry (the sensor arrangement depicted in Figure 1A is more suitable for the approximately cylindrical geometry of the vial, rather than the disc-like coin cells). These factors, as well as possible reduction of magnetization due to fields induced by shuttling conductive material, do not affect the relative quantification method of Eq. 4. For samples 3 and 4, the SNR of electrolyte signals, barely visible in Figure 3A, are relatively low, and hence the calculated concentrations have larger error bars in Figure 3C.

[0059] To demonstrate the robustness of the setup and the reproducibility of measurements, partitions of data from the same (largest-SNR) sample at different time intervals under identical experimental conditions were analyzed, as displayed in Figures 4A and 4B. The standard errors of solute and solvent signals extracted from this data set were used to calculate the error bars displayed in Figures 3B and 3C. In this analysis, uncertainty on measured signals (peak integrals) is assumed to scale inversely with SNR, such that higher SNR corresponds to a smaller error bar (see SI for further details). These error bars account for both statistical uncertainty as well as possible systematic uncertainty over the course of the measurement cycle.

[0060] Figure 3A illustrates stacked plots showing the measured electrolyte signals at a 2.7 μT background field from a series of sample cells filled with electrolyte of different nominal (prepared) LiPF6concentrations. The spectra were obtained from averages of 10,000 scans, apart from sample 1 and the calibration vial for which 8913 and 256 scans were collected, respectively. The large number of scans was selected to improve SNR of measured signals from the cells, as well as to suppress the powerline harmonic at 100 Hz.

[0061] Figure 3B illustrates plots of solute and solvent signals for each sample shown in Figure 3A. Quantification of signals obtained from integration of the shaded areas indicated in Figure 3A for the solute and solvent peaks (top and bottom plots, respectively). Error bars correspond to the standard errors obtained in Figures 4A and 4B and their values as a fraction of the signal scale inversely with SNR.

[0062] Figure 3C illustrates a plot of calculated ^^^^^ିconcentration for each sample. LiPF6 concentrations obtained from the measurements in Figure 3B and propagation of errors are shown. As is evident from Figure 3C, comparing the measured LiPF6concentrations to the 16 4920-8416-5164Atty. Dkt. No.046434-0887 nominal (prepared) concentrations, for the majority of samples, the measured concentrations agree with the nominal values to within 10%. Furthermore, the relative stability or loss / leakage of electrolyte signals could be tracked through time-separated measurement of the same cells. Samples 6 and 7 display larger deviations between nominal and measured concentrations. This may be due to production systematics or the fact that signal size and linewidth may affect the percentage of peak area contained within the integration bounds.

[0063] As is evident from Figure 3C comparing the measured LiPF6concentrations to the nominal (prepared) concentrations, for the majority of samples, the measured concentrations agree with the nominal values to within 10%. Furthermore, the relative stability or loss / leakage of electrolyte signals could be tracked through time-separated measurement of the same cells. Only samples 6 and 7 display larger deviations between nominal and measured concentrations—this may be due to production systematics or the fact that signal size and linewidth may affect the percentage of peak area contained within the integration bounds.

[0064] To test compatibility of the experimental setup and protocol not only with Al housing but also with all other components of a realistic working battery, additional coin cells of standard geometry were tested—without electrolyte but containing a copper current collector, a lithium anode, a glassfiber separator, and a lithium-nickel-manganese-cobalt-oxide (NMC811) cathode. Although the inclusion of copper material can increase the amount of background noise attributed to shuttling-induced eddy currents, this was not expected to impede measurement or characterization of electrolyte content. The baseline noise occurs at lower frequencies and resonance frequencies in the setup can be shifted out of this range through tuning of the measurement field (Figure 1A), or one can drop more initial points of the measured time-domain signal to suppress the noise.

[0065] Peaks from other manifolds (∆^^ ് 0) (i.e. the ‘J-peaks’) can also be detecteddirectly or indirectly. Indirect detection via a saturation transfer experiment can provide asensitivity enhancement, whereby the ∆^^0 transitions are resonantly irradiated by pulses ormodulated magnetic fields, and the signal changes in the much stronger ∆^^ ൌ 0 transitions aredetected. In this way, a significant enhancement can be achieved for the detection of ∆^^0transitions. This approach can further allow for the identification of chemical species and degradation products in the electrolyte.

[0066] The battery electrolyte analysis can be implemented in the study of electrolyte amounts and degradation in functioning devices, either during rest or during operation 17 4920-8416-5164Atty. Dkt. No.046434-0887 (charging / discharging). The battery electrolyte analysis can be implemented in the study of electrolyte behavior over the whole life-cycle of a cell, from fabrication (e.g., filling), formation, integration, through testing (e.g. high-stress testing), after use, testing for repurposing and recycling. The battery electrolyte analysis can be implemented in the examination of a large format cell (e.g., large compared to sensor size), where the surface of the cell is scanned. This procedure can be accomplished by first pre-polarizing the area by placing a polarizing magnet at the location, and then removing the magnet and placing a magnetometer sensor at the location and acquiring the electrolyte signals. In this way, point analysis or scanning of the whole surface of the device and obtaining location-resolved information can be performed.

[0067] Figures 4A and 4B show results from EC / DMC and LiPF6 quantification over time based on Figures 3A and 3B. Figures 4A and 4B show results from monitoring of the electrolyte peaks as a function of time, using five partitions or batches of 2000 scans (13.5 h each) from the cell with a nominal 2.5M LiPF6 concentration (sample 7). Figure 4A shows a plot of the measured spectra. Figure 4B shows a plot of solute and solvent integrals normalized to the first data point. Error bars are calculated as standard error of the partitioned integrated signals (shaded regions). The error on the proton signal is smaller than that on the ^^^^^ିsignal (relative errors of 4.4% and 1.1% for solute and solvent signals, respectively), as expected due to the smaller SNR of the latter. The electrolyte signals from this sample cell were found to be relatively stable not only over the course of the three-day measurement cycle (with minor fluctuations), but also in a second measurement taken two months later.

[0068] With these encouraging results, attention can be turned to functional pouch-cell batteries, which are most relevant for industrial applications. These pouch cells can be manufactured in-house, as commercially available miniaturized pouch cells which could fit into the bore of our prepolarizing magnet and solenoid (Figure 1A) typically contain polymer rather than liquid electrolyte (this reduces the cell weight for wearable electronics, for example). The aim was rather to test a scaled down version of standard liquid-electrolyte cells as a proof of principle. To this end, pouch cells with a 1 cm2active area were produced from commercial components, with a lithiumcobalt-oxide (LCO) film cathode, a graphite anode, and 1M LiPF6 in EC / DMC (LP30) as the electrolyte. Due to the miniscule electrolyte volume and the flat geometry of the pouch cell which did not fill the cylindrical sensitive region of the spectrometer, as well as possible electrolyte absorption into the separator or around the paramagnetic LiCoO2 cathode, only the proton solvent signal is visible above the noise. The 18 4920-8416-5164Atty. Dkt. No.046434-0887 largest PF^ିpeak appears in the calibration spectrum at 32 Hz, with an amplitude a few percent that of the proton peak, as expected for the 1M concentration. Despite this, the solvent proton signal from the cell was clearly visible at the expected frequency (Figure 5)—already sufficient to characterize the presence and potential leakage of electrolyte.

[0069] Figure 5 illustrates results from functional pouch-cell batteries, which demonstrate that they can be measured with our experimental apparatus and protocol. The spectrometer could be operated at an arbitrarily low background field—here 0.9μT, corresponding to a proton resonance frequency of 38 Hz—due to the reduced shuttling-induced baseline noise from the laminate pouch-cell casing. Plots compare recorded spectra from a 1.5mL calibration sample of industry-standard 1M LiPF6 in 50:50 EC / DMC (top panel, 256 scans), a typical pouch cell filled with 38 μL of the same electrolyte (middle panel, 10000 scans), and an empty sample vial showing the noise floor of the spectrometer (bottom panel, 10000 scans).

[0070] As a technical note, higher conductivity of metals can be associated with larger shuttling-induced eddy currents—which is likely why the less pure commercial-grade Al pouch-cell foil does not suffer from this issue. Nonmagnetic (such as Al) battery enclosures are preferred in our setup, because the particular atomic magnetometers used for detection can only operate in background fields less than ∼ 100 nT. This is not a fundamental limitation, however, since a variety of sensor options exist for operation at elevated fields and even in unshielded environments. Furthermore, the magnetometers used in this work have been shown to be compatible with common commercially available Li-ion pouch cells. Understanding the material properties of various measured battery cells is important to the design of optimized NMR experiments.

[0071] The systems and methods of the present disclosure demonstrate the ability of ultralowfield NMR spectroscopy to directly characterize battery electrolyte composition through battery housing, in a manner compatible with nondestructive operando measurements. NMR signals were recorded using atomic magnetometers, and a theoretical framework for interpretation of spectra was presented. Time-dependence of the electrolyte signals was also tracked to demonstrate relative stability or leakage of sample cells. The quantification and characterization of electrolytes is crucial for the diagnosis of battery defects and aging processes. This work can be extended to a large class of electrolytes and battery geometries beyond those examined here. Nondestructive battery diagnostics remain limited, and the addition of this method provides critical characterization capability for battery development and testing. Given the flexibility and tunability of ZULF-NMR systems. These results pave the 19 4920-8416-5164Atty. Dkt. No.046434-0887 way to measurements of larger commercial pouch or prismatic cells via adaptation of the polarizing magnet and experimental geometry.

[0072] Envisioned experimental enhancements for battery diagnostic applications include optimization of the measurement duty cycle for faster sensitive detection of electrolyte, reduction of the sensor offset distance using customized atomic magnetometers, and optimization of the shuttling field profile to maximize SNR. One may also use a superconducting magnet (∼ 20 T) for prepolarization to immediately achieve a 20-fold boost in signal (while still detecting at ultralow field) and speed up data collection by a factor of 400. Signal enhancement will also be obtained through measurement of larger volumes of electrolyte, as will be the case in the aforementioned commercial batteries. However, the ability of the method to detect even tens of µL of electrolyte suggests that spatially resolved measurement of larger batteries—through the use of multiple sensors or a scanning system— is also feasible. Protocols without mechanical shuttling might also be explored, through the use of switchable magnets or in situ polarization with a solenoid, to enable localized measurements of larger / heavier batteries.

[0073] J-peaks may also be detected directly or indirectly. Indirect detection could be enabled via prior population transfer, whereby one resonantly irradiates J-transitions and subsequently detects a signal enhancement of the nZF-peaks. Such an approach may further enable the identification of chemical species and degradation products in the electrolyte. Further diagnostic potential is attainable from measurement of spectral linewidths and relaxation rates. Cathode degradation may occur due to transition metal dissolution, and the presence of paramagnetic Ni2+ and Mn2+ ions in solution could be identified via their effect on spectral line broadening. Finally, cycling of battery cells is expected to be associated with additional degradation and consumption of the electrolyte during cycling. For example, cracking of the cathode material can expose fresh surface area with which the electrolyte reacts, thereby consuming the electrolyte and affecting the spectral signature. All these processes will require careful study to disentangle their various spectral contributions. Relaxation parameters (such as for example T1, T2, T1rho, or singlet state relaxation rates) could be encoded into the measured signals by inserting an appropriate preparation pulse sequence (including, for example waiting delays to allow relaxation to progress, and sequences that convert from nuclear triplet to singlet states). This encoding could also be achieved by adjusting adiabatic field drops from the polarization field, by allowing the spin system to transition through a well- defined field profile at well-defined speeds. This preparation would provide optimal 20 4920-8416-5164Atty. Dkt. No.046434-0887 preparations of different magnetization states, which then can be investigated with regard to their relaxation behavior. The relaxation rates can subsequently be encoded into the measured signals either as a signal or image contrast, or as a time series (signal as a function of waiting or encoding time). This approach also addresses spectral crowding or situations with insufficient resolution wherein specific resonance lines could be suppressed or enhanced based on preparation sequences and relaxation behavior.

[0074] The relaxation properties of the resonance lines could be investigated in the high, the intermediate field, and ZULF regimes to further authenticate and discriminate different components of the electrolyte, or physical properties such as diffusion and viscosity.

[0075] All diagnosis can be implemented in a spectroscopy mode (collecting spectra of the whole sensitive sample volume), or in a site-resolved manner either by scanning the surface with a polarization methodology and sensor readout technique, or by employing MRI techniques involving magnetic field gradients.

[0076] Within the framework of nondestructive measurement of electrolyte spectra through battery housing, a wide variety of ULF-NMR experimental geometries and protocols are realizable for practical diagnostic applications. The setup used here was assembled from equipment available in our labs with a total value on order 10k€; cheaper systems are also possible. Total cost and complexity of the apparatus depends largely on the choice of prepolarization magnet and detectors, but affordable commercial options exist. With these promising first steps, we look forward to many further developments in the multidisciplinary field of nondestructive battery ZULF-NMR, as a complement to other more invasive battery- diagnostic techniques.

[0077] Figure 6 illustrates a method 600 for nondestructive observation of an electrolyte in a battery. In brief summary, the method 600 can include thermally polarizing nuclear spins in a battery cell (BLOCK 605). The method 600 can include positioning the battery cell in a detection region (BLOCK 610). The method 600 can include receiving NMR signals from the electrolyte (BLOCK 615). The method 600 can include characterizing one or more properties of the electrolyte (BLOCK 620).

[0078] The method 600 can include thermally polarizing nuclear spins in a battery cell (BLOCK 605). For example, the method 600 can include thermally polarizing the battery cell in a polarization region. The polarization region can include region where the battery cell becomes thermally polarized (e.g., thermally pre-polarized). The polarization region can be 21 4920-8416-5164Atty. Dkt. No.046434-0887 defined by one or more magnets. The battery cell can be thermally polarized at 1T. The battery cell can include an electrolyte disposed in a housing. A superconducting magnet can be used for prepolarization to achieve a boost in signal (e.g., 20-fold increase) and speed up data collection (e.g., by a factor of 400). The superconducting magnet can have a field of about 20 T.

[0079] The method 600 can include positioning the battery cell in a detection region (BLOCK 610). For example, the method 600 can include shuttling the battery cell to the detection region. Shuttling can include mechanical shuttling or physically moving the battery cell from a location outside of the detection region to a location inside the detection region. In one example, the detection region includes a magnetically shielded detection region. The detection region can be defined by one or more magnetometers. For example, the detection region can be bounded by the two magnetometers. The location outside of the detection region can include the polarization region. The polarization region can be located a distance from the detection region. The polarization region can be separated from the detection region by a solenoid. The polarization region can be separated from the detection region by a portion of the magnetic shield. As an alternative to shuttling the battery cell, switchable magnets can be used to enable localized measurements of large and / or heavier batteries.

[0080] The method 600 can include receiving NMR signals from the electrolyte (BLOCK 615). Battery housing and electrodes can be transparent to electromagnetic fields involved in zero-to-ultralow-field NMR due to the reduced resonance frequencies in ZULF NMR. Quantification of the solvent and salt components of the electrolyte signature can be quantified. The NMR signals can be generated by using zero-to-ultralow-field NMR, where the resonance frequencies of nuclear-spin samples can span the range from Hz to kHz (e.g., less than hundreds of MHz). The resonance frequencies can be tunable through the application of a background field. Spin excitation can be performed using pulses of static magnetic fields. Metals can be essentially transparent to the applied and measured electromagnetic waves, allowing for characterization of the electrolyte. At the low frequencies of signals in ZULF-NMR spectroscopy compared to NMR spectroscopy at hundreds of MHz, detection can be performed using superconducting quantum-interference devices or atomic magnetometers (e.g., optically pumped magnetometers).

[0081] The method 600 can include characterizing (e.g., detecting, determining, diagnosing, quantifying, calculating) one or more properties of the electrolyte (BLOCK 620). For example, the method 600 can include detect changes or defects in the battery cell in a 22 4920-8416-5164Atty. Dkt. No.046434-0887 nondestructive way. Changes in electrolyte composition can be directed characterized. For example, the nature, distribution, and / or composition of the electrolyte can be characterized or determined. The state and composition of the electrolyte can be determined or tracked. The method 600 can include characterizing the electrolyte of the battery cell without opening or damaging the battery cell. The method 600 can include characterizing the electrolyte of the battery cell through the housing of the battery cell. In some embodiments, the method 600 includes characterizing the one or more properties of the electrolyte during operation of the battery cell. The method 600 can include quantifying the one or more properties of the electrolyte during the operation of the battery cell. For example, the method 600 can include calculating a concentration of the electrolyte in the battery cell.

[0082] The method 600 can include generating a spectra. For example, the method 600 can include generating a spectra for a regime in which ω0 << J. ω0 is a Larmor frequency of a spin system and J is a coupling constant characterizing a strength of spin-spin interaction. J-peaks can be detected directly or indirectly.

[0083] The method 600 can include diagnosing one or more defects of the battery cell using the NMR signals. The one or more defects of the battery cell can be determined based on the quantification and / or characterization of the electrolytes. The method 600 can include diagnosing one or more defects of the battery cell non-destructively. Non-destructive diagnostic techniques can be performed without damaging cell such that the battery cell can continue operation after the non-destructive diagnostic method is performed. The method 600 can include diagnosing one or more defects of the battery cell by implementing MRI.

[0084] The method 600 can include pre-polarizing a location of the battery cell. For example, the method 600 can include pre-polarization a location where the battery cell is or will be positioned. In some examples, the method 600 can include acquiring electrolyte signals from the electrolyte at the location of the battery cell. The method 600 can include pre- polarizing the battery at a specified location. For example, the method 600 can include pre- polarizing the battery at a location within the battery cell. Signals which may be used to characterize the electrolyte can be obtained at the location within the battery cell.

[0085] The method 600 can include using relaxation properties of the resonance lines in the high field and ZULF regimes to further authenticate and discriminate different components of the electrolyte, or physical properties such as diffusion and viscosity. This can be achieved by measuring the line widths and / or measuring the rate of recovery to equilibrium for different 23 4920-8416-5164Atty. Dkt. No.046434-0887 resonance lines. This approach would be particularly useful when there is spectral crowding or insufficient resolution.

[0086] The method 600 can include scanning the surface of a large-format battery with a polarizing magnet / sensor combination. This would allow for the determination of the spatial localization of the electron distribution and its state in the situation where the battery is too large to fit in the measurement setup. In this case, a localized magnetic field can be generated for pre-polarization in a given location, then the magnetic field can be removed, and a magnetic field sensor can be placed in the same area to pick up the magnetic resonance signal. This measurement could also be performed in an arrayed fashion, thereby allowing for the measurement of the electrolyte distribution and state quickly over a large surface.

[0087] The method 600 can include combining ZULF spectroscopy with an MRI approach with the help of magnetic field gradients to obtain localized electrolyte analysis. In some embodiments, the method 600 can include performing measurements in the intermediate regime (e.g., ω0 is the same order of magnitude as J), where the Larmor frequency is on the same order as the J-coupling, and even in the high field regime where the Larmor frequency is much larger than the J-coupling (ω0>> J). In some embodiments, the method 600 can include prepending the readout sequence with a saturation transfer irradiation, which allows for the transferring of the population from the J-peaks to the nZF peaks. This procedure would allow the detection of specific electrolyte with enhanced sensitivity.

[0088] The systems and methods of the present disclosure can include experiments demonstrating the ability of ultralow-field NMR spectroscopy to characterize battery electrolyte composition through battery housing, in a manner compatible with nondestructive operando measurements. NMR signals can be recorded using atomic magnetometer sensors. Time-dependence of the electrolyte signals can be tracked to demonstrate relative stability or leakage of sample cells. The quantification and characterization of electrolytes can be important for the diagnosis of battery defects and aging processes. The quantification of both LiPF6 and ethylene-carbonate / dimethyl carbonate mixtures in a typical battery housing can be demonstrated. Solvent leakage over time can be assessed by these measurements. This method can provide nondestructive battery diagnostics and characterization capability for battery development and testing.

[0089] The method can include thermally polarizing a battery cell in a polarization region, or hyperpolarizing by other methods, such as dynamic nuclear polarization, parahydrogen 24 4920-8416-5164Atty. Dkt. No.046434-0887 induced polarization, or chemically induced dynamic nuclear polarization. The battery cell can include an electrolyte disposed in a housing. The electrolyte can include at least one of ethylene carbonate or dimethyl carbonate. The electrolyte can include LiPF6. The housing can include a metal. The metal can include aluminum. The method can include positioning the battery cell in a detection region. The method can include receiving, by one or more atomic magnetometer sensors, NMR signals from the electrolyte. The NMR signals can be in a range of less than 500 Hz The method can include characterizing, using the NMR signals, one or more properties of the electrolyte. The one or more properties of the electrolyte can include at least one of electrolyte composition, electrolyte loss, electrolyte degradation, or electrolyte amount.

[0090] Embodiments of the subject matter and the operations described in this specification can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. The subject matter described in this specification can be implemented as one or more computer programs, e.g., one or more circuits of computer program instructions, encoded on one or more computer storage media for execution by, or to control the operation of, data processing apparatus. Alternatively or in addition, the program instructions can be encoded on an artificially generated propagated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal that is generated to encode information for transmission to suitable receiver apparatus for execution by a data processing apparatus. A computer storage medium can be, or be included in, a computer- readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination of one or more of them. Moreover, while a computer storage medium may not be a propagated signal, a computer storage medium can be a source or destination of computer program instructions encoded in an artificially generated propagated signal. The computer storage medium can also be, or be included in, one or more separate components or media (e.g., multiple CDs, disks, or other storage devices).

[0091] The operations described in this specification can be performed by a data processing apparatus on data stored on one or more computer-readable storage devices or received from other sources. The term “data processing apparatus” or “computing device” encompasses various apparatuses, devices, and machines for processing data, including by way of example a programmable processor, a computer, a system on a chip, or multiple ones, or combinations of the foregoing. The apparatus can include special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit). The apparatus 25 4920-8416-5164Atty. Dkt. No.046434-0887 can also include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, a cross-platform runtime environment, a virtual machine, or a combination of one or more of them. The apparatus and execution environment can realize various different computing model infrastructures, such as web services, distributed computing and grid computing infrastructures.

[0092] A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, declarative or procedural languages, and it can be deployed in any form, including as a stand-alone program or as a circuit, component, subroutine, object, or other unit suitable for use in a computing environment. A computer program may, but need not, correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more circuits, subprograms, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

[0093] Processors suitable for the execution of a computer program include, by way of example, microprocessors, and any one or more processors of a digital computer. A processor can receive instructions and data from a read-only memory or a random-access memory or both. The elements of a computer are a processor for performing actions in accordance with instructions and one or more memory devices for storing instructions and data. A computer can include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. A computer need not have such devices. Moreover, a computer can be embedded in another device, e.g., a personal digital assistant (PDA), a Global Positioning System (GPS) receiver, or a portable storage device (e.g., a universal serial bus (USB) flash drive), to name just a few. Devices suitable for storing computer program instructions and data include all forms of non- volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry. 26 4920-8416-5164Atty. Dkt. No.046434-0887

[0094] To provide for interaction with a user, implementations of the subject matter described in this specification can be implemented on a computer having a display device, e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor, for displaying information to the user and a keyboard and a pointing device, e.g., a mouse or a trackball, by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input.

[0095] The implementations described herein can be implemented in any of numerous ways including, for example, using hardware, software or a combination thereof. When implemented in software, the software code can be executed on any suitable processor or collection of processors, whether provided in a single computer or distributed among multiple computers.

[0096] Also, a computer may have one or more input and output devices. These devices can be used, among other things, to present a user interface. Examples of output devices that can be used to provide a user interface include printers or display screens for visual presentation of output and speakers or other sound generating devices for audible presentation of output. Examples of input devices that can be used for a user interface include keyboards, and pointing devices, such as mice, touch pads, and digitizing tablets. As another example, a computer may receive input information through speech recognition or in other audible format.

[0097] Such computers may be interconnected by one or more networks in any suitable form, including a local area network or a wide area network, such as an enterprise network, and intelligent network (IN) or the Internet. Such networks may be based on any suitable technology and may operate according to any suitable protocol and may include wireless networks, wired networks or fiber optic networks.

[0098] A computer employed to implement at least a portion of the functionality described herein may comprise a memory, one or more processing units (also referred to herein simply as “processors”), one or more communication interfaces, one or more display units, and one or more user input devices. The memory may comprise any computer-readable media, and may store computer instructions (also referred to herein as “processor-executable instructions”) for implementing the various functionalities described herein. The processing unit(s) may be used to execute the instructions. The communication interface(s) may be coupled to a wired or 27 4920-8416-5164Atty. Dkt. No.046434-0887 wireless network, bus, or other communication means and may therefore allow the computer to transmit communications to or receive communications from other devices. The display unit(s) may be provided, for example, to allow a user to view various information in connection with execution of the instructions. The user input device(s) may be provided, for example, to allow the user to make manual adjustments, make selections, enter data or various other information, or interact in any of a variety of manners with the processor during execution of the instructions.

[0099] The various methods or processes outlined herein may be coded as software that is executable on one or more processors that employ any one of a variety of operating systems or platforms. Additionally, such software may be written using any of a number of suitable programming languages or programming or scripting tools, and also may be compiled as executable machine language code or intermediate code that is executed on a framework or virtual machine.

[0100] In this respect, various inventive concepts may be embodied as a computer-readable storage medium (or multiple computer-readable storage media) (e.g., a computer memory, one or more floppy discs, compact discs, optical discs, magnetic tapes, flash memories, circuit configurations in Field Programmable Gate Arrays or other semiconductor devices, or other non-transitory medium or tangible computer storage medium) encoded with one or more programs that, when executed on one or more computers or other processors, perform methods that implement the various embodiments of the solution discussed above. The computer- readable medium or media can be transportable, such that the program or programs stored thereon can be loaded onto one or more different computers or other processors to implement various aspects of the present solution as discussed above.

[0101] The terms “program” or “software” are used herein to refer to any type of computer code or set of computer-executable instructions that can be employed to program a computer or other processor to implement various aspects of embodiments as discussed above. One or more computer programs that when executed perform methods of the present solution need not reside on a single computer or processor, but may be distributed in a modular fashion amongst a number of different computers or processors to implement various aspects of the present solution.

[0102] Computer-executable instructions may be in many forms, such as program modules, executed by one or more computers or other devices. Program modules can include routines, 28 4920-8416-5164Atty. Dkt. No.046434-0887 programs, objects, components, data structures, or other components that perform particular tasks or implement particular abstract data types. The functionality of the program modules can be combined or distributed as desired in various embodiments.

[0103] Also, data structures may be stored in computer-readable media in any suitable form. For simplicity of illustration, data structures may be shown to have fields that are related through location in the data structure. Such relationships may likewise be achieved by assigning storage for the fields with locations in a computer-readable medium that convey relationship between the fields. However, any suitable mechanism may be used to establish a relationship between information in fields of a data structure, including through the use of pointers, tags or other mechanisms that establish relationship between data elements.

[0104] While operations are depicted in the drawings in a particular order, such operations are not required to be performed in the particular order shown or in sequential order, and all illustrated operations are not required to be performed. Actions described herein can be performed in a different order.

[0105] Having now described some illustrative implementations, it is apparent that the foregoing is illustrative and not limiting, having been presented by way of example. In particular, although many of the examples presented herein involve specific combinations of method acts or system elements, those acts and those elements may be combined in other ways to accomplish the same objectives. Acts, elements and features discussed in connection with one implementation are not intended to be excluded from a similar role in other implementations or implementations.

[0106] The phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including” “comprising” “having” “containing” “involving” “characterized by” “characterized in that” and variations thereof herein, is meant to encompass the items listed thereafter, equivalents thereof, and additional items, as well as alternate implementations consisting of the items listed thereafter exclusively. In one implementation, the systems and methods described herein consist of one, each combination of more than one, or all of the described elements, acts, or components.

[0107] Any references to implementations or elements or acts of the systems and methods herein referred to in the singular can include implementations including a plurality of these elements, and any references in plural to any implementation or element or act herein can include implementations including only a single element. References in the singular or plural 29 4920-8416-5164Atty. Dkt. No.046434-0887 form are not intended to limit the presently disclosed systems or methods, their components, acts, or elements to single or plural configurations. References to any act or element being based on any information, act or element may include implementations where the act or element is based at least in part on any information, act, or element.

[0108] Any implementation disclosed herein may be combined with any other implementation, and references to “an implementation,” “some implementations,” “an alternate implementation,” “various implementations,” “one implementation” or the like are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described in connection with the implementation may be included in at least one implementation. Such terms as used herein are not necessarily all referring to the same implementation. Any implementation may be combined with any other implementation, inclusively or exclusively, in any manner consistent with the aspects and implementations disclosed herein.

[0109] References to “or” may be construed as inclusive so that any terms described using “or” may indicate any of a single, more than one, and all of the described terms. References to at least one of a conjunctive list of terms may be construed as an inclusive OR to indicate any of a single, more than one, and all of the described terms. For example, a reference to “at least one of ‘A’ and ‘B’” can include only ‘A’, only ‘B’, as well as both ‘A’ and ‘B’. Elements other than ‘A’ and ‘B’ can also be included.

[0110] The systems and methods described herein may be embodied in other specific forms without departing from the characteristics thereof. The foregoing implementations are illustrative rather than limiting of the described systems and methods.

[0111] Where technical features in the drawings, detailed description or any claim are followed by reference signs, the reference signs have been included to increase the intelligibility of the drawings, detailed description, and claims. Accordingly, neither the reference signs nor their absence have any limiting effect on the scope of any claim elements.

[0112] The systems and methods described herein may be embodied in other specific forms without departing from the characteristics thereof. The foregoing implementations are illustrative rather than limiting of the described systems and methods. Scope of the systems and methods described herein is thus indicated by the appended claims, rather than the foregoing description, and changes that come within the meaning and range of equivalency of the claims are embraced therein. 30 4920-8416-5164

Claims

Atty. Dkt. No.046434-0887 WHAT IS CLAIMED:

1. A method, comprising: thermally polarizing nuclear spins in a battery cell in a polarization region, the battery cell comprising an electrolyte disposed in a housing; positioning the battery cell in a detection region; receiving, by one or more atomic magnetometer sensors, NMR signals from the electrolyte; and characterizing, using the NMR signals, one or more properties of the electrolyte; wherein the one or more properties of the electrolyte comprise at least one of electrolyte composition, electrolyte loss, electrolyte degradation, or electrolyte amount.

2. The method of claim 1, comprising: generating a spectra for a regime in which ω0 << J, wherein ω0 is a Larmor frequency of a spin system and J is a coupling constant characterizing a strength of spin-spin interaction.

3. The method of claim 1, comprising: pre-polarizing a location of the battery cell; and acquiring electrolyte signals from the electrolyte at the location of the battery cell.

4. The method of claim 1, comprising: characterizing the one or more properties of the electrolyte during operation of the battery cell.

5. The method of claim 1, comprising: using relaxation properties of resonance lines to discriminate different components of the electrolyte or to determine physical properties of the electrolyte.

6. The method of claim 1, comprising: scanning a surface of a battery to determine a spatial localization of an electron distribution. 31 4920-8416-5164Atty. Dkt. No.046434-0887 7. The method of claim 1, comprising: generating a spectra for a regime in which ω0 is the same order of magnitude as J, wherein ω0is a Larmor frequency of a spin system and J is a coupling constant characterizing a strength of spin-spin interaction.

8. The method of claim 1, wherein the electrolyte comprises at least one of ethylene carbonate, dimethyl carbonate, or LiPF6.

9. The method of claim 1, comprising: diagnosing one or more defects of the battery cell using at least one of the NMR signals or by implementing MRI.

10. The method of claim 1, wherein: the NMR signals are in a range of less than 500 Hz; and the housing comprises a metal.

11. A system comprising: a magnetic shield comprising a detection region; a battery cell comprising an electrolyte disposed in a housing, the battery cell disposed in a holder, the holder disposed in the detection region; a magnet configured to thermally polarize nuclear spins in the battery cell in a polarization region; one or more atomic magnetometer sensors configured to receive NMR signals from the electrolyte; and a processor configured to characterize, using the NMR signals, one or more properties of the electrolyte disposed in the battery cell; wherein the one or more properties of the electrolyte comprise at least one of electrolyte composition, electrolyte loss, electrolyte degradation, or electrolyte amount.

12. The system of claim 11, comprising: a plurality of Helmholtz coils disposed in the detection region.

13. The system of claim 11, comprising: a solenoid disposed in the magnetic shield; wherein the battery cell is disposed in the solenoid. 32 4920-8416-5164Atty. Dkt. No.046434-0887 14. The system of claim 11, wherein the processor is configured to generate a spectra for a regime in which ω0 << J, wherein ω0 is a Larmor frequency of a spin system and J is a coupling constant characterizing a strength of spin-spin interaction.

15. The system of claim 11, wherein the NMR signals are in a range of less than 500 Hz.

16. The system of claim 11, wherein the housing comprises a metal.

17. The system of claim 11, wherein the electrolyte comprises at least one of ethylene carbonate or dimethyl carbonate.

18. The system of claim 11, wherein the processor is configured to diagnose one or more defects of the battery cell using the NMR signals.

19. The system of claim 11, wherein the processor is configured to characterize the one or more properties of the electrolyte during operation of the battery cell.

20. The system of claim 11, wherein the processor is configured to: pre-polarize a location of the battery cell; and acquire electrolyte signals from the electrolyte at the location of the battery cell. 33 4920-8416-5164

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