Method and apparatus for characterization of electrochemical systems by acousto-voltammetry

Abstract

Described herein is a methodology for performing an electrochemically resolved acoustic emissions analysis using acousto-voltammetry on, e.g., Li-ion batteries to identify microscale processes, using graphite and Ni0.8Mn0.1Co0.1O2 (NMC811) electrodes as case studies. First, elimination of electromagnetic interference improved reproducibility in the number and cumulative energy of acoustic emissions per cycle. Next, acousto-voltammetry, or the measurement of acoustic emissions during cyclic voltammetry, of Li-ion batteries allowed for a direct correlation between acoustic activity and specific battery processes, such as gas generation during SEI formation and particle fracture during NMC811 (de)lithiation. Finally, signal processing using the wavelet transform assisted in distinguishing acoustic emissions from different battery processes using multi-resolution features and unsupervised clustering.

Description

mit-26171pctMETHOD AND APPARATUS FOR CHARACTERIZATION OF ELECTROCHEMICAL SYSTEMS BY ACOUSTO-VOLTAMMETRYRELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 704,005, filed 6 October 2025.BACKGROUND

[0002] The discussion of the background state of the art below may reflect hindsight gained from the disclosed invention(s), and these characterizations are not necessarily admitted to be prior art.

[0003] Li-ion batteries (LIBs) are ubiquitous energy storage devices for consumer electronics and the dominant choice for electric vehicle energy storage. This is possible due to the high energy density and low self-discharge of these systems. While their long lifetime is praised as well, several degradation mechanisms are known to occur to vary ing degrees based on electrode material, electrolyte, cycling protocol, and environmental factors. A focus over the last few decades has been to develop techniques that can monitor the state-of-health (SoH) or state-o f-safety (SoS) of a cell and that incorporate more information about the (micro)structural condition of the internal components.

[0004] Ideal battery diagnostic techniques are non-destructive, allowing for an assessment without damaging the system. A few non-destructive methods already exist, including: (1) electrochemical techniques, such as electrochemical impedance spectroscopy (EIS) and hybrid pulse power characterization, (2) thermal techniques, such as infrared thermography (IRT), (3) imaging techniques, such as X-ray computed tomography (XCT), neutron imaging, and ultrasonic testing. Each method has advantages and disadvantages in terms of cost, accuracy, time required, sensitivity, and ability to be performed in operando.

[0005] Another popular non-destructive evaluation technique is acoustic emission (AE) testing. Acoustic emissions are elastic waves that are generated by a release of energy in a material due to a redistribution of stress caused by a change in internal structure. The technique has predominantly been demonstrated for the monitoring of large cement or metal structures, and has been show n to be sensitive to material fracture, deformation, corrosion, and gas evolution. Historically, the number of acoustic emissions and the maximum amplitude of acoustic-emission signals have been used to estimate the amount of damage in the target structure. Source localization of an acoustic emission has also been accomplished by reconciling the arrival time differences of the waveform at distinct sensors on the structure. Acoustic-emission testing shares similarities with ultrasonic techniques through the shared use of acoustic activity; however, the distinction lies in the purely passive monitoring of acoustic w aves for the former, while the latter requires the active input of a signal into themit-26171pctsystem to calculate the elastic modulus by monitoring the reflection or transmission of the wave.

[0006] Modem acoustic-emission testing began in the early 1950s with comprehensive acoustic measurements of metallic materials under a range of tensile stresses using a piezomicrophone. The earliest uses of acoustic-emission measurements for electrochemical systems were to monitor ion transport through materials, specifically of sodium ions through a P-Al solid electrolyte for Na-S batteries and the electrochemical transformation of Al into -LiAl. The first study involving operando acoustic-emission testing of Li-metal batteries was published in 1997, when T. Ohzuku, et al., Monitoring of Particle Fracture by Acoustic Emission during Charge and Discharge of Li / MnCh Cells / ’ 144 J. Electrochem. Soc. 3496-3500 (1997) measured the acoustic activity during cycling of a Li || MnCh cell. Soon after, more acoustic-emission studies on materials for batteries, including PbSiOs, SnSiCh. and graphite, were explored. In the decade that followed, careful acoustic-emission studies of electrochemical processes, such as corrosion, deposition, and gas evolution, were conducted, as well as of electrode materials for Ni-MH batteries. Acoustic emissions during cycling or accelerated degradation testing of half-cell and full-cell Li-ion batteries were then studied. A wide collection of anode materials, such as graphite, silicon, lithium titanium oxide (LTO), and high-entropy oxides (Coo.2Cuo.2Mgo2Nio.2Zno.2) were investigated along with several types of cathode materials, including lithium cobalt oxide (LCO), lithium nickel oxide (LNO), lithium manganese oxide (LMO), high-entropy oxides (LityCoo.2Cuo.2Mgo.2Nio.2Zno.2)OFA), nickel-antimony (NiSb2), sulfur, nickel manganese cobalt oxide (NMC), and material hybrids using acoustic-emission testing. Moreover, commercial Li-ion batteries with undisclosed electrode materials and additional work on nickel-metal hydride (Ni-MH) cells have also been studied using operando acoustic-emission testing. Finally, acoustic-emission analyses have been used for mechanical failure and external short circuit testing of Li-ion batteries.

[0007] Recently, a few acoustic-emission studies on Li-ion batteries have seen a correlation between acoustic-emission data and SoH or remaining useful life, but offer little explanation as to the interpretation of the acoustic data. One possible explanation for this shortcoming is the lack of reproducibility in battery -acoustic-emission data. Distinct studies measuring acoustic activity in batteries with seemingly identical materials and cycling procedures have shown cumulative Acoustic emissions that differ by orders of magnitude. Furthermore, only a limited number of publications report data from more than one battery-acoustic-emission experiment, and those that do have high cell-to-cell variability. In additional studies, at least two cells with the same electrode material, construction, and similar testing procedure produced a fairly consistent number (within a factor of 3) of acoustic emissions.

[0008] Another challenge in the field is correlating acoustic emissions to specific processes that occur in Li-ion batteries. Electrode events, such as Li (de)intercalation, solid electrolytemit-26171pctinterphase (SEI) formation, Li plating, and particle fracture, often occur at similar voltage and time windows. The simultaneous nature of these processes is especially difficult to decouple using conventional constant current cycling, in which the exact distribution of electrons to each process cannot be easily determined through common battery experimental techniques. Using th eon and computational approaches to model these processes could assist, but they are still in developmental stages. Historically in acoustic emission literature, processes of interest are distinguished from each other and from noise by clustering methods based on features from transient acoustic emission signal data. Most have used features based on frequency analysis, such as peak frequency, average frequency, and partial power intervals; some have used time-based features, such as rise time and duration; and other have incorporated acoustic energy or amplitude. Previous battery-acoustic-emission studies have attempted to use similar analysis with some success, but have often struggled to distinctly correlate a group of acoustic emissions to specific processes or to classify all acoustic emissions.SUMMARY

[0009] This Summary introduces a selection of concepts in simplified form that are described further below in the Detailed Description. This Summary neither identifies key nor essential features, nor limits the scope of the claimed subject matter.

[0010] One aspect of the disclosure herein is an apparatus for analyzing an electrochemical system, including an anode, a cathode, an electrolyte, sensors to simultaneously record (i) acoustic emissions and (ii) electrochemical data (current, charge and / or voltage), and a signal processing system to correlate the acoustic-emission and electrochemical data to gain useful information about the internal state of the electrochemical system.

[0011] The potential control in a cyclic voltammetry (CV) or linear sweep voltammetry (LSV) assists in temporal separation of batters' mechanisms. For example, solid electrolyte interphase (SEI) formation on a graphite electrode, which is known to occur between 0.3 and 0.8 V versus Li / Li+for an ethylene carbonate-based electrolyte, and (de)lithiation, of which more than 90% of the intercalation or deintercalation of Li-ions occurs within the range of 0 to 0.2 V versus Li / Li+, predominantly occur in different potential ranges. Using voltammetry, these mechanisms are more easily isolated.

[0012] In one embodiment of the disclosed apparatus, transient acoustic-emission signals (e.g., amplitude, duration, energy', waveform, and / or frequency content) are recorded and analyzed.

[0013] In one embodiment of the disclosed apparatus, acoustic-emission transient signals are processed to extract frequency and time information, e.g., using a Wavelet or short-time Fourier transform, in order to gain more detailed information about the electrochemical system.mit-26171pct

[0014] In one embodiment of the disclosed apparatus, the electrochemical data is from cyclic voltammetry7(CV) or linear sweep voltammetry' (LSV)

[0015] In one embodiment of the disclosed apparatus, the electrochemical data is from electrochemical impedance spectroscopy (EIS)

[0016] In one embodiment of the disclosed apparatus, the electrochemical data is from potentiostatic or galvanostatic intermittent titration (PITT, GITT).

[0017] In one embodiment of the disclosed apparatus, the information about the electrochemical system comprises a state of health, remaining useful life, and / or state of safety of the electrochemical system.

[0018] In one embodiment of the disclosed apparatus, correlating the signals with the outcome of a process comprises electrochemically resolving the acoustic emissions to identify specific mechanisms within the electrochemical system.

[0019] In one embodiment of the disclosed apparatus, the information about the outcome of a process comprises solid fracture, interfacial corrosion, frictional sliding, or bubble (gas) formation, or other physical processes associated with material changes or degradation of the electrochemical system.

[0020] In one embodiment of the disclosed apparatus, the electrochemical system comprises a battery'.

[0021] In one embodiment of the disclosed apparatus, the battery is a lithium-ion battery'.

[0022] In one embodiment of the disclosed apparatus, the battery' is a solid-state battery.

[0023] In one embodiment of the disclosed apparatus, the battery^ is a flow battery.

[0024] In one embodiment of the disclosed apparatus, the electrochemical system is a fuel cell.

[0025] In one embodiment of the disclosed apparatus, the fuel cell is a proton-exchange membrane fuel cell.

[0026] In one embodiment of the disclosed apparatus, the fuel cell is a solid-oxide fuel cell.

[0027] In one embodiment of the disclosed apparatus, the electrochemical system is an electrolyzer.

[0028] In one embodiment of the disclosed apparatus, the electrolyzer produces hydrogen or carbon dioxide.

[0029] In one embodiment of the disclosed apparatus, acoustic-emission detection is performed using piezoelectric acoustic sensors.

[0030] In one embodiment of the disclosed apparatus, the signals comprise spatially varied acoustic emissions.

[0031] In one embodiment, the disclosed apparatus further comprises electromagnetic interference chokes and shielding to eliminate spurious acoustic-emission signals and / or improve signal detection.mit-26171pct

[0032] In one embodiment, the disclosed apparatus further comprises ferrite beads and / or toroids and Faraday cages to improve spurious signal removal and true signal detection.

[0033] One aspect of the disclosure herein is a method of analyzing an electrochemical system, including an anode, a cathode, and an electrolyte, the method comprising simultaneously recording acoustic emissions and electrochemical data (current, charge, and / or voltage), and identifying correlations between acoustic emissions and the electrochemical data to infer internal processes or mechanisms to gain information about the electrochemical system.

[0034] In one embodiment of the disclosed method, transient acoustic-emission signals (e.g, amplitude, duration, energy, waveform, and / or frequency content) are recorded and analyzed.

[0035] In one embodiment of the disclosed method, acoustic-emission transient signals are processed to extract frequency and time information, e.g.. using a wavelet or short-time Fourier transform, in order to gain more detailed information about the electrochemical system.

[0036] In one embodiment of the disclosed method, the electrochemical data is from cyclic voltammetry (CV) or linear sweep voltammetry (LSV).

[0037] In one embodiment of the disclosed method, the electrochemical data is from electrochemical impedance spectroscopy (EIS).

[0038] In one embodiment of the disclosed method, the electrochemical data is from potentiostatic or galvanostatic intermittent titration (PITT, GITT).

[0039] In one embodiment of the disclosed method, the information about the electrochemical system comprises a state of health, remaining useful life, and / or state of safety of the electrochemical system.

[0040] In one embodiment of the disclosed method, correlating the signals with an outcome of a process comprises electrochemically resolving the acoustic emissions to identify specific mechanisms within the electrochemical system.

[0041] In one embodiment of the disclosed method, the information about the outcome of a process comprises solid fracture, interfacial corrosion, frictional sliding, or bubble (gas) formation, or other physical processes associated with material changes or degradation of the electrochemical system.

[0042] In one embodiment of the disclosed method, the electrochemical system is a battery'.

[0043] In one embodiment of the disclosed method, the battery is a lithium-ion battery.

[0044] In one embodiment of the disclosed method, the battery is a solid-state battery7.

[0045] In one embodiment of the disclosed method, the battery7is a flow battery7.

[0046] In one embodiment of the disclosed method, the electrochemical system is a fuel cell.

[0047] In one embodiment of the disclosed method, the fuel cell is a proton-exchange membrane fuel cell.

[0048] In one embodiment of the disclosed method, the fuel cell is a solid-oxide fuel cell.mit-26171pct

[0049] In one embodiment of the disclosed method, the electrochemical system is an electrolyzer.

[0050] In one embodiment of the disclosed method, the electrolyzer produces hydrogen or carbon dioxide.

[0051] In one embodiment of the disclosed method, the acoustic-emission detection is performed using piezoelectric acoustic sensors.

[0052] In one embodiment of the disclosed method, the signals comprise spatially varied acoustic emissions.

[0053] One aspect of the disclosure herein is a quality control system comprising the disclosed apparatus.

[0054] In one embodiment, the disclosed quality control system comprises detecting defects in the structure.

[0055] In one embodiment, the disclosed quality control system comprises detecting contamination or degradation in the electrodes or electrolyte.

[0056] In one embodiment of the disclosed quality control system, the structure comprises contaminated graphite.

[0057] In one embodiment, the disclosed quality control system further comprises detecting and removing defects from the electrodes or electrolyte.

[0058] In one embodiment, the disclosed quality control system further comprises measuring the health state, the remaining useful life, or the state of safety of a battery.

[0059] In one embodiment, the disclosed quality control system is used in battery cell manufacturing.

[0060] In particular exemplifications, the system and methodology are used to perform an electrochemically resolved acoustic emissions analysis using acousto-voltammetry on Li-ion batteries to identify microscale processes, using graphite and Nio.8Mno.1Coo.1O2 (NMC811) electrodes as case studies. First, elimination of electromagnetic interference improved reproducibility in the number and cumulative energy of acoustic emissions per cycle. Next, acousto-voltammetry, or the measurement of acoustic emissions during cyclic voltammetry, of Li-ion batteries allowed for a direct correlation between acoustic activity and specific battery processes, such as gas generation during SEI formation and particle fracture during NMC811 (de)lithiation. Finally, signal processing using the wavelet transform assisted in distinguishing acoustic emissions from different battery processes using multi-resolution features and unsupervised clustering.

[0061] The following Detailed Description references the accompanying drawings, which form a part of this application, and which show, by way of illustration, specific example implementations. Other implementations may be made without departing from the scope of the disclosure.mit-26171pctBRIEF DESCRIPTION OF THE DRAWINGS

[0062] FIG. 1 is a side-view diagram of a custom configuration for performing acoustovoltammetry experiments with an acoustic-emission sensor 12 on coin cell batteries 10. A ferrite bead 18 is used as an electromagnetic interference (EMI) choke.

[0063] FIG. 2 includes plots of three separate acousto-voltammetry experiments using battery half cells with a lithium nickel manganese cobalt oxide (NMC) cathode with a high-energy ratio of 80% nickel, 10% manganese, and 10% cobalt (known as NMC 811) with identical protocols performed without EMI chokes or filters on the duration or counts of each acoustic emission.

[0064] FIG. 3 includes plots of acousto-voltammetry experiments of NMC and graphite halfcells at different scan rates. Traces of the same pattern represent experiments with the same material and CV scan rate.

[0065] FIG. 4 plots electrochemically resolved acoustic emissions of an NMC811 half-cell during 4 consecutive cyclic voltammograms conducted at a scan rate of 0.05 mV / s between 3.0 and 4.5 V. The upper histogram indicates the number of acoustic emissions detected at each potential during deintercalation of Li ions from the NMC811 cathode. The lower histogram shows the number of acoustic emissions detected at each potential during intercalation of NMC811. The cyclic voltammograms are shown by the traces.

[0066] FIG. 5 plots an operctndo XRD analysis of aNMC811 half-cell during a C / 10 constant current charge and discharge, showing that the potential regions of greatest acoustic activity during delithiation (first shading) and lithiation (second shading) occur during c-lattice contraction of the material.

[0067] FIG. 6 plots electrochemically resolved acoustic emissions ofthe NMC811 half-cell from FIGS. 2 and 3 in a first cycle.

[0068] FIG. 7 plots electrochemically resolved acoustic emissions ofthe NMC811 half-cell from FIGS. 2 and 3 in a second cycle.

[0069] FIG. 8 plots electrochemically resolved acoustic emissions ofthe NMC811 half-cell from FIGS. 2 and 3 in a third cycle.

[0070] FIG. 9 plots electrochemically resolved acoustic emissions oftheNMC811 half-cell from FIGS. 2 and 3 in a fourth cycle.

[0071] FIG. 10 plots electrochemically resolved acoustic emissions of anNMC811 half-cell at a scan rate of 0.25 mV / s.

[0072] FIG. 11 plots electrochemically resolved acoustic emissions of an NMC811 half-cell at a scan rate of 0.50 mV / s.

[0073] FIG. 12 plots electrochemically resolved acoustic emissions of an NMC811 half-cell at a scan rate of 1.0 mV / s.

[0074] FIG. 13 plots the ratio of cracked-surface NMC811 particles to total number of surface NMC811 particles calculated over at least 3 images for each of 3 cells at eachmit-26171pctpotential shown across the first CV. Only particles above 10 pm in their largest dimension were considered for the analysis.

[0075] FIG. 14 plots the rate of NMC811 particle cracking calculated using the cracked particle ratio and the scan rate. Each value represents the linear interpolation of the rate as the midpoint between potentials with cracked particle ratios. The line graph represents the absolute value of the cracked particle rate during lithiation and delithiation of NMC811. The bars are a histogram of the first cycle acoustic emissions during an acousto-voltammogram of NMC811.

[0076] FIG. 15 is a scanning-electron-microscope (SEM) image of a NMC811 electrode cycled to 3.6V.

[0077] FIG. 16 is an SEM image of aNMCSl 1 electrode cycled to 4.5V.

[0078] FIG. 17 is an SEM image of aNMC811 electrode cycled up to 4.5V and back to 3.0V.

[0079] FIG. 18 plots electrochemically resolved acoustic emissions of a polycrystalline NMC532 half-cell.

[0080] FIG. 19 plots electrochemically resolved acoustic emissions of a single crystal NMC532 half-cell.

[0081] FIG. 20 is an SEM image of a pristine poly crystalline NMC532 electrode.

[0082] FIG. 21 is an SEM image of pristine NMC532-SC electrode.

[0083] FIG. 22 is an SEM image of a cycled NMC532 electrode.

[0084] FIG. 23 is an SEM image of a cycled NMC532-SC electrode.

[0085] FIG. 24 plots electrochemically resolved acoustic emissions of a graphite half-cell during 3 consecutive cyclic voltammograms conducted at a scan rate of 0.05 mV / s between 0.01 and 1.5 V.

[0086] FIG. 25 plots electrochemically resolved acoustic emissions of the graphite half-cell from FIG. 24 during a first cycle.

[0087] FIG. 26 plots electrochemically resolved acoustic emissions of the graphite half-cell from FIG. 24 during a second cycle.

[0088] FIG. 27 plots electrochemically resolved acoustic emissions of the graphite half-cell from FIG. 24 during a third cycle.

[0089] FIG. 28 is an SEM image of a pristine graphite electrode.

[0090] FIG. 29 is an SEM image of a pristine single graphite particle.

[0091] FIG. 30 plots online electrochemical mass spectrometry data of gas evolution rate during graphite formation by cyclic voltammetry7.

[0092] FIG. 31 is a multidimensional scaling (MDS) plot of the wavelet-transformed emissions from different acousto-voltammetry experiments and noise sources. The noise emissions were captured without EMI chokes, count or duration filters, or batteries present.mit-26171pct

[0093] FIG. 32 is a MDS of wavelet-transformed emissions after the application of count and duration filters.

[0094] FIG. 33 is a sectional view of a Li-ion battery 10 including a casing 28 containing two electrodes (an anode 32 formed of graphite and a cathode 34 formed of LiCoCh) immersed in a electrolyte 38 and with a separator 36, through which Li+ions 40 can pass, separating the anode 32 from the cathode 34. The anode 32 and the cathode 34 are electrically coupled with a voltage source 30 configured to generate opposing charges on the anode 32 and the cathode 34.

[0095] In the accompanying drawings, like reference characters refer to the same or similar parts throughout the different views; and apostrophes are used to differentiate multiple instances of the same item or different embodiments of items sharing the same reference numeral. The drawings are not necessarily to scale; instead, an emphasis is placed on illustrating particular principles in the exemplifications discussed below.DETAILED DESCRIPTION

[0096] The foregoing and other features and advantages of various aspects of the invention(s) will be apparent from the following more particular description of various concepts and specific embodiments within the broader bounds of the invention, as defined by the claims. Various aspects of the subject matter introduced above and discussed in greater detail below may be implemented in any of numerous ways, as the subject matter is not limited to any particular manner of implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes.

[0097] Unless otherwise herein defined, used, or characterized, terms that are used herein (including technical and scientific terms) are to be interpreted as having a meaning that is consistent with their accepted meaning in the context of the relevant art and are not to be interpreted in an idealized or overly formal sense unless expressly so defined herein. For example, if a particular composition is referenced, the composition may be substantially (though not perfectly) pure, as practical and imperfect realities may apply; e.g., the potential presence of at least trace impurities (e.g., at less than 1 or 2%) can be understood as being within the scope of the description. Likewise, if a particular shape is referenced, the shape is intended to include imperfect variations from ideal shapes, e.g., due to manufacturing tolerances. Percentages or concentrations expressed herein can be in terms of weight or volume. Processes, procedures, and phenomena described below can occur at ambient pressure (e.g., about 50-120 kPa — for example, about 90-110 kPa) and temperature (e.g, -20 to 50°C — for example, about 10-35°C) unless otherwise specified.

[0098] Although the terms, first, second, third, etc., may be used herein to describe various elements, these elements are not to be limited by these terms. These terms are simply used to distinguish one element from another. Thus, a first element, discussed below, could bemit-26171pcttermed a second element without departing from the teachings of the exemplary embodiments.

[0099] Spatially relative terms, such as “above,’’ “below,” “left,” “right,” “in front,” “behind,” and the like, may be used herein for ease of description to describe the relationship of one element to another element, as illustrated in the figures. It will be understood that the spatially relative terms, as well as the illustrated configurations, are intended to encompass different orientations of the apparatus in use or operation in addition to the orientations described herein and depicted in the figures. For example, if the apparatus in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be onented “above” the other elements or features. Thus, the exemplary term “above” may encompass both an orientation of above and below. The apparatus may be otherwise oriented (e.g, rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. The term “about” can mean within ±10% of the value recited. In addition, where a range of values is provided, each subrange and each individual value between the upper and lower ends of the range is contemplated and, therefore, disclosed.

[0100] Further still, in this disclosure, when an element is referred to as being “on,” “connected to,” “coupled to,” “in contact with,” etc., another element, it may be directly on, connected to, coupled to, or in contact with the other element or intervening elements may be present unless otherwise specified.

[0101] Some of the terminology used herein is associated with particular embodiments and is not intended to limit more generic exemplifications of the invention. As used herein, singular forms, such as those introduced with the articles, “a” and “an,” are intended to include the plural forms as well, unless the context indicates otherwise. Additionally, the terms “includes,” “including,” “comprises,” and “comprising,” specify the presence of the stated elements or steps but do not preclude the presence or addition of one or more other elements or steps.

[0102] Additionally, the various components identified herein can be provided in an assembled and finished form; or some or all of the components can be packaged together and marketed as a kit with instructions (e.g, in written, video, or audio form) for assembly and / or modification by a customer to produce a finished product.

[0103] A lithium-ion battery 10, as is schematically illustrated in FIG. 33, includes a casing 28 in which a bath of electrolyte liquid 38 is contained. Alternatively, the electrolyte 38 can be in solid form (e.g., in the form of a solid polymer). An anode 32 (formed, e.g, of graphite) is mounted in the electrolyte 38 on one side of the chamber defined by the casing 28, while a cathode 34 (formed, e.g, of LiCoCh) is mounted in the electrolyte 38 on an opposite side of the chamber. A separator 36, which can be in the form of a microporous polymer membrane (e.g, a three-layer membrane comprising respective microporous a polyethylene layermit-26171pctsandwiched between polypropylene layers), through which lithium ions 40 can selectively pass, is mounted in the electrolyte 38 between the anode 32 and the cathode 34. As shown, the conductive pathways of an electric circuit, which can include a load, are attached to the anode 32 and to the cathode 34 and to a voltage source 30, wherein the voltage source drives electron flow from the anode 32 through the electrical circuit to the cathode 34.

[0104] In other embodiments, the methods and apparatus can be practiced or implemented with another type of electrochemical system, such as an electrolyzer, that includes the same or similar components as a battery, such as an anode, a cathode, an electrolyte, a voltage source, etc.

[0105] Herein, we descnbe a technique termed acousto-voltammetry, in which battery-acoustic-emission testing is performed simultaneously with cyclic voltammetry or linear sweep voltammetry (LSV) in order to electrochemically-resolve acoustic emissions from specific battery mechanisms. Linear sweep voltammetry' is a process in which the potential between the working electrode and a reference (or counter) electrode is swept linearly in time in one direction while the resulting current is recorded. Cyclic voltammetry is a similar process in which the potential is swept linearly between two limits in a forward and reverse direction to produce cyclic scans. This process may be repeated multiple times. Two acousto-voltammetry7case studies using graphite and NMC electrodes in Li-ion half-cell batteries are presented, along with methods to improve reproducibility7in battery -acoustic-emission experiments. Quantitative particle fracture analysis by scanning electron microscopy (SEM), comparison to gas evolution data from literature, and control experiments with Li-symmetric cells are used to corroborate battery mechanism identification. Finally, we show that unsupervised clustering techniques using features drawn from the wavelet transform (WT) allow for interpretability and distinguishability between acoustic-emission waveforms caused by graphite electrodes, NMC electrodes, and noise.

[0106] Experimental:

[0107] Cell Fabrication:

[0108] Hohsen CR2032 coin cells were used for all experiments. Cells were assembled in an Ar-filled glovebox (H2O < 0.1 ppm, O2 < 1 ppm). A lithium-nickel-manganese-cobalt-oxide (NMC) cathode with a ratio of 80% nickel, 10% manganese, and 10% cobalt (known as NMC811, available as NANOMYTE BE-56E from NEI Corp.), an NMC cathode with a ratio of 50% nickel, 30% manganese, and 20% cobalt (known as NMC532, available as NANOMYTE BE-52E from NEI Corp ), NMC532 single crystal (from LiFun Technology Co., 2.4-2.5 mAh / cm2areal capacity), an NMC cathode with an even ratio of one-third each of nickel, manganese, and cobalt (known as NMC 111, available as NANOMITE BE-50E from NEI Corp.), and graphite electrode (available as NANOMYTE BE-200E from NEI Corp.) were cut into a circular shape with a 15.9-mm diameter and paired with a 15.6-mmmit-26171pctdiameter Li-foil disk (0.45-mm thickness, available from Guangdong Canrd New Energy' Technology' Co.). The positive and negative electrodes were separated by two 19-mm diameter CELGARD 2325 separators (from Celgard, LLC). A total of 51 pL of electrolyte (1 M LiPFe in 1:1 ethylene carbonate : ethyl methyl carbonate (EC:EMC) from Sigma Aldrich) were added to each cell in three separate 17-pL aliquots, between the separators and between each separator and its adj acent electrode.

[0109] Electrochemical Characterization:

[0110] The potential window for electrochemical testing was chosen based on the known stability window of each material. The potential window was between 3.0 V and 4.5 V for Li || NMC811 and Li || NMC532 single crystal half-cells, between 3.0 V and 4.6 V for Li || NMC532 half-cells, and between 0.01 and 1.5 V for Li || graphite half-cells [all potentials are referenced herein versus (vs.) Li / Li+as a redox-couple potential set at 0 V],

[0111] All electrochemical testing was conducted using an ARBIN LBT20084 battery’ cycler (from Arbin Instruments). NMC half-cells were tap charged to 3.0 V within one hour of construction and held at that potential for 20 hours to ensure complete wetting. Graphite half-cells were tap charged to 1.5 V and held for the same period of time. Cyclic voltammetry was performed at varied scan rates in the range of 0.05 to 1 mV / s across the specified voltage range. Each cell was cycled for at least 3 cyclic voltammograms.

[0112] Acoustic Emissions Experimental Configuration:

[0113] During electrochemical testing, each cell w as monitored using a single-ended wideband-frequency acoustic-emissions sensor (WSa 100-1000 kHz acoustic-emission sensor from Physical Acoustics Corp ). A custom experimental configuration was designed to keep the acoustic-emission sensor 12 in continuous direct contact with the positive electrode case of the coin cell battery 10 (see FIG. 1). This was accomplished by designing and constructing an acrylic housing (casing) 16 to contain the acoustic-emission sensor 12 and a spring 14 that forces the sensor 12 into close contact with the battery 10. The acrylic housing 16 allowed for repeatable alignment and x-y immobilization of the acoustic-emission sensor 12 and provided (in cooperation with the spring 14) a downward pressure to ensure continuous direct contact with the coin cell battery 10. An acoustic couplant gel (an ECHO 8 ZH gel from Echo Ultrasonics) was placed on the surface of the coin cell battery 10 prior to placement of the acoustic-emission sensor 12 to prevent air gaps betw een the acrylic casing 16 of the battery’ 10 and the acoustic-emission sensor 12. The coin cell battery’ 10 w as held in place under the acoustic-emission sensor 12 using a battery’ holder 17 (a 1057TR holder from Keystone Electronics), which was connected to an ARBIN LBT20084 channel, allowing for simultaneous electrochemical and acoustic emissions testing, as is described below’. In other embodiments, the battery can be replaced with another electrochemical system, such as an electrolyzer.mit-26171pct

[0114] Also shown are electrochemical test leads 13 of a battery cycler integrated with an electrochemical impedance spectroscopy (EIS) system that is configured for evaluating the internal operational characteristics of the battery 10. The system includes an EIS analyzer electrically coupled to the battery 10 through the electrochemical test leads 13 arranged, e.g., in a four-terminal, or Kelvin, configuration. A first pair of current-carrying leads is connected to the positive and negative terminals of the battery for delivering a low-amplitude alternating current excitation signal over a range of frequencies. A second pair of high-impedance voltage sense leads is connected to the same terminals at points proximate to the battery housing so as to measure the instantaneous voltage response of the battery independent of voltage drops across the current leads. The EIS analyzer records the frequency-dependent impedance of the batten’ based on the measured voltage response and the applied current. Because the measured impedance arises from the electrochemical reactions within the electrodes and electrolyte, the frequency response can be correlated with specific chemical processes, including ion transport through the electrolyte, charge-transfer kinetics at the electrode-electrolyte interface, double-layer charging at the electrode surfaces, and diffusion of reactive species within the electrode structure. By isolating the voltage measurement from the current path, the configuration eliminates artifacts attributable to lead resistance and inductance, thereby enabling accurate identification of electrochemical behaviors that reflect the chemical state and performance of the battery7.

[0115] The acoustic-emission sensor 12 was connected to an in-line 2 / 4 / 6 preamplifier 22 (a 2 / 4 / 6 - switch-selectable gain single-ended and differential preamplifier from Mistras Group, Inc.) that was used with a single-ended configuration and again of 60 dB. The preamplifier 22 had a built-in band-pass filter that restricted the observed frequency from 10 to 900 kHz. A data acquisition system 26 (an EXPRESS-8 DAS - PCI EXPRESS-based eight-channel acoustic-emission (AE) board & system from Physical Acoustics Corp.) was connected to the output of the preamplifier 22. The AEWIN program for EXPRESS-8 software (Physical Acoustics Corp.) was used for initial acquisition, recording, and initial processing of the data.

[0116] The amplitude of each acoustic emission was calculated with Equation 1, below, where Vref = 1 pV. Acoustic emissions detected with a duration less than 3 ps or greater than 250 ps and acoustic emissions with less than 2 counts were removed from the analysis. Hits measured on multiple channels within the same 10-ms window were also removed.dB = 20 log (Vmax I Vref) - (Preamplifier Gain in dB) (1)

[0117] An acoustic noise survey of the room was initially performed with the sensors resting on empty coin-cell casings. A threshold value of 26 dB was sufficient to eliminate nearly all acoustic activity over the course of days, including events such as the opening and closing of nearby doors and foot traffic near the experiment. To demonstrate reproducibility, at least three cells with the same electrode material, coin-cell construction (metallicmit-26171pctcomponents, separator, and electrolyte), and cycling condition (electrochemical procedure, scan rate, and voltage range) were tested for each result at separate times.

[0118] In order to remove the influence of electromagnetic interference (EMI) on the battery-acoustic-emission measurements, EMI chokes, such as ferrite beads 18 and toroids, were added to all exposed current-carrying elements within 2 meters of the experiment. These current-carrying elements included the electrical connection 24 from the circuit board to the battery cycler 20, all power-supply cables, electrical wires between the battery cycler 20 (which tests the battery by repeatedly charging and discharged under controlled conditions while studying the battery’s performance to assess its condition) and the electrical connection 24 of the experimental configuration, and connections between the acoustic-emission sensor, preamplifier, and the acoustic hardware. Furthermore, a Faraday cage was constructed around the battery cycler 20. Prior to adding the EMI chokes and Faraday cage, acoustic emissions detected by the experimental configuration caused by turning the lights on and off (without a battery’ present) were recorded.

[0119] Acoustic Waveform Analysis:

[0120] A wavelet transform (WT) w as conducted on each acoustic emission w aveform. A time window of 200 ps was used for each waveform and adjusted so that the maximum power of the wave occurred at 20 ps. The algorithm was conducted using a Morlet wavelet with center and bandwidth frequencies of 1.5. The transform was conducted over the frequency range of roughly 50 kHz to 2.1 MHz. A distance matrix composed of pairwise root-mean-square distances between each transformed waveform was calculated.Multidimensional scaling, an unsupervised learning algorithm, was used to reduce the dimensionality of the distance matrix to two and to quantitatively assess the similarity of different waveforms.

[0121] Scanning Electron Microscopy:

[0122] Scanning electron microscopy (SEM) was done on a Zeiss MERLIN high-resolution SEM. Images were taken with an accelerating voltage of 15 kV and a current of 7-10 nA. Samples were prepared in an Ar glovebox and kept in an airtight container under Ar until loading onto the SEM stage (< 1 minute exposure to air).

[0123] NMC811 Particle Fracture Analysis:

[0124] Li || NMC811 half-cells were cycled at 0.05 mV / s to different potentials along the first cyclic voltammogram before disassembling the cells in an Ar glovebox and extracting the NMC811 electrodes. Three cells were cycled to each potential. Each electrode was carefully w ashed with 150 pL of ethyl methyl carbonate (99%, from Sigma- Aldrich). SEM images were taken of at least three places on each electrode, in which more than 100 particles were visible in each image. A particle fracture ratio w as calculated by counting the number of fractured particles divided by the total number of particles in the image. Only particlesmit-26171pctwith a minimum visible dimension of 10 pm were counted to prevent overcounting particle fragments and unclear particles. The analysis was done by hand in a single-blind manner, in which the researcher was unaware of the battery' and potential to which the electrode in each image had been subjected. The particle fracture ratio was averaged across the images and batteries cycled to each potential (at least nine separate images with at least 1,000 total particles counted per potential). A particle fracture rate was determined by calculating the rate of change between the averaged particle fracture ratios at adjacent potentials by using the scan rate of the cyclic voltammogram.

[0125] Results:

[0126] Improved Reproducibility of Acoustic Emission Experiments through EMI Removal:

[0127] Initial acousto-voltammetry experiments on graphite and NMC half-cells led to cumulative acoustic emissions per cell that varied by orders of magnitude (FIG. 2). The deviation between experiments on different electrodes and different scan rates was significantly reduced by the addition of EMI chokes, faraday cages, and the count and duration filters (FIG. 3). A similar improvement in the reproducibility of cumulative and electrochemically resolved acoustic energy across several trials was observed as well.

[0128] Acousto-Voltammetry on Poly crystalline and Single Crystal NMC Half-Cells:

[0129] NMC811. NMC532, and NMC532 single crystal were all tested by acousto-voltammetry across a potential range wider than conventionally experienced during constant current cycling. The electrochemically resolved acoustic emissions across four consecutive cyclic voltammograms on the same NMC811 half-cell (FIG. 4) showed two histogram peaks of acoustic activity, with one during delithiation (4.0 - 4.3 V) of the NMC811 electrode and then another during lithiation (3.4 - 3.8 V).

[0130] Dividing the electrochemically resolved acoustic emission analysis by cycle (FIG.6), the delithiation acoustic emissions predominantly occurred during the first two cycles. Most of the emissions during the first cycle occurred directly prior to the current peak, which appears to correspond to an influx of Li ions after a combination of all three expected phase transitions (Hl — > M, M — > H2, and H2 — > H3). The emissions in the second cycle appeared to peak around the current peaks around the M — > H2 and H2 — > H3 phase transitions. In other NMC811 half-cells tested by acousto-voltammetry, the distributions of delithiation acoustic emissions were very similar, with the two highest concentrations of acoustic activity occurring at 4.1 V (dominated by first-cycle acoustic emissions) and 4.15 V (generally between the M —> H2 and H2 —> H3 phase transitions). Conversely, fewer lithiation acoustic emissions occurred during the first cycle but appeared in similar numbers and magnitudes during every cycle afterward. A majority of the lithiation acoustic emissions occurred in the potential range during and directly after the M — Hl transition.mit-26171pct

[0131] Increasing the scan rate of the cyclic voltammetry' onNMC811 half-cells caused a greater peak separation in the current waves, indicating that the NMC811 phase transitions were delayed (delithiation phase transitions occurred at a higher potential and lithiation phase transitions occurred at a lower potential). Remarkably, the peaks in acoustic activity shifted to follow the current peaks associated with the deintercalation H2 — > H3 and lithiation M — > Hl transition (FIGS. 10-12).

[0132] A destructive assessment of NMC811 half-cells cycled to different potentials along the first cyclic voltammogram was conducted to assess the micro-structural effects throughout the potential range. The SEM imaging-based particle fracture ratio (FIG. 13) and particle fracture rate (FIG. 14) were calculated at each potential. The particle fracture ratio and rate increased near the deintercalation H2 —> H3 phase transition and decreased near the lithiation M — Hl phase transition (the absolute value of the particle fracture rate is shown in FIG. 14).

[0133] Electrochemically resolved acoustic-emission analysis on half-cells of polycrystalline NMC532 revealed a slightly different pattern. The lithiation acoustic emissions peaked across a similar potential range to the NMC811 half-cells (3.4 - 3.8 V) and correlated with the M — > Hl phase transition. However, the delithiation acoustic emissions peaked at a lower potential range (3.8 - 4.1 V), which was correlated with the Hl— > M phase transition (FIG. 18). NMC532 single cry stal (NMC532-SC) half-cells were tested across the same potential range as well, and the electrochemically resolved acoustic-emission analysis displayed a similarly shaped distribution of acoustic emissions relative to the phase transformation potentials, as in the NMC532 half-cells (FIG. 19); however, there were significantly fewer acoustic emissions and acoustic-emission cumulative energy than in the poly-crystalline samples (< 25% of that of poly-crystalline NMC532 half-cells). SEM imaging of NMC532 and NMC532-SC electrodes at high potential (4.6 V) revealed some degree of particle fracture in the NMC532 electrodes, but virtually no particle fracture in the NMC532-SC electrodes.

[0134] Electrochemically Resolved Acoustic-Emission Analysis on Graphite Half-Cells:

[0135] Graphite half-cells were tested by acousto-voltammetry to investigate the acoustic emissions during solid electrolyte interphase (SEI) formation. The electrochemically resolved acoustic emissions across three consecutive cyclic voltammograms on the same graphite half-cell (FIG. 24) showed three peaks of acoustic activity': one during discharging of the graphite electrode (positive current due to charging of the half-cell) between 0.2 - 0.5 V and two during charging of the graphite electrode, with one in the lithiation potential range (0.01 - 0.25 V) and the other at a higher potential (0.4 - 0.8 V). Each of the acoustic-emission peaks appeared to overlap with current peaks in the cyclic voltammograms. The acousticemission peak during graphite discharge overlapped with the delithiation current peak of the cyclic voltammogram, the low' potential acoustic-emission peak during graphite chargingmit-26171pctoverlapped with the lithiation-current peak, and the high potential acoustic-emission peak during graphite charging overlapped with the irreversible current peak that occurred during the first cyclic voltammogram. The latter can be viewed clearly when separating the electrochemically resolved acoustic-emission analysis individually by cycle. FIG. 25 directly shows the overlap between the acoustic emissions and the current peak generally associated with SEI formation. FIGS. 26 and 27 show the second and third cycle cyclic voltammograms without the clear SEI current peak and the corresponding acoustic emissions. The later cycles continued to have acoustic emissions during the lithiation and delithiation current peaks, but the number of acoustic emissions was significantly reduced in comparison to the first cycle.

[0136] An SEM image of a pristine graphite electrode is provided in FIG. 28. and an SEM image of a pristine single graphite particle is provided in FIG. 29. Online electrochemical mass spectrometry data of gas evolution rate during graphite formation by cyclic voltammetry is plotted in FIG. 30.

[0137] Battery-Acoustic Emissions Testing System Validation:

[0138] In order to verify that the acoustic emissions detected during the acoustovoltammetry experiments represented processes occurring in the graphite or NMC electrodes, other sources within the coin cell that could lead to additional acoustic hits and attenuation of the acoustic signal were investigated.

[0139] Within the half-cell construction, the most likely source of acoustic emissions outside of the cathode would be at the Li anode, which undergoes Li plating and stripping and SEI formation and cracking during the cyclic voltammogram. Previous studies have claimed that acoustic emissions of the Li anode can be neglected in half-cell experiments. To verify this claim, acoustic emission testing of Li symmetric cells was conducted using cyclic voltammetry over an extensive range of ±250 mV, resulting in a maximum current density of approximately 2.5 mAh / cm2Virtually no acoustic emissions were detected when the Li electrode was subject to a voltage less than a magnitude of 75 mV or a current density less than 0.9 mAh / cm2; however, approximately 3-4 acoustic emissions were detected per cyclic voltammogram above these two limits.

[0140] To analyze the effects of attenuation through the separator and electrolyte, an inverted Li || NMC811 half-cell was built by switching the locations of the electrodes during coin cell construction. The acoustic sensor remained in contact with the larger coin-cell cap, and thus in closer contact with the Li-metal electrode. Testing with the same electrochemical protocol as the conventional Li || NMC811 half-cells, a similar distribution of electrochemically resolved acoustic emissions, though with a fewer total number of emissions and lower acoustic energy' than in the conventionally built cells, was witnessed.mit-26171pct

[0141] Distinguishability of Batery Acoustic Emissions through WT and Unsupervised Clustering:

[0142] In separate experiments, acoustic emissions from graphite, NMC, and Li metal electrodes were identified and isolated from conventional EMI noise through careful experimental control and validation through destructive assessment. Unsupervised clustering based on transformations of the pre-distinguished transient waveforms was explored.

[0143] Wavelet transforms (WTs) were taken of acoustic emissions from several acoustovoltammetry experiments across different electrode materials in addition to WTs of acoustic emissions caused by EMI. acoustic emissions caused by physically tapping the bench near the experimental configuration were added to the model as well and denoted as ‘Noise -Vibration’. WT scalogram heatmaps of representative single emissions from each of the five groups showed differences in time-resolved frequency content. These differences can be quantitatively analyzed using multidimensional scaling (MDS), an algorithm that atempts to preserve relative pairwise root-mean-square distances between the WT scalograms during dimensionality reduction. Initially, there were two distinct clusters of acoustic emissions: one consisting nearly solely of acoustic emissions in graphite half-cell experiments during SEI formation and another consisting of NMC811 acoustic emissions (most likely from particle fracture and recombination), graphite (de)lithiation acoustic emissions. Li acoustic emissions, and a localized group of EMI noise acoustic emissions. The acoustic emissions caused by vibrational noise acoustic emissions spanned a wide space around the two clusters (FIG. 31). After applying the duration and count acoustic emission filters, a significant reduction in the number of noise emissions (EMI and vibration) can be seen while maintaining the identity and separation between the original two clusters (FIG. 32).

[0144] Discussion:

[0145] The results in this work demonstrate the sensitivity and efficacy of electrochemically resolved acoustic-emissions analysis of Li-ion bateries via careful experimental design and data processing of reproducible, process-correlated, and distinguishable acoustic emissions.

[0146] The reproducibility of the cumulative number and energy of acoustic emissions across nearly identically constructed and cycled Li-ion cells was significantly improved with the addition of EMI chokes. While previous batery -acoustic-emission work took great care to prevent vibrational interference in the measurement by physically isolating the experiment, seting a higher voltage (dB) threshold for determining acoustic emissions, and performing extensive background noise testing, we believe EMI noise contributed significantly to the widely varying number and energy of acoustic emissions both across studies on the same material and within individual studies. EMI noise contribution was mentioned in a few previous batery-acoustic-emission studies, but atempts to remove it were limited to removing acoustic emissions with a short duration or low count. We demonstrate here thatmit-26171pctEMI noise emissions can take several forms and continue to be present with the low-count filter. Thus, we conclude that more careful equipment design through EMI chokes and additional data processing steps is advantageous.

[0147] A degree of variation in the number of emissions and cumulative acoustic energy in the data reported in this work still remains, but the variation is most likely attributable to natural structural differences between individual electrodes and cell components. This is further supported by the SEM imaging data. The uncertainty in the particle fracture ratio or rate at each potential is largely caused by the differences between distinct cells, rather than differences within the same electrode. We see that the minor differences in the particle fracture ratio or rate between cells cycled to the same potential are positively correlated with the minor differences in cumulative acoustic emissions and energy. This result in particular underscores the sensitivity and potential accuracy of the acoustic emissions measurement.

[0148] The use of cyclic voltammetry’ as the simultaneous electrochemical measurement during the acoustic emissions testing allowed for better time and potential resolution of the phase transformations that occur in NMC cathodes during lithiation and delithiation. This was of particular interest, as the H2 H3 phase transition during deintercalation has been linked to particle fracture due to its rapid volume contraction. The NMC811 experiments display the result most effectively, as the H2 — >• H3 phase transition represents the greatest c-axis rate of change across any reasonable lithiation state (FIG. 5). The NMC532 H2 H3 phase transition occurs at a significantly higher potential (> 4.5V), which was less explored in this study. The NMC532 electrodes (both poly-crystalline and single crystal) showed increased acoustic activity around the Hl — > M phase transition during delithiation. This could be explained by the rapid volume and c-axis expansion that occurs during the potential window. Unlike NMC811, NMC532 undergoes its greatest volume rate of change during the Hl —> M phase transition potential window (3.7 - 4.0 V for poly-crystalline samples), which near perfectly aligns with the witnessed acoustic activity. Single-crystal NMC samples are known to have a large peak-to-peak separation during cyclic voltammetry, which was witnessed in this study as well. The acoustic activity’ occurred at the same potential as the (de)lithiation current peaks in the NMC532-SC, indicating that the acoustic emissions continued to occur during specific phase transitions.

[0149] Overall, all three NMC materials displayed a large amount of acoustic activity during the first deintercalation cycle, but less emissions and energy on subsequent cycles. If these acoustic emissions are correlated with particle fracture, then the result is supported by literature, as NMC particle fracture is expected to predominantly occur during the first deintercalation, and less so during further cycles. This is in agreement yvith a batteryacoustic-emission study conducted on LiNiO2 (an end member of the NMC cathodes).

[0150] The acoustic activity around the intercalation M — > Hl phase transition was unexpected, as no significant morphological changes or side reactions are expected at thatmit-26171pctpotential. However, confirmed by the SEM imaging data in this work and high-resolution X-ray nano-computed tomography data in literature, a portion of the NMC fractures visually disappear or close at this potential, as indicated by lattice contraction as well. The number and energy of acoustic emissions in this potential range are fairly consistent across the four cyclic voltammetry cycles, leading to the hypothesis that the emissions are being caused by a physically pseudo-reversible process, such as friction between the crystal grains as the particle contracts.

[0151] In order to validate that the acoustic emissions being recorded were directly related to particle fracture, a crystallinity study using NMC532 as the base material was conducted. Single-crystal electrode materials are known to fracture less, as most particle fractures in poly crystalline materials occur along crystal -grain boundaries rather than within crystals. Other than a higher active surface area per mass of active material and slightly higher active material loading of the NMC532-SC electrodes, all other experimental variables were kept identical. The significant reduction of acoustic hits and energy in the NMC532-SC half-cells appears to indicate that the majority of the acoustic activity detected is due to particle fracture. The remaining acoustic activity from theNMC532-SC electrodes could be attributed to a smaller number of particle fractures or potentially side reactions on the Li anode.

[0152] The acoustic activity on graphite appeared to occur during lithium (de)intercalation and SEI formation. Similar to NMC cathodes, it appears that the acoustic emissions detected during (de)intercalation may result from particle fracture or exfoliation, which are known degradation mechanisms of graphite; however, further destructive experimental validation on the graphite electrode was not attempted in this study. The average acoustic energy from each of the acoustic emissions in the (de)intercalation potential ranges is quite low, indicating that the visual change to the material would most likely be minimal. The acoustic emissions during the SEI formation potential range have a greater average acoustic energy and generally have a longer duration and a lower frequency. The initial details of these emissions appear to identity’ them as gas emissions from previous acoustic-emission and battery-acoustic-emission literature.

[0153] Past battery -acoustic-emission studies have mentioned the possibility of detecting gas evolution from graphite and other Li-ion battery anodes, such as Si, but have struggled to definitively determine that gas evolution was responsible for certain acoustic emissions due to the overlap with particle fracture emissions. In this case, the potential range where the acoustic activity’ occurred in this study precisely overlaps with the ethylene gas (C2H4) evolution rate measured using graphite electrodes, a similar electrolyte, and cyclic voltammetry by online electrochemical mass spectrometry data in literature, corroborating gas evolution as the source of the acoustic emissions (FIG. 30). This result contrasts with the conclusion drawn from a battery-acoustic-emission study conducted on a carbon blackmit-26171pct(Super P®, 99+%, Alfa Aesar)and polymer binder electrode, in which chronoamperometry and cyclic voltammetry7were used simultaneously with acoustic-emission analysis [A.Schiele, et al., “Silicon Nanoparticles with a Polymer-Derived Carbon Shell for Improved Lithium-Ion Batteries: Investigation into Volume Expansion, Gas Evolution, and Particle Fracture.” 3 ACS Omega 16706-16713 (2018)]. Therein, the authors claimed that gas evolution had no noticeable effect on the acoustic activity; however, roughly a third of the acoustic emissions detected occurred during the first lithiation of the carbon and overlapped with a current peak around 0.4 - 0.8 V, indicative of SEI side reactions.

[0154] Investigating the acoustic activity on the Li anode revealed that the number and energy of acoustic emissions were directly related to the potential and current density. From literature and Li-symmetric cell testing in this work, the overpotential experienced by the Li-anode is positively correlated to current density. Almost no acoustic emissions were detected until a current density of 1 mAh / cm2was reached. It should be mentioned that the potential regions of greatest acoustic activity in the NMC half-cells occurred when the current density was in the range of 0.3 - 1.3 mAh / cm2. While a few acoustic emissions could be from the Li anode, there should be no more than 3-4 per cycle, given the acoustic activity in the Li-symmetric tests and the time spent in the high-current-density region.

[0155] Further confirmation that acoustic emissions from the Li anode are not significantly impacting the electrochemically resolved acoustic analysis comes from the inverted Li 11 NMC811 tests. The significantly lower number and lower energy of acoustic emissions during NMC 811 half-cell cyclic voltammetry indicate that strong attenuation of the battery emissions occurs when measuring emissions that cross through cell components, such as the separator and electrolyte. Lower energy emissions, such as those present during the M — > Hl phase transition in NMC811 lithiation, may not be registered at all after crossing through the cell under the chosen sensitivity settings in this study.

[0156] Signal processing through the wavelet transform (WT) enables the acquisition of high-resolution time and frequency data from an acoustic wave in a single scalogram. This form of analysis also enables comparisons with previous battery-acoustic-emission studies that predominantly looked at peak frequency or duration as key acoustic-emission features. Qualitative comparisons between the WTs of representative emissions from the five categories show that each group is visually distinct. EMI tends to be a wideband signal that stretches beyond 1 MHz with an extremely short duration. This is the mathematical result of a single or quick double-peak waveform. While many battery -acoustic-emission studies would have successfully eliminated many of these emissions by rejecting acoustic emissions with less than 2 counts, at least two other scalogram forms of EMI were discovered in our dataset. One is the presence of multiple EMI emissions in a single transient acoustic-emission dataset, which incorrectly gives the appearance of a multiple-count wave, and the other is a single-frequency, constant-amplitude, long-duration EMI emission, which has generally notmit-26171pctbeen accounted for in previous studies, though it was mentioned to be manually removed in a single battery-acoustic-emission study. Interestingly, vibrational noise can appear to have a similar scalogram to the latter EMI emission and additionally clusters together in the MDS unsupervised analysis.

[0157] Graphite acoustic emissions in the SEI formation potential range are generally low-frequency and long-duration but are distinct from vibrational noise and long duration EMI emissions through having anon-constant amplitude. Previous battery-acoustic-emission studies have believed this type of emission to be from gas evolution, and perhaps the most convincing data to support this hypothesis is from a paper that also took the WT of an acoustic emission hit caused by electrochemically induced gas evolution on a graphitic electrode. Our study appears to corroborate this for gas evolution caused by SEI formation in an operando Li-ion cell, especially because other mechanisms, such as lithium (de)intercalation and particle fracture, are not expected to occur significantly in the potential range, given the slow-rate cyclic voltammogram and the staging nature of lithium intercalation into graphite.

[0158] The NMC811 acoustic emissions have a wideband frequency response with a shorter duration. Because of these details, the NMC811 emissions tend to cluster near the traditional EMI noise emissions; however, a clear distinction lies in the duration and count values. NMC811 emissions are shorter than graphite gas evolution acoustic emissions, but distinctly longer than traditional EMI emissions. Previous battery-acoustic-emission literature has suggested that particle fracture emissions tend to have a peak frequency above 500 kHz, and this was seen in several WT scalograms of NMC811 acoustic emissions in this study. A short-duration acoustic emission hit is still seen; however, the peak frequency could vary within the wideband. Because these acoustic emissions still have a short duration and NMC811 tends to only evolve significant amounts of gas above 4.4 V, it does not appear that these emissions came from gas evolution. Further corroboration is once again found in the wavelet-transformed acoustic emission study, in which acoustic emissions from the induced fracture of a graphitic electrode appeared to have a wideband signal with a peak frequency around 160 kHz. The NMC811 result, in particular, highlights the utility of using the combination of acousto-voltammetry and the wavelet transform for acoustic emission hit classification.

[0159] Li acoustic emissions have similar time and frequency data to NMC811 hits, which could potentially be explained by the continual fracture of the SEI layer during cycling. However, the distinction between the two lies in the amplitude of the acoustic emissions, in which the Li emissions are significantly lower in energy'. FIG. 31 shows the Li acoustic emissions clustered with the NMC811 acoustic emissions, as all emissions were normalized prior to the analysis, but most of the Li acoustic emissions can be isolated or removed with an energy' filter, if desired.mit-26171pct

[0160] Interestingly, there are a few NMC811 and Li acoustic emissions that are close to the graphite-SEI cluster; however, over 95% of the NMC811 acoustic emissions in this cluster occur at a potential greater than 4.4 V (across several acousto-voltammetry experiments), which could feasibly indicate gas evolution from the cathode material. Similarly, the graphite (de)intercalation acoustic emissions in the NMC811 / Li cluster show that 90% of them occur during delithiation or below a potential of 0.3 V during lithiation. These acoustic emissions may be due to graphite-particle fracture or delamination.

[0161] After applying the count and duration filters, we more effectively resolve the two clusters of acoustic emissions on the 2-dimensional scaling plot, which potentially could represent specific mechanisms, namely, gas generation emissions and particle fracture emissions (FIG. 32). It is important to note that some EMI and vibrational noise acoustic emissions still persist, despite the filters. Particularly concerning are those caused by EML as they overlap with some NMC811 and Li acoustic emissions, indicating that certain particle fracture-type emissions have a similar time and frequency content to EMI emissions. The WT-MDS method can be utilized to remove any seemingly electrode-based acoustic emissions that are close to the EMI noise acoustic emission group in the multidimensional scaling (MDS) plot. This process would potentially remove some real electrode-based acoustic emissions but would increase confidence in eliminating the effects of EMI in the experiment. Ultimately, this result underscores the notion that more complex methods of waveform analysis beyond simple filters are needed to more completely isolate EMI noise from battery-acoustic-emission experiments.

[0162] Conclusions:

[0163] The methodology for performing electrochemically resolved acoustic-emissions analysis using acousto-voltammetry was demonstrated on Li-ion half-cells to evaluate SEI formation on graphite and particle fracture in NMC811 in operando. After careful elimination of acoustic noise due to EMI and battery-acoustic-emission system validation. Acoustic emissions were reproducibly detected when measured simultaneously with cyclic voltammetry. Through comparisons with previous gas evolution experiments and ex-situ SEM analysis, correlations were corroborated between acoustic emissions and specific battery mechanisms, namely SEI formation and particle fracture on graphite and NMC811 electrodes, respectively. Finally, signal processing using the WT enabled distinguishability between acoustic emissions measured from different proposed mechanisms and demonstrated that EMI and vibrational noise require more complex methods than count and duration filters to isolate. These results illustrate the capability of operando acoustic-emission analysis as a sensitive and accessible NDE method for Li-ion batteries and potentially other electrochemical systems, when performed in an electrochemically resolved and well-characterized mannermit-26171pct

[0164] It should be understood that the subject matter defined in the appended claims is not necessarily limited to the specific implementations described above. The specific implementations described above are disclosed as examples only.

[0165] In describing embodiments, herein, specific terminology is used for the sake of clarity. For the purpose of description, specific terms are intended to at least include technical and functional equivalents that operate in a similar manner to accomplish a similar result. Additionally, in some instances where a particular embodiment includes a plurality of system elements or method steps, those elements or steps may be replaced with a single element or step. Likewise, a single element or step may be replaced with a plurality of elements or steps that serve the same purpose. Further, where parameters for various properties or other values are specified herein for embodiments, those parameters or values can be adjusted up or down by 1 / 100th, 1 / 50th. l / 20th, l / 10th, l / 5th, l / 3rd, 1 / 2, 2 / 3ld, 3 / 4th, 4 / 5th, 9 / 10th, 19 / 20th, 49 / 50th, 997100th, etc. (or up by a factor of 1, 2, 3, 4, 5, 6, 8, 10, 20, 50, 100, etc.), or by rounded-off approximations thereof or within a range of the specified parameter up to or dow n to any of the variations specified above (e.g, for a specified parameter of 100 and a variation of 1 / 100th, the value of the parameter may be in a range from 0.99 to 1.01), unless otherwise specified. Further still, where methods are recited and where steps / stages are recited in a particular order — with or without sequenced prefacing characters added for ease of reference — the steps / stages are not to be interpreted as being temporally limited to the order in which they are recited unless otherwise specified or implied by the terms and phrasing. |00166| Additional examples consistent with the present teachings are set out in the following numbered clauses:1. An electrochemical system including an apparatus configured to analyze an internal state of the system, the electrochemical system comprising:an anode;a cathode;an electrolyte with which the anode and the cathode are in contact;a casing in which the electrolyte, the anode, and the cathode are contained; sensors positioned and configured to simultaneously record acoustic emissions generated in the electrochemical system and electrochemical data inside the casing; and a signal-processing system configured to correlate the acoustic emission and electrochemical data to gain useful information about the internal state of the electrochemical system.2. The electrochemical system of clause 1, wherein the electrochemical data that at least one of the sensors is configured to record includes at least one of the following: electric current, electric charge, or voltage.mit-26171pct3. The electrochemical system of clause 1 or 2, further comprising a processor in communication with the sensors, wherein the processor and the sensors are configured to record and analyze transient acoustic emission-signal data.4. The electrochemical system of clause 3, wherein the transient acoustic emission-signal data includes at least one of the following: acoustic-signal amplitude, acoustic-signal duration, acoustic-signal energy, acoustic-signal waveform, or acoustic-signal frequency. 5. The electrochemical system of clause 3 or 4, further comprising a processor in communication with the sensors, wherein the processor is configured to process acoustic emission transient signals and extract frequency and time information to gain more detailed information about the electrochemical system.6. The electrochemical system of any of clauses 1-5. wherein the electrochemical data is data produced by cyclic voltammetry or linear sweep voltammetry.7. The electrochemical system of any of clauses 1-5. wherein the electrochemical data is data produced by electrochemical impedance spectroscopy.8. The electrochemical system of any of clauses 1-5, wherein the electrochemical data is data produced by potentiostatic or galvanostatic intermittent titration.9. The electrochemical system of any of clauses 1-8, wherein the useful information about the internal state of the electrochemical system comprises at least one of the following: state of health, remaining useful life, or state of safety of the electrochemical system.10. The electrochemical system of any of clauses 1-9, wherein the useful information about the internal state of the electrochemical system comprises electrochemically resolved acoustic emissions to identify specific mechanisms within the electrochemical system.1 1. The electrochemical system of any of clauses 1-10, wherein the useful information about the internal state of the electrochemical system comprises at least one of the following: solid fracture, interfacial corrosion, frictional sliding, bubble (gas) formation, or other physical processes associated with material changes or degradation of the electrochemical system. 12. The electrochemical system of clauses 1-11. wherein the electrochemical system is a battery.13. The electrochemical system of clause 12, wherein the battery is selected from a lithium-ion battery, a solid-state battery, or a flow battery.14. The electrochemical system of any of clauses 1-11, wherein the electrochemical system is a fuel cell.15. The electrochemical system of clause 14, wherein the fuel cell is a proton-exchange membrane fuel cell or a solid-oxide fuel cell.16. The electrochemical system of any of clauses 1-11, wherein the electrochemical system is an electrolyzer.17. The electrochemical system of clause 16, wherein the electrolyzer produces at least one of the following: hydrogen, nitrogen, oxygen, carbon monoxide, fuel (such as amit-26171pcthydrocarbon), or chemicals (such as ethanol, ethylene, and formic acid), or consumes at least one of the following: water, carbon dioxide, or ammonia.18. The electrochemical system of any of clauses 1-17, wherein the sensors comprise a piezoelectric acoustic sensor for acoustic emission detection.19. The electrochemical system of any of clauses 1-18, wherein the acoustic emissions comprise spatially varied acoustic emissions.20. The electrochemical system of any of clauses 1-19, further comprising electromagnetic interference chokes and shielding configured to achieve at least one of the following effects: eliminating spurious acoustic emission signals or improving signal detection.21. The electrochemical system of any of clauses 1-20, further comprising the following components:Faraday cages; andat least one of the following: ferrite beads or toroids,wherein these components are configured to improve spurious signal removal and true signal detection.22. The electrochemical system of any of clauses 1-21, wherein the sensors comprise at least one of:a system for recording current-voltage data;a sensor for recording temperature;a sensor for detecting defects in the electrochemical system; ora sensor for detecting contamination or degradation in the cathode, anode, or electrolyte.23. The electrochemical system of any of clauses 1-22, wherein at least one of the anode and the cathode comprises at least one electrode active material selected from: graphite, metal oxides, metal phosphates, silicon, or silicon dioxide.24. The electrochemical system of any of clauses 1-23, wherein the signal processing system is further configured to measure at least one of the following: state of health of the electrochemical system, remaining useful life of the electrochemical system, or state of safety of the electrochemical system based on at least one of the following: number of detected acoustic emissions or cumulative amount of acoustic energy detected via the detection of the acoustic emissions.25. A method of analyzing an electrochemical system, comprising an anode, a cathode, and an electrolyte, the method comprising:simultaneously recording:acoustic emissions; andelectrochemical data; andmit-26171pctidentifying correlations between acoustic emission and the electrochemical data to infer internal processes or mechanisms to gain information about the electrochemical system.26. The method of clause 25, wherein the recorded electrochemical data includes at least one of the following: electric current, electric charge, or voltage.27. The method of clause 25 or 26, wherein transient acoustic emission signals are recorded and analyzed.28. The method of clause 27, wherein the transient acoustic emission signals include at least one of the following: amplitude, duration, energy, waveform, or frequency.29. The method of clause 28, wherein acoustic emission transient signals are processed to extract frequency and time information in order to gain more detailed information about the electrochemical system.30. The method of any of clauses 25-29. wherein the electrochemical data is produced by cyclic voltammetry or linear sweep voltammetry.31. The method of any of clauses 25-29. wherein the electrochemical data is produced by electrochemical impedance spectroscopy.32. The method of any of clauses 25-29, wherein the electrochemical data is produced by potentiostatic or galvanostatic intermittent titration.33. The method of any of clauses 25-32, wherein the information about the electrochemical system comprises a state of health of the electrochemical system, remaining useful life of the electrochemical system, and / or state of safety of the electrochemical system.34. The method of any of clauses 25-33, wherein correlations of the data are identified to infer internal processes or mechanisms, comprising electrochemically resolving the acoustic emissions to identify specific mechanisms within the electrochemical system.35. The method of clause 34, wherein the internal processes or mechanisms are selected from solid fracture, interfacial corrosion, frictional sliding, bubble (gas) formation, or other physical processes associated with material changes or degradation of the electrochemical system.36. The method of any of clauses 25-35. wherein the electrochemical system is a battery. 37. The method of clause 36, wherein the battery is a lithium-ion battery, a solid-state battery, or a flow battery.38. The method of any of clauses 25-35, wherein the electrochemical system is a fuel cell.39. The method of clause 38, wherein the fuel cell is a proton-exchange membrane fuel cell or a solid-oxide fuel cell.40. The method of any of clauses 25-35, wherein the electrochemical system is an electrolyzer.41. The method of clause 40, wherein the electrolyzer is producing at least one of the following: hydrogen, nitrogen, oxygen, carbon monoxide, fuel (such as a hydrocarbon), ormit-26171pctchemicals (such as ethanol, ethylene, and formic acid), or consuming at least one of the following: water, carbon dioxide, or ammonia.42. The method of any of clauses 25-41, wherein the acoustic-emission recording is obtained using a piezoelectric acoustic sensor.43. The method of any of clauses 25-42, wherein the acoustic emissions comprise spatially varied acoustic emissions.44. The method of clause 25-37, 42, or 43, where the method is practiced in a battery cell manufacturing facility.45. The method of clause 25 using the electrochemical system of any of clauses 1-24.

[0167] While this invention has been shown and described with references to particular embodiments thereof, those skilled in the art will understand that various substitutions and alterations in form and details may be made therein without departing from the scope of the invention. Further still, other aspects, functions, and advantages are also within the scope of the invention; and all embodiments of the invention need not necessarily achieve all of the advantages or possess all of the characteristics described above. Additionally, steps, elements, and features discussed herein in connection with one embodiment can likewise be used in conjunction with other embodiments. The contents of references, including reference texts, journal articles, patents, patent applications, etc., cited throughout the text are hereby incorporated by reference in their entirety for all purposes; and all appropriate combinations of embodiments, features, characterizations, and methods from these references and the present disclosure may be included in embodiments of this invention. Still further, the components and steps identified in the Background section are integral to this disclosure and can be used in conjunction with or substituted for components and steps described elsewhere in the disclosure within the scope of the invention.

Claims

mit-26171pctCLAIMSWhat is claimed is:

1. An electrochemical system including an apparatus configured to analyze an internal state of the system, the electrochemical system comprising:an anode;a cathode;an electrolyte with which the anode and the cathode are in contact;a casing in which the electrolyte, the anode, and the cathode are contained; sensors positioned and configured to simultaneously record acoustic emissions generated in the electrochemical system and electrochemical data inside the casing; and a signal-processing system configured to correlate the acoustic emission and electrochemical data to gain useful information about the internal state of the electrochemical system.

2. The electrochemical system of claim 1, wherein the electrochemical data that at least one of the sensors is configured to record includes at least one of the following: electric current, electric charge, or voltage.

3. The electrochemical system of claim 1, further comprising a processor in communication with the sensors, wherein the processor and the sensors are configured to record and analyze transient acoustic emission-signal data.

4. The electrochemical system of claim 3, wherein the transient acoustic emission-signal data includes at least one of the following: acoustic-signal amplitude, acoustic-signal duration, acoustic-signal energy, acoustic-signal waveform, or acoustic-signal frequency.

5. The electrochemical system of claim 3, further comprising a processor in communication with the sensors, wherein the processor is configured to process acoustic emission transient signals and extract frequency and time information to gain more detailed information about the electrochemical system.

6. The electrochemical system of claim 1, wherein the electrochemical data is data produced by cyclic voltammetry or linear sweep voltammetry.

7. The electrochemical system of claim 1, wherein the electrochemical data is data produced by electrochemical impedance spectroscopy.mit-26171pct8. The electrochemical system of claim 1, wherein the electrochemical data is data produced by potentiostatic or galvanostatic intermittent titration.

9. The electrochemical system of claim 1, wherein the useful information about the internal state of the electrochemical system comprises at least one of the following: state of health, remaining useful life, or state of safety of the electrochemical system.

10. The electrochemical system of claim 1, wherein the useful information about the internal state of the electrochemical system comprises electrochemically resolved acoustic emissions to identify specific mechanisms within the electrochemical system.

11. The electrochemical system of claim 10. wherein the useful information about the internal state of the electrochemical system comprises at least one of the following: solid fracture, interfacial corrosion, frictional sliding, bubble (gas) formation, or other physical processes associated with material changes or degradation of the electrochemical system.

12. The electrochemical system of claim 1, wherein the electrochemical system is a battery’.

13. The electrochemical system of claim 12, wherein the battery is selected from a lithium- ion battery, a solid-state battery, or a flow battery.

14. The electrochemical system of claim 1, wherein the electrochemical system is a fuel cell.

15. The electrochemical system of claim 14. wherein the fuel cell is a proton-exchange membrane fuel cell or a solid-oxide fuel cell.

16. The electrochemical system of claim 1, wherein the electrochemical system is an electrolyzer.

17. The electrochemical system of claim 16, wherein the electrolyzer produces at least one of the following: hydrogen, nitrogen, oxygen, carbon monoxide, fuel, or a chemical selected from ethanol, ethylene, or formic acid, or consumes at least one of the following: water, carbon dioxide, or ammonia.

18. The electrochemical system of claim 1, wherein the sensors comprise a piezoelectric acoustic sensor for acoustic emission detection.mit-26171pct19. The electrochemical system of claim 1, wherein the acoustic emissions comprise spatially varied acoustic emissions.

20. The electrochemical system of claim 1, further comprising electromagnetic interference chokes and shielding configured to achieve at least one of the following effects: eliminating spurious acoustic emission signals or improving signal detection.

21. The electrochemical system of claim 1, further comprising the following components:Faraday cages; andat least one of the following: ferrite beads or toroids,wherein these components are configured to improve spurious signal removal and true signal detection.

22. The electrochemical system of claim 1, wherein the sensors comprise at least one of:a system for recording current-voltage data;a sensor for recording temperature;a sensor for detecting defects in the electrochemical system; ora sensor for detecting contamination or degradation in the cathode, anode, or electrolyte.

23. The electrochemical system of claim 1, wherein at least one of the anode and the cathode comprises at least one electrode active material selected from: graphite, metal oxides, metal phosphates, silicon, or silicon dioxide.

24. The electrochemical system of claim 1, wherein the signal processing system is further configured to measure at least one of the following: state of health of the electrochemical system, remaining useful life of the electrochemical system, or state of safety of the electrochemical system based on at least one of the following: number of detected acoustic emissions or cumulative amount of acoustic energy detected via the detection of the acoustic emissions.

25. A method of analyzing an electrochemical system, comprising an anode, a cathode, and an electroly te, the method comprising:simultaneously recording:acoustic emissions; andelectrochemical data; andmit-26171pctidentifying correlations between acoustic emission and the electrochemical data to infer internal processes or mechanisms to gain information about the electrochemical system.

26. The method of claim 25, wherein the recorded electrochemical data includes at least one of the following: electric current, electric charge, or voltage.

27. The method of claim 25, wherein transient acoustic emission signals are recorded and analyzed.

28. The method of claim 27. wherein the transient acoustic emission signals include at least one of the following: amplitude, duration, energy, waveform, or frequency.

29. The method of claim 28, wherein acoustic emission transient signals are processed to extract frequency and time information in order to gain more detailed information about the electrochemical system.

30. The method of claim 25, wherein the electrochemical data is produced by cyclic voltammetry or linear sweep voltammetry.

31. The method of claim 25, wherein the electrochemical data is produced by electrochemical impedance spectroscopy.

32. The method of claim 25, wherein the electrochemical data is produced by potentiostatic or galvanostatic intermittent titration.

33. The method of claim 25. wherein the information about the electrochemical system comprises a state of health, remaining useful life, and / or state of safety of the electrochemical system.

34. The method of claim 25, wherein correlations of the data are identified to infer internal processes or mechanisms, comprising electrochemically resolving the acoustic emissions to identify specific mechanisms within the electrochemical system.

35. The method of claim 34, wherein the internal processes or mechanisms are selected from solid fracture, interfacial corrosion, frictional sliding, bubble (gas) formation, or other physical processes associated with material changes or degradation of the electrochemical system.mit-26171pct36. The method of claim 25, wherein the electrochemical system is a battery7.

37. The method of claim 36, wherein the battery7is a lithium-ion battery7, a solid-state battery, or a flow battery7.

38. The method of claim 25, wherein the electrochemical system is a fuel cell.

39. The method of claim 38, wherein the fuel cell is a proton-exchange membrane fuel cell or a solid-oxide fuel cell.

40. The method of claim 25. wherein the electrochemical system is an electrolyzer.

41. The method of claim 40, wherein the electrolyzer is producing at least one of the following: hydrogen, nitrogen, oxygen, carbon monoxide, fuel, or a chemical selected from ethanol, ethylene, or formic acid, or consuming at least one of the following: water, carbon dioxide, or ammonia.

42. The method of claim 25, wherein the acoustic-emission recording is obtained using a piezoelectric acoustic sensor.

43. The method of claim 25, wherein the acoustic emissions comprise spatially7varied acoustic emissions.

44. The method of claim 25, where the method is practiced in a battery cell manufacturing facility.

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