Circuit parameters extraction algorithm for a lithium-ion battery charging system incorporated with electrochemical impedance spectroscopy

Electrochemical impedance spectroscopy (EIS) is a powerful tool for the non-destructive diagnosis of lithium ion batteries (LIBs). Thanks to the measurement over a wide frequency range, electrochemical processes of different kinetics are reflected in EIS, which contains rich information on battery aging and degradation.Distribution of relaxation times (DRT) method has been increasingly utilised to interpret EIS data. Compared to conventional EIS presentations such as Nyquist plot and Bode plot, DRT isolates the processes with different time constants and gives an explicit showcase of timescales in the battery [1]. Another advantage of DRT is the possibility to separate contributions from cathode and anode without the meticulous work to make three-electrode cells, given that relaxation time peaks can be identified with half cells [2]. The information acquired through DRT can provide insight into battery degradation paths and help improve data-driven methods for battery diagnosis/prediction.This work looks into the DRT evolution of commercial NMC/graphite cylindrical cells (Sony US14500VR2 with a nominal capacity of 715mAh) under various cycling conditions. Before the experiment starts, the cells are in shipping status i.e. undergone pre-aging and kept at approximately 70% state of charge (SoC). All cells then go through one 0.1C/0.1C cycle and 99 continuous cycles under various C-rates and temperatures (see table 1). The lower C-rates under 25ºC and 35ºC are scaled against 45ºC by Arrhenius relation. All charges are constant-current constant-voltage and all discharges are constant-current, between 3V and 4.2V. Impedance spectra are measured over 10kHz~0.1Hz range after being fully charged and fully discharged in each cycle.The impedance spectra measured after every full charge of cells 1~5 are shown in Figure 1(a) ~ (e). The decrease of semicircle size as temperature increases can be seen. During continuous cycling, internal resistance and semicircle size grow monotonically as cycle number increases. While the semicircles in each EIS curve are overlapping, the impedance components with different relaxation times are clearly separated in the DRT plotted in Figure 2. In Figure 2(a) and (b), there are constantly four relaxation time peaks as cycle number increases in 25ºC. The feature time constant in lies tightly within 25ms~50ms range, corresponding to 20Hz~40Hz frequencies, regardless of C-rates. In Figure 2(c) and (d), relaxation time peaks differ with C-rates right after 35ºC cycling starts. With 0.5C/1C rate, the evolution trend of relaxation time is similar to 25ºC cases. With 1C/2C rate however, there are initially only three relaxation time peaks and the mid-frequency (between 0.1s and 1s) peak “splits” into two as cycle number approaches 100. This could be related to joule heating resulting from higher C-rate or kinetic factors, and is more similar to the 45ºC case as shown in Figure 2(e). In 45ºC with 1C/2C rate, the relaxation time peaks start with three and “split” into four around the 60th cycle.While the evolution of DRT needs further interpretation and more long-term experiments, we can see the effective of time scale separation for EIS under various cycling conditions. The time scale features can be incorporated into data-driven methods e.g. machine learning to aim at accurate battery diagnosis/prediction. Also, the fact that feature relaxation times (may be battery-type specific) are distributed in a relatively narrow range suggests the EIS measurement can be done with reduced frequency points to save on-board resources for future system-level application.This work is supported by Faraday Institution (EP/S003053/1) and North-East Centre of Energy Materials (EP/R021503/1) funded by EPSRC.[1] Ciucci, F., & Chen, C. (2015). Analysis of electrochemical impedance spectroscopy data using the distribution of relaxation times: A Bayesian and hierarchical Bayesian approach. Electrochimica Acta, 167, 439-454.[2] Sabet, P. S., Stahl, G., & Sauer, D. U. (2018). Non-invasive investigation of predominant processes in the impedance spectra of high energy lithium-ion batteries with Nickel-Cobalt-Aluminum cathodes. Journal of Power Sources, 406, 185-193. Figure 1

Under irradiation the post-transition corrosion rates of Zircaloy are enhanced relative to out-of-flux rates. In an effort to better understand the effects of different mixed-field radiation environments and the variables that may contribute to this enhancement a series of in situ electrochemical impedance spectroscopy (EIS) tests were conducted in the Halden Test Reactor under PWR type conditions. The EIS tests were conducted using five identically fabricated electrode cells, which employed Zircaloy-4 tipped working electrodes. Approximately 30 μm thick oxides were prefilmed on the electrode tips prior to test insertion. The electrode test train was designed in a manner that enabled a wide range of gamma and neutron radiation flux conditions to be evaluated. Gamma fluxes (E ≥1 MeV) ranged from 1.7×1013 to 1.3×1014 cm−2 s−1 while the fast neutron fluxes (E ≥1 MeV) ranged from 2.9×1010 to 3.2×1013 cm−2 s−1. In addition, the EIS tests were conducted over temperatures ranging from 250 to 335°C. Electrode sets were situated into two basic radiation environments, which were differentiated by the magnitude and relative proportion of the mixed radiation field. In one environment, where the fast neutron flux was low, the relative gamma radiation component was high (i.e., high gamma-to-neutron ratio environment). In the other environment, where the fast neutron flux was high, the relative gamma radiation component was low (i.e., low gamma-to-neutron ratio environment). Based on the low frequency limits, the impedance moduli and inferred corrosion rates were found to be a complex function of temperature, and the relative proportion of gamma and neutron radiation. At low temperatures of 250°C it was found that the electrode sets which were exposed under high gamma-to-neutron ratios exhibited low frequency impedances that were almost 2.5 times lower than the case for the electrode sets which were placed in low gamma-to-neutron ratio. This occurred even though the absolute magnitude of the gamma and neutron flux fields decreased. This would imply that the corrosion rate is higher under high gamma-to-neutron ratios than under low gamma-to-neutron ratios. Conversely, at high temperatures, 335°C, only very small differences in impedance were noted as a function of radiation environment. Post-test destructive examination of the Zircaloy tipped electrodes indicates that the growth of the oxide formed during the in-pile phase of testing is consistent with the in situ EIS measurements obtained in-pile. The porous nature of the post-transition oxide coupled with the apparent correlation with gamma radiation suggests that heterogeneous radiolysis within the corrosion product film plays an important role in enhancing post-transition corrosion kinetics.

Electrochemical impedance spectroscopy (EIS) is a powerful nondestructive tool that is widely used to identify physical parameters and health diagnostics in lithium-ion batteries.1 By applying a small perturbation of either current or voltage and subsequently analyzing the electrochemical responses over a range of frequencies, information can be revealed about the charge-transfer kinetics, transport phenomena, and thermodynamics of the cell.2 Small amplitude perturbations are used to ensure the battery operates in its linear-response regime. The frequency-dependent cell impedance Z(ω) is most commonly analyzed by fitting an equivalent circuit model and extracting parameters from these fits. However, equivalent circuit models limit the amount of physically insightful information that can be extracted from battery EIS data.3,4 Moreover, operating in the linear response regime also imposes a fundamental limitation on the total quantity of information contained in an impedance spectrum, since many of the physicochemical processes in a battery are inherently nonlinear in character. Nonlinear electrochemical impedance spectroscopy (NLEIS) is an adjunct to EIS where larger amplitude sinusoidal current or potential perturbations are applied, and the nonlinear response of the battery is measured by the presence of higher harmonics in the output. Through a fairly straightforward analysis, a purely frequency-dependent second harmonic “impedance” Z2(ω) can be defined. Higher harmonic, or nonlinear, electrochemical impedance spectra can provide deep insights into processes occurring in the electrochemical device under test, including insights into physicochemical processes that are invisible to standard (linearized) EIS approach.5 Here, Samsung 18650 LiNMC | C batteries (capacity = 1500 mAh) were cycled under various rates and conditions, with NLEIS data acquired throughout the duration of its cycle time, for different states of charge. For this particular battery capacity and chemistry, a typical “moderate” current perturbation was 300 to 500 mA. The experimentally measured nonlinear electrochemical impedance spectrum Z2(ω) can be compared to results derived from the psuedo-2D model of a Li-ion battery6. Our physics-based approach for computing the nonlinear electrochemical impedance is a natural extension of the linearized EIS analysis that has been done previously.4 We show that NLEIS experiments have all the information of EIS, plus additional information on the electrode thermodynamics (low frequencies) and charge transfer kinetics. We show that aggressive cycling increases the kinetic impedance of the positive electrode, with little impact on the negative electrode. NLEIS shows a correlated effect, but it is possible to use Z2(ω) to discern more about the nature of the interfacial degradation occurring on the positive electrode. In short, using nonlinear impedance in coordination with the linear impedance can provide further insight into more sensitive physicochemical phenomena that can be used to diagnose the state of health of Li-ion batteries during aging. [1] N. Lohmann, P. Weßkamp, P. Haußmann, J. Melbert, and T. Musch, J. Power Sources, 273, 613-623 (2015) [2] C. Chen and P.P. Mukherjee, Phys. Chem. Chem. Phys., 17, 9812-9827 (2015) [3] T. Osaka, D. Mukoyama, and H. Nara, J. Electrochem. Soc. 162, 2529-2537 (2015) [4] M. Doyle, J. P. Meyers, and J. Newman, J. Electrochem. Soc. 147, 99-110 (2000) [5] J.R. Wilson, D. T. Schwartz, and S. B. Adler, Electrochimica Acta, 51, 1389-1402 (2006) [6] T.F. Fuller, M. Doyle, and J. Newman, J. Electrochem. Soc. 141, 1-10 (1994)

Zirconium and its alloys are widely used in chemical industries due to the high resistance to corrosion and H2 embrittlement in many aggressive media [1,2]. These properties are exhibited by the metal due to the formation of stable, protective passive film of ZrO2 [3]. Although Zr metal exhibits excellent corrosion resistance in most of the harsh environments, it readily dissolves in acidic fluoride media [4]. Zr dissolution mechanism in acidic fluoride medium was studied using the reaction mechanism analysis of potentiodynamic polarization data in various HF solutions [5]. A four step mechanism with two adsorbed intermediates predicts the major characteristics of the polarization curves. It was shown that the remaining HF and HF2 - are the key species involved in the dissolution of Zr in acidic fluoride medium. The confidence in the reaction mechanism identification will be more if the model can predict the impedance spectra observed at different dc potentials in different concentrations of HF. Compared to the polarization data, which is obtained at the dclimit, EIS contains more information about the system since it is acquired in a wide range of frequencies. In this work, Zr dissolution in HF was investigated using electrochemical impedance spectroscopy and the data was analyzed in the frame work of reaction mechanism analysis. A rotating disk zirconium electrode (5×4 mm) was used in a standard three electrode cell with Ag/AgCl (in 3.5 M KCl) as reference and Pt wire as counter electrode. PARSTAT 2263 (AMETEK) was used as the electrochemical work station and electrode was rotated at 900 rpm (Pine Instruments). The electrochemical impedance data was obtained by superimposing a small amplitude ac potential perturbation of 10 mV rms on the dc potential in a frequency range of 100 kHz to 0.1398 Hz. EIS measurement was performed on Zr dissolving in 10 HF solutions with 0.1 M Na2SO4 as supporting electrolyte. The EIS spectra was acquired at two different dc potentials in the active region (0.075 and 0.1 V vs. OCP) and at two different dc potentials in the passive region (0.5, 0.8 V vs. OCP). These dc potentials were chosen from the corresponding polarization curves. The morphology of the surface was analyzed using atomic force microscopy (AFM). Figure 1a and Fig. 1b shows the spectra observed in the active and passive region, in 10 mM HF. Impedance spectra in the active region show three loops with an inductive loop in the low frequency end. In the passive region, an inductive loop and a capacitive loop is observed in the mid frequency region and an apparent negative resistance and capacitance in the low frequency end. The observed EIS spectra were validated using Kramer's Kronig Transform (KKT). The spectra were modelled using electrochemical equivalent circuit (EEC) containing three Maxwell elements and the circuit parameters were calculated. A four step mechanism with two intermediates was able to predict most, but not all, of the major features observed in the impedance spectra. The number of Maxwell elements required to model the spectra indicate that at least one more adsorbed intermediate should be incorporated in the mechanism to explain all the features observed.

Electrochemical impedance spectroscopy (EIS) is a well-known technique that has been employed on various electrochemical cells in order to obtain their impedance spectra. Lithium-ion cells are some of these cells to which it has been applied. The impedance spectra obtained from EIS can be used to estimate various battery state of health (SOH) and state of charge (SOC) characteristics. The lengthy acquisition time associated with standard EIS makes it unsuitable for rapid on-line impedance measurements. Alternative methods that take a shorter time have therefore been proposed. This paper compares the spectra obtained by Harmonic Compensated Synchronous Detection (HCSD) broadband signal technique with EIS and a custom Broadband Impedance Spectroscopy (BIS) technique at different DC bias currents which mimic a real time load. The test cells are industry standard Nickel-Cobalt and Manganese Oxide (NCM) lithium-ion cells. The BIS technique is similar to HSCD in the selection of frequencies however the amplitude of the excitation broadband signal is varied to match the impedance magnitude response of the cell. Also, parameter extraction is performed on both EIS and BIS for fault detection purposes.

Accelerated state of health estimation of second life lithium-ion batteries via electrochemical impedance spectroscopy tests and machine learning techniques

Electrochemical impedance spectroscopy (EIS) is one of the most important non-destructive diagnosis tools in lithium-ion battery (LIB) technology. EIS is routinely used for characterization of battery materials, optimization of manufacturing processes, and understanding of degradation mode. However, interpretation of EIS spectra is not a straightforward procedure. Typical EIS data of LIB have heavily overwrapped capacitive semicircles in Nyquist (complex impedance) plot because LIBs’ anodes and cathodes both involve several conduction processes. Widely used method for information separation is least-squares fitting based on discrete equivalent circuit model. However, this method requires a priori assumption on the number of capacitive processes. Destructive EIS measurement methods, such as insertion of reference electrode and symmetry cell construction, are powerful for separation of cathode/anode information. But these involve meticulous work, and battery structure or degradation state often make it difficult to obtain an accurate measurement result.Recently, distribution of relaxation times (DRT) analysis has increasingly used for EIS interpretation. This analysis treats an EIS spectrum as a continuous function of relaxation time, or time constant of infinitesimal RC equivalent circuit element. DRT analysis can distinguish several different capacitive processes without the need of prior model assumption. Application field of DRT analysis currently focuses on solid oxide fuel cell, but several LIB studies have been reported for LiFePO4 cathode system[1] and LiMn2O4-LiNixCoyMnzO2 cathode system[2]. Here we demonstrate that DRT analysis is a powerful tool for degradation analysis of LIBs with LiCoO2(LCO)-based cathode and graphite anode, and provide experimental verification of information obtained by DRT analysis.Commercial-size prototype LIBs with LCO-based cathode and graphite anode are used for this work. Charge-discharge cycling tests of the cells are performed at different temperature conditions. EIS measurements are conducted at fully charged state of every fifty cycles, with frequency range of 1 MHz to 10 mHz. For better separation of different processes, the EIS spectra are obtained at 23 deg C, 10 deg C and 0 deg C in a climate chamber. DRT is calculated by MATLAB with in-house code, which is based on Fourier transfer methods utilizing window function preprocessing[3]. To understand DRT results in physical viewpoints, several electrode analyses of disassembled cells are conducted at initial and the cycled state. Figure 1 shows Nyquist plots and the corresponding DRT plots of (a) low-temperature and (b) high-temperature cycled LIBs obtained at 10 deg C. In Nyquist plot, all spectra exhibit the shape of two depressed capacitive semicircles. At a first glance, both low-temperature cycling and high-temperature cycling appear to increase the size of low-frequency semicircles. But closer look shows that low-temperature cycling cause “merge” or heavier overwrap of two semicircles, whereas high-temperature cycling retains the separated feature. These characteristics are further clarified by DRT analysis. In each cell, we can identify four different peaks in DRT plots. The high-temperature cycled cell shows gradual increase in the lowest-frequency (1) peak, whereas the peak remains almost the same intensity in the low-temperature cycled cell and the middle-frequency (2) peak increases significantly. No change is observed for the (3) peak during the cycle test. Both cycling condition cause the increase in the highest-frequency (4) peak. Further teardown analyses verify that these DRT peaks can be attributed to different electrode degradation phenomena, which are related to cycling temperature. These results demonstrate the ability of DRT analysis as a degradation diagnostics tool for LIBs with various kinds of material systems. [1] J. P. Schmidt, T. Chrobak, M. Ender, J. Illig, D. Klotz, E. Ivers-Tiffée, J. Power Sources, 196 5342 (2011). [2] B. Stiaszny, J. Ziegler, E. Krauß, J. P. Schmidt, E. Ivers-Tiffée, J. Power Sources, 251 439 (2014).[3] H. Schichlein, A. C. Müller, M. Voigts, A. Krügel, E. Ivers-Tiffée, J. Appl. Electrochem., 32 875 (2002). Figure 1

As the energy storages in the renewable energy system, lithium ion battery (LIB) is one of the promising storage devices because of its high energy density and high power output. Diagnosis technology of LIBs is very important to use electric devices in safety as well as development of materials. Since early times, Professor Bruno Scrosati group and our group have collaborated to develop battery systems, consequently a rechargeable all-solid lithium/polypyrrole (PPy) polymer battery was demonstrated. [1] We introduce the Li batteries and its diagnosis system while appreciate his contribution in the field of batteries. To increase the energy density of LIB, it is important to keep the capacity balance of the cathode and anode. Even if the capacity of only one electrode increased, it is not possible to increase the energy density of LIB. Such a capacity balance of electrodes is calculated as the battery on the basis of a silicon-based anode and a sulfur-based cathode. It is important as the reactive silicon anode to overcome the problem that the large volume change during charging and discharging to encourage the cyclability, thus we developed a Si-O-C composite anode, which is prepared by the reduction of silicon source and organic solvent. The Si-O-C composite anode was composed of SiOx (0<x<2) and C from organic compounds, resulting in buffering the volume change of silicon. The Si-O-C composite anode delivered high discharge capacity of ~800 mAh/g of Si even after 7000 cycles. [2] The Si-O-C composite anode was evaluated as a full cell by combining with Li2S cathode developed by Professor Bruno Scrosati group. At that time, this battery is one of the rare examples of lithium-metal-free sulfur battery. [3] As for the sulfur-based cathode, it is the key issue to overcome the problem of lithium polysulfide dissolution, which result in capacity fading and lowering of the charge-discharge efficiency. We demonstrated one of the solutions as the coating sulfur electrode with a PPy film, which is prepared by oxidative electro-polymerization.[4] The simple structure prepared by directly coating the PPy film on the sulfer cathode, enabled the suppression of polysulfide dissolution into the electrolyte, thereby inhibiting the shuttle phenomenon. Therefore, it is one of the attractive methods to work sulfur cathode, since this allows the flexibility of choosing electrolytes according to the choice of the anode. Electrochemical impedance spectroscopy (EIS) is superior method for analysis of the battery health while in use. EIS has been utilized to characterize each factor of batteries, because it enables us to analyze dynamics of each elemental step sensitively and separately without destruction of the cell. In addition, un-destructive EIS is expected to utilize for premonitory diagnosis of batteries on board in electric vehicles. In our previous study, the equivalent circuit to express each elemental step in a commercial LIB by EIS has been carefully investigated. We proposed the designed equivalent circuit, and on the equivalent circuit, the impedance responses of LIB during capacity fading were analyzed with continuous charge-discharge cycling. EIS using conventional FRA – potentiostat systems is not easy to measure the impedance of the large-scale LIB because of its low internal resistance. Moreover, FRA – potentiostat system for conventional EIS measurement could not be mounted on the vehicle. Thus, impedance measurement system is needed without using FRA – potentiostat systems. In our study, application of square wave potential for input signals of EIS was investigated in simple electrochemical reaction to verify a new technique called “Square-potential/current electrochemical impedance spectroscopy (SP-EIS, SC-EIS)” which is a method for EIS without using the FRA systems. We applied SC-EIS to evaluate a state of a commercial LIB. Introduction of SC-EIS to diagnosis technology of laminated LIBs and the LIB module was discussed. [5]

Lithium-ion batteries have been very successful in consumer electronics as viable and efficient power sources for many small and portable devices such as mobiles, laptop, watches, camcorders, PDAs, cameras and other communication devices [1-2]. However, poor electronic conduction in electrodes due to an unstable and fragile conducting network of traditional conducting additives is still the limitation for large scale commercialization of this energy storage technology in automotives (such as EVs, HEVs, PHEVs, etc.) where high power density is desired frequently [2, 3]. In addition, poor contact due to large size of active material and sluggish kinetics makes it difficult to achieve their full theoretical capacities at a practical level [4]. The conducting network in an electrode influences the performance of charge transfer kinetics at the electrode-electrolyte interface and ion migration through the solid electrolyte interface (SEI) layer as suggested by an earlier study [5]. In graphitic anode, when an ion of lithium is inserted into the material, the crystal structure of the active material changes with the state of charge (SOC), and the resulting changes affect the intercalation/deintercalation reactions [6].In this work, we investigate the kinetics of lithium-ion transfer for mesocarbon mocrobeads (MCMB) as active material with nano-conducting fillers, namely carbon black (CB) and multiwalled carbon nanotubes (MWCNT), by carrying out electrochemical impedance spectroscopy (EIS) measurements at different states-of-charge (SOC) and temperatures for CR2016 coin half-cells. The working electrodes were fabricated with 88% MCMB, 4% conducting additives and 8% PVDF coated on copper foil. It has recently been demonstrated that a synergistic improvement in electrical and electrochemical performance occurs with partial substitution of CB by CNT [7]. By recording impedance spectra at different temperatures and SOCs for electrodes having different conducting additives (CB, CNT or CB+CNT), we analyse the impact of conducting nano-fillers upon the kinetics of the anode reactions and the dependency of these on the SOC. The impedance spectra were measured at the set SOC with an AC perturbation of amplitude 5mV in the range 30mHz to 200kHz. The conductivity of interfacial charge transfer (1/Rct) obeys the Arrhenius equation, 1/Rct=A0exp(Ect/RT). The symbols A0, Ect, R and T stand for frequency factor, activation energy, gas constant and absolute temperature. A typical EIS spectrum of MCMB electrode in a lithium-ion half-cell and the respective resistances deconvoluted using an equivalent circuit is demonstrated in Fig. 1(a). Impedance spectra plotted at different temperatures for MCMB electrode having 4% CNT as conducting additives at OCV of 0.17V vs. Li/Li+ are illustrated in Fig. 1(b) and the corresponding Arrhenius plot of interfacial conductivity (1/Rct) obtained from impedance plot is shown in Fig. 1(c). The activation energy of charge transfer as a function of SOC and open-circuit potential is illustrated in Fig. 1(d). The lithium-ion staging process in MCMB electrode is highlighted by vertical lines as shown in Fig. 1(d). From Fig. 1(d), the variation in activation energy can be attributed to the insertion/deinsertion of lithium ions into carbon and the chemical nature of the solid-electrolyte interphase (SEI) layer deposited on the surface of the active material. The activation energy associated with Rct tends to decrease with the potential and vary with different conducting nano-fillers. This indicates that the staging phenomenon and SEI composition affect the charge transfer process. It is observed that the activation energy in stage-I is relatively high than the other stages which is attributed to the large structural change associated with lithium-ion insertion/deinsertion in this stage. For comparative analysis, the activation energy for the interfacial Li-ion transfer in electrodes having conducting additives CB, and CB+CNT will be evaluate. Moreover, Arrhenius plot for the Li-ion transport conductivity through the SEI layer and the corresponding activation energy at different SOC will also be discuss in order to better understand the reaction kinetics in MCMB carbon electrode with different conducting nano-fillers.

Lithium ion batteries have the issue of internal short circuiting by the electrodeposition of metal at the negative electrode. This deposition follows the dissolution of contaminated metal particles incorporated into the positive electrode in manufacturing process. Thus, we have investigated the dissolution­/deposition behavior of metals such as copper, nickel, iron, and stainless steel so far1. We also proposed a diagnosis method for the incorporation of the metal particles by electrochemical impedance spectroscopy, taking advantage of characteristic changes of the impedance spectra (phase angle) between 10-­1 Hz1. In the present study, we investigate the time variation of the impedance spectra associated with the growth of the metal deposits at the negative electrode. Test cells were assembled with positive electrodes of metal plates of iron, nickel and stainless steel, electrolyte solution of ethylene carbonate (EC)/diethylcarbonate (DEC) (1:1 vol.) containing 1 M LiPF6, and negative electrodes of graphite mixed with PVDF binder. Potential between the metal plates and the negative electrode was maintained at 4.2 V by a potentio/galvanostat to electrochemically dissolve the metal plate at the positive electrode and deposit the metals at the negative electrode, while the negative electrode was maintained at 0.3 V against a lithium wire in the test cell by an auxiliary potentio/galvanostat to reproduce the potentials in a lithium ion battery. We observe the metal deposits at the negative electrodes from the iron, nickel and stainless steel plates by FE-SEM and EDX. Time variations of the phase angle in the impedance spectra between 10­-1 Hz for the above metal deposits are correlated with the metal growth, taking into account the impedance of the SEI layer at the metal surface. 1. Hironori Nakajima, and Tatsumi Kitahara, Diagnosis Method to Detect the Incorporation of Metallic Particles in a Lithium Ion Battery, ECS Trans., Vol. 68, 2, 59-74 (2015).

Lithium ion batteries have gained increasing attention in the last two decades. Perfoming electrolyte additive into lithium ion battery could enhance the baterry performance. However several studies on electrolyte additive only show the experimental data. The behavior of battery kinetic inside the battery and the ionic diffusion during operation was not analyzed. This study will investigate the effect of electrolyte additive on ionic diffusion of battery based on electrochemical model. The role of the electrolyte is to provide an ionic conduction path between the anode and the cathode. This study elucidates the improvement of the cycleability by performing the electrolyte containing 0.1 wt % of Flouro-o-phenylenedimaleimide (F-MI) based additive compared to the electrolyte with 0.1 wt % N,N’-o-phenylenedimaleimide (O-MI) and without an additive shown by effective constant phase elements (CPE) coefficient of impedance spectra on electrochemical impedance spectroscopy (EIS). The result elucidates that many amount of lithium ion remains on SEI layer of the mesocarbon microbeads (MCMB) half cell with F-MI additive, indicating that ion move easily because of high diffusion. The simulation result elucidated the agreement with the experimental data, the diffusion of the MCMB half-cell with F-MI additive is highest compared to MCMB half-cell with O-MI and without additive, that is emphasized with result on the EIS test.

Estimating the parameters of lithium-ion (Li-ion) batteries under dynamic working conditions is a critical challenge in the health management of electrical energy storage systems. This paper estimates the equivalent circuit model (ECM) parameters and analyzes the influence of different factors on the Li-ion batteries impedance using the electrochemical impedance spectroscopy (EIS) technique. Firstly, the influence of the temperature, state of charge (SOC) and number of charging/discharging cycles on the impedance spectrum was studied. Nyquist plots were used to perform this analysis. Subsequently, ECMs were used to characterize the Li-ion batteries under study at different operating conditions. Specifically, the ECM parameters were estimated using the gaining-sharing knowledge (GSK) metaheuristic algorithm, allowing the consequent estimation of the impedance spectra obtained by the EIS technique. Experimental results included 15 datasets measured experimentally at three temperature levels for five SOCs and different number of charging/discharging cycles. To investigate the variation of Li-ion battery parameters with cyclic aging 350 datasets from the literature were also used. The results showed that the impedance and model parameters depend considerably on the considered factors. The estimation of the ECM parameters demonstrated high accuracy and reliability (mean RMSE values of 4.32E-02 and 2.33E-02 and mean STD values of 3.38E-16 and 5.82E-13 with measured and literature datasets, respectively), allowing the robust determination of the numerous impedance spectra under study.

With dwindling fossil resources and growing environmental concerns, clean and efficient energy conversion and storage technologies are getting more and more attention from the public. Lithium ion batteries, redox flow batteries as well as fuel cells hold the promise and burden to sustain our energy-demanding society. In recent years, several efforts have been addressed to vanadium redox flow batteries (VRFB) which show great promise for the economical storage of electrical energy intermittently available from wind and solar. The excess energy is stored in liquid electrolytes using the four oxidation states of Vanadium, V2+/3+ at the negative, V4+/5+at the positive side. The liquid electrolytes flow through porous carbon felt electrodes, which provide a heterogeneous reaction surface. The main reasons to use carbon felts are their corrosion resistance in acidic electrolyte, high overpotential towards the unwanted hydrogen evolution reaction (HER) and low material costs. In addition, their activity towards the positive and negative reaction, respectively, can be modified using thermal oxidation in air atmosphere, acid treatment, heteroatom doping, and others. With respect to stationary applications with projected system runtimes of 10˙000 hours and more, not only activity, but also durability of the electrode materials moves into the focus of current research. It has been reported [1] that the carbon felts undergo significant degradation when cycled for a certain number of times. However, already the electro-less contact with the highly acidic electrolytes seems to affect the felts properties. In this study, static electro-less ageing and dynamic degradation of heat-treated carbon felt electrodes were investigated by combining different electrochemical and analytical methods. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to monitor the performance loss of the carbon-based electrodes, whereas scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were applied to study cause and effects of material’s degradation. In this respect, oxygen functional groups, electron conductivity, wettability, accessible surface area and other characteristics play an important role. In general, the HER is a parasitic reaction, which should be hindered in favor of the V3+ reduction. It has been reported that bismuth additions to the electrolyte enhance the activity of the felt for the negative reaction without enhancing the HER [2]. However, the competition between HER and V3+reduction can also be used as an indicator of the felt’s state of health when probed at different temperatures and in different electrolyte concentrations. We will discuss this for differently degraded felts. Furthermore, we use our battery tester with implemented reference electrodes to compare the individual half-cell potentials with full cell potentials and to study the effect of different cut-off voltages on the projected electrode degradation. Higher cut-off potentials might prove effective for the system’s operation strategy, if they do not lead to the expected increased degradation phenomena. [1] I. Derr, M. Bruns, J. Langner, A. Fetyan, J. Melke, C. Roth „Degradation of all-vanadium redox flow batteries (VRFB) investigated by electrochemical impedance and X-ray photoelectron spectroscopy: Part 2 electrochemical degradation, Journal of Power Sources 325 (2016) 351-359. [2] B. Li, M. Gu, Z. Nie, Y. Shao, Q. Luo, X. Wei, X. Li, J. Xiao, C. Wang, V. Sprenkle, W. Wang Nano Letters. 13 (2013) 1330-1335.

The measurement and determination of the lithium ion battery's electrochemical impedance spectroscopy (EIS) and the application of EIS to battery classification are researched in this paper. The lithium ion battery gets extensive applications due to its inherent advantages over other batteries. For proper and sustainable performance, it is very necessary to check the uniformity of the lithium ion batteries. In this paper, the equivalent circuit of the lithium ion battery is analyzed; the design of hardware circuit based on DSP and software that calculates the EIS of the lithium ion battery is critically done and evaluated. The parameters of the lithium ion equivalent circuit are determined, the parameter values of li-ion equivalent circuit are achieved by least square method, and the application of Principal Component Analysis (CPA) to the battery classification is analyzed.

Electrochemical impedance spectroscopy (EIS) is a powerful diagnostic tool used in a wide range of applications, including solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs). While EIS measurements on single cell level are commonplace, implementation of EIS on stack level remains limited, primarily due to the extremely low impedance of large-footprint cells, which imposes stringent demands on the impedance spectrometer and experimental setup (1). Furthermore, compared to single-cell EIS data, stack-level data reported in the literature are rarely subjected to the same degree of equivalent circuit modeling, making a detailed analysis of underlying electrochemical processes difficult.Here, we report a framework for analyzing stack-level impedance spectroscopy data. The quality of the acquired data is first verified using Kramers-Kronig transformations (2), followed by the application of distribution of relaxation times (DRT) and analysis of the difference of impedance spectra (ADIS) methods to experimental data collected under a set of pre-determined operating conditions (electrochemical test procedure) (3-4). DRT and ADIS results were incorporated into the complex non-linear least squares (CNLS) fitting procedure and the validity of the chosen equivalent circuit model was confirmed by reconstruction of Nyquist, Bode, the individual electrochemical contributions, and DRT plots of the fitted data.The developed framework was successfully implemented on a commercial 75-cell SOEC stack (TSP-1) developed by Haldor Topsoe (5). An electrochemical impedance spectrum is recorded simultaneously on all 13 cell groups in the stack using Zahner instrumentation. In this work, the electrochemical impedance data obtained from a state-of-the-art TSP-1 stack, containing three different types of Ni/YSZ based cells, is reported. The stack was initially investigated by EIS, using an electrochemical test procedure including CO2 electrolysis under constant conversion, H2O electrolysis under constant conversion, variations in the pO2 on the oxygen electrode, and finally temperature variations in CO2 electrolysis operation. This electrochemical test procedure was performed to develop an equivalent circuit model for the stack. Afterward, the stack was subjected to a degradation in steam electrolysis under 580 mA/cm2 (70% conversion), with an impedance spectrum being recorded every 24 hours. The operational point for this degradation test was chosen to match the real-life operation point of these stacks and hence to give a realistic image of any potential degradation. The developed framework and the equivalent circuit model developed for the stack was finally used to model the EIS data obtained during the degradation test. The modeling of these EIS data utilizes the full potential of electrochemical impedance spectroscopy and help identify any degradation mechanisms taking place in the stack, an analysis not previously reported on stack level.(1) R. R. Mosbæk, J. Hjelm, R. Barfod, and P. V. Hendriksen. ECS transactions, 35, 1 (2011).(2) B. Boukamp, J. Electrochem. Soc., 142, 1885 – 1894 (1995).(3) S. H. Jensen, A. Hauch, P.V. Hendriksen, M. Mogensen, N. Bonanos, and T. Jacobsen. Journal of the Electrochemical Society, 154(12), B1325-B1330, (2007)(4) H. Schichlein, and E. Ivers-Tiffee. Journal of Applied Electrochemistry, 32, 875-882, (2002).(5) J. Rass-Hansen, P. Blennow, T. Heiredal-Clausen, R. Küngas, T. Holt Nørby, and S. Primdahl, Proceedings of the 12th European SOFC & SOE Forum, 318-325 (2016). Figure 1