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(a) Electrode stacks for positive/positive, negative/negative, and negative/positive coin cells each consisting of two double-sided electrodes and a separator. (b) The electrode stack of a pouch cell containing double-sided positive and negative electrodes separated by a separator; electrodes for the coin cells were punched directly from pouch cell double-sided electrodes. (c) A cross-section of a coin cell containing an electrode stack, within a metal can and cap, with a metal spring and spacer to provide pressure. Note that the metal contacts are in contact with the electrode material. (d) A schematic section of a pouch cell jelly roll (only 2 turns are shown) with the metal tabs connected directly to aluminum foil and copper foil current collectors.
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Measuring electrochemical impedance spectra of lithium-ion symmetric cells at low temperatures allows for unambiguous separation of charge transfer impedance contributions from other cell impedance features. Electrodes from dry Li[Ni0.5Mn0.3Co0.2]O2 (NMC 532)/artificial graphite (AG) pouch cells were used to make blocking electrode configuration sy...
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... symmetric cell assembly process can be seen in detail in Petibon et al. 19 The electrodes used in the symmetric cells were two-side coated, not single side coated. Figure 1 compares the electrode stacks in positive/positive, negative/negative and negative/positive coin cells to the electrode stack in a pouch cell. Figure 1 shows that there is an extra layer of electrode material (the coating on the back side of the electrode) between the foil current collector and the coin cell casing that is not present in the pouch cell. ...
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... 1 compares the electrode stacks in positive/positive, negative/negative and negative/positive coin cells to the electrode stack in a pouch cell. Figure 1 shows that there is an extra layer of electrode material (the coating on the back side of the electrode) between the foil current collector and the coin cell casing that is not present in the pouch cell. It was determined that the additional layer of electrode material does not affect the mid to low frequency "semicircle" in the EIS spectrum associated with R ct . ...
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... the extra layer of electrode material does amplify the high frequency contact resistance. Figure S1 shows a comparison between doublesided and single-sided symmetric cells demonstrating the similarity in R ct and the difference in contact resistance. Additionally, a comparison of double-sided full coin cells to a pouch cell can be seen in Figure S2. ...
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... lithium-ion desolvation must be a minor contributor to R ct . Fig- ure S10 shows an example of the consistency of the contact impedance while R ct varies with the addition of VC to the electrolyte. Figure 7 shows the linear relationship between the logarithm of the charge transfer resistance and the inverse of temperature for four non-blocking cells that underwent formation to different voltages. ...
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... 7 shows the linear relationship between the logarithm of the charge transfer resistance and the inverse of temperature for four non-blocking cells that underwent formation to different voltages. The charge transfer resistance follows the Arrhenius equation (Equation 1), showing that R ct increases exponentially with decreasing temperature. Activation energy values can be extracted from this data and values are indicated in the legends in Figure 7. ...
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... all cases the values of φ in the fits for negative electrode symmetric cells were between 0.4 and 0.8 while the values of φ were between 0.7 and 1.0 for positive electrode symmetric cells. In our model of the charge transfer impedance, the layers of positive and negative charge are formed at the active material side of the SEI and the outer Helmholtz plane, which can be seen in Figure S11. The formula for the capacitance of a parallel plate capacitor is: ...
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Citations
... The double-sided electrodes were directly used, instead of removing one side from the current collector, since previous studies showed that the backside does not affect EIS measurements of the coin cells. 33,34 From these six negative electrodes and six positive electrodes, 3 positive electrode symmetric coin cells (+/+) and 3 negative electrode symmetric coin cells (-/-) were assembled using the same electrolyte formulation as the parent pouch cell. Two pieces of 3501 Celgard were used as the separator in the coin cells. ...
This study explores the impact of simple electrolyte additives on the performance of layered oxide/hard carbon sodium-ion pouch cells. The cycle life of these cells between 2.0 and 3.8 V is assessed at various temperatures (20, 40, and 55 °C) with different solvent systems based on ethylene carbonate, diethyl carbonate, and dimethyl carbonate. A particular challenge in these cells is gas generation at high temperature. Pouch bag experiments which separate the charged electrodes to measure their gas generation from reactions with the electrolyte show that hard carbon generates no gas, but the sodium layered oxide produces large amounts of gas. Isothermal microcalorimetry corroborates these results with parasitic heat flow measurements of pouch bags and full pouch cells. A crosstalk mechanism is revealed which lowers gas generation and reduces parasitic heat flows in full cells. The electrolyte additives prop-1-ene-1,3-sultone, sodium difluorophosphate, and 1,3,2-dioxathiolane-2,2-dioxide (DTD) are effective at reducing gas generation and heat flow from the positive electrode. They also reduce self-discharge in elevated temperature storage tests. Overall, 1 M NaFSI in EC:DMC (15:85) with 2% DTD is the best electrolyte for the sodium-ion pouch cells in this work. Eventually, the performance of these cells is compared to optimized LiFePO4/graphite cells.
... These findings point out that among the four samples, AG-2 possesses the fastest kinetics. 9 Electrochemical property of 18650 cylindrical cells.- Figure 8 highlights the performance of commercial graphite electrodes subjected to charging at a rate of 0.5 C and discharging at various C-rates. Figure 8A focuses on the specific capacities of these electrodes across different C-rates. ...
We conducted a detailed evaluation of the electrochemical performance of artificial graphite (AG) and natural graphite (NG) from four leading global companies: AG-1, AG-2, AG-3, and NG-4 towards Ni-rich Li-ion batteries. We found that AG-2, an artificial graphite variant, demonstrated superior performance with exceptional capacity, rapid charging capabilities, and impressive capacity retention. AG-2 achieved a specific capacity of 338.97 mAh g⁻¹, outperforming AG-1 (321.16 mAh g⁻¹), AG-3 (314.43 mAh g⁻¹), and NG-1 (328.08 mAh g⁻¹). This superiority was further confirmed by high C-rate tests ranging from 2 C to 5 C. Notably, after 500 cycles, AG-2 maintained 91.18% of its initial capacity, significantly surpassing AG-1 (89.44%), AG-3 (78.78%), and NG-1 (84.16%). The study attributes AG-2’s exceptional performance to its refined properties such as smaller particle size, fewer graphite imperfections, and a higher 2H phase content. These characteristics lead to increased active material in the anode, enhancing battery capacity, and to less material degradation over time, ensuring consistent capacity retention. Overall, AG-2 stands out as a highly efficient and cost-effective option for lithium-ion battery applications, eclipsing other commercial graphite alternatives.
... The double-sided electrodes were directly used, instead of removing one side from the current collector, since previous studies showed that the backside does not affect EIS measurements of the coin cells. 12,13 From these nine negative electrodes and nine positive electrodes, 3 full coin cells (+/−), 3 positive electrode symmetric coin cells (+/+) and 3 negative electrode symmetric coin cells (−/−) were assembled using the same electrolyte formulation as the parent pouch cell. Two pieces of 3501 Celgard were used as the separator in the coin cells. ...
... symmetric cell impedance spectroscopy, the real part, Z(Re), and imaginary part, -Im(Z), of the full cell (+/−) can be calculated as the sum of half the positive/positive [(+/+)/2] and half the negative/ negative [(−/−)/2] symmetric cell impedance. 12,13 In Nyquist plots, we interpret R ct as the width of the semi-circle feature; in Bode plots, as a step in the Re(Z) vs frequency curve or a bell-shaped peak in the -Im(Z) vs frequency curve. Our previous study on symmetric cell electrochemical impedance spectroscopy of layered oxide/hard carbon Na-ion pouch cells showed that the negative electrode R ct is substantially larger than the positive electrode R ct . ...
This study examines the influence of electrolyte salts and solvents on the performance of O3 layered oxide NaMn0.39Fe0.31Ni0.22Zn0.08O2/hard carbon sodium-ion pouch cells with polyethylene terephthalate (PET) jellyroll tape. A significant enhancement in cell performance between 2.0 and 3.8 V was observed across various temperatures (20, 40, and 55 °C) by substituting NaPF6 with NaFSI, including reduced impedance growth, minimized gas generation, and supressed jellyroll tape decomposition. Ultra-high precision coulometry revealed that the use of NaPF6 resulted in increased unwanted parasitic reactions associated with tape decomposition, e.g., capacity fade and charge endpoint capacity slippage. Teardown of sodium-ion pouch cells after cycling in DMC-based electrolytes revealed a severe decomposition of the PET tape with NaPF6 but not with NaFSI. Gas chromatography shows significantly more electrolyte decomposition products with NaPF6 as opposed to NaFSI. DEC-based electrolyte showed less capacity fade, less electrolyte decomposition products, and less tape decomposition after cycling than DMC-based electrolyte. The electrolyte additive DTD can prevent parasitic reactions in DMC- and NaPF6-based electrolyte. Overall, the choice of salts and linear carbonates in alkyl carbonate electrolytes plays a crucial role in determining the overall cycling performance of the layered oxide/hard carbon sodium-ion cells with PET jellyroll tape.
... These outlier trends are probably due to the fact that the respective EIS measurements were performed after an incorrect charge cycle and, consequentially, the SOC of the cell analyzed was much lower than 100% [43] (for the battery discharged at a 3C-rate, this behavior is also associated with an average temperature higher than during the measurements of the other cell [44]). ...
In the era of Industry 4.0, achieving optimization in production and minimizing environmental impact has become vital. Energy management, particularly in the context of smart grids, plays a crucial role in ensuring sustainability and efficiency. Lithium-ion batteries have emerged as a leading technology for energy storage due to their versatility and performances. However, accurately assessing their State of Health (SOH) is essential for maintaining grid reliability. While discharge capacity and internal resistance (IR) are commonly used SOH indicators, battery impedance also offers valuable insights into aging degradation. This article explores the use of Electrochemical Impedance Spectroscopy (EIS) to define the SOH of lithium batteries. By analyzing impedance spectra at different frequencies, a comprehensive understanding of battery degradation is obtained. A life cycle analysis is conducted on cylindrical Li–Mn batteries under various discharge conditions, utilizing EIS measurements and an Equivalent Circuit Model (ECM). This study highlights the differential effects of aging on battery characteristics, emphasizing the variations at different life stages and the behavior changes on each region of the impedance spectrum. Furthermore, it demonstrates the efficacy of EIS and the advantages of this technique compared to the solely IR measurements used in tracking SOH over time. This research contributes to advancing the understanding of lithium battery degradation and underscores the importance of EIS in defining their State of Health for Smart Grids applications.
... 28,[32][33][34][35][36][37][38] Other groups argue that the two processes referring to charge transfer and SEI cannot be distinguished based on the characteristic frequency, unless further analysis, i.e. blocking conditions are applied. [39][40][41] To assign the polarization processes found in our work, we evaluated the activation energies (E A ) of the identified processes and compared them with the values reported by Illig et al. who analysed graphite anodes using transmission line models and distribution of relaxation time analyses. 42 For the low-frequency semicircle (R 2 |CPE 2 ) we found an E A of 70 kJ mol −1 , which is in good agreement with the values reported for both the charge-transfer resistance (R ct ) and the SEI resistance (R SEI ) (76 kJ mol −1 and 70 kJ mol −1 , respectively). ...
Prelithiation is widely recognized as a promising technology to enable the use of high capacity anode active materials such as silicon. Numerous prelithiation techniques have been proposed over the years, with a handful successfully undergoing pilot scale testing. Nevertheless, new challenges arise when moving from optimizing single processes to integrating them into the process chain. A major concern is the stability of prelithiated electrodes against moisture. In this study, we investigated the influence of industrially-relevant moisture levels on the electrochemical performance of prelithiated graphite/SiOx composite anodes in 3-electrode half- and full-cells. We identify several indicators of electrode degradation such as an increase in open circuit potential, a decrease in graphite lithiation potential, and changes in specific charge/discharge capacity. The underlying degradation mechanisms are investigated using electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry, which show increased solid electrolyte interphase (SEI)-related interfacial resistances but no clear evidence of SEI degradation. Based on the experimental results, we define a process window for the stability of the investigated electrodes as a function of dew point and exposure time. Our results indicate an encouragingly high stability at dew points up to -40°C for a realistic exposure time of 1 hour
... The frequency of the third cathode peak τC3 increases with temperature (from 20Hz to 43 Hz), i.e. resistance decreases with temperature rising. The charge transfer resistance normally shows the most significant dependency on the temperature [47,48] and hence, τC3 was identified as cathodic charge transfer. We believe that, in this work, the τC3 response is a combination of charge transfer and CEI for NMC811. ...
The role of 2 wt% triallyl phosphate as an electrolyte additive in (NMC811)/SiOx-graphite 1Ah pouch cells is studied using electrochemical impedance spectroscopy, long-term cycling, rate, timescale characterisation and X-ray photoelectron spectroscopy. Six kinetic processes are identified within the 100 kHz to 0.01 Hz frequency range. Anode processes consistently occur faster than the cathode and at higher frequencies. The triallyl phosphate (TAP) additive improves capacity retention from 70% to 85% after 500 cycles at 45 °C, exhibiting a higher and more stable coulombic efficiency, with ∼100% reduction in DCIR growth. TAP cells produce less gas during cycling. Timescale characterization suggests that the high impedance in the base formulation originates from cathodic charge transfer and cathode electrolyte interface (CEI) films in non-TAP-containing samples. The XPS data confirm the DRT findings, indicating the presence of high-impedance species associated with solvent oxidation and transition metal oxides (TMO) in the CEI of the TAP-free sample. The initial higher impedance of 14%–0.06 Ω observed in TAP cells is due to the formation of a thicker CEI in the TAP samples. Consequently, TAP samples show a ∼10 mAhg−1 lower rate capacity, at higher C-rates of 3C and 5C, while both samples exhibit consistent rate-capacity retention.
https://authors.elsevier.com/a/1io9Q1M7w0emh%7E
... 24 In their study, Keefe et al. conducted EIS experiments on symmetric cells comprising two positive electrodes (NMC cathode) or two negative electrodes (graphite), as well as full cells with positive/negative or NMC/graphite configurations. 25 The EIS spectra of the positive and negative electrodes exhibit two-loop features that are comparable to each other. The complete EIS spectrum of the full cell is the combination of the two individual spectra, as illustrated in Fig. S5 of the supplemental information. ...
... On the other hand, the high frequency loop (smaller semicircle) represents the charge transfer region of the active material grains and the current collector. 25,30 Regardless of how the overall EIS is interpreted, it is evident that the desolvation of complexed Li + ions and diffusion of Li + through the SEI are significant factors contributing to the charge transfer resistance, and ultimately determine the size of the low (and perhaps high) frequency semicircle loops in the EIS spectra. ...
... The dielectric constant of the solid electrolyte interface (SEI) layer is related to its composition, which should remain similar across all cells because of the consistent electrolyte makeup. 25 Furthermore, the other variables in Eq. 3 remain constant. As a result, any variations in the double layer capacitance can be associated with changes in the thickness of the SEI layer. ...
We provide compelling evidence that the cycling performance of 18650 Li-ion cells is adversely affected by excessive amounts of electrolyte volume, with a noticeable decline observed within the initial 30 cycles, particularly at higher discharge rates. This "high-volume effect" imposes additional constraints on the optimization of cell manufacturing, highlighting the importance of identifying its underlying causes. The electrochemical impedance of 3.5 Ah 18650 cylindrical cells with varying levels of electrolyte volume was extensively measured using PEIS and GEIS techniques. The results indicate that, in general, the ohmic and charge transfer resistance(s) of the cells increase at a faster rate when excess electrolyte volume (9% and 18%) is present. During high discharge rate cycling, relaxation periods can effectively recover the lost capacity, but when high discharge rate cycling resumes, the trend in the capacity loss reappears. We hypothesize that a salt segregation effect in the electrolyte may contribute to the growth of both ohmic and charge transfer resistance, leading to capacity loss when excess electrolyte is present.
... 50 Only one arc is observed in the EIS above room temperature; however, a new arc appears in the low-frequency region at low temperatures, resulting in two arcs, even for a single electrode. 28,[51][52][53][54][55][56] Thus, the Nyquist plot of a single electrode exhibits different characteristics from that of a Randles circuit. ...
... Figure 6a shows the EIS results of a lithium insertion electrode at state of charge (SOC) values of 50 and 0% (fully discharged states). 51 A low-frequency arc is observed at 50%, which disappears at 0%. Thus, the low-frequency arc is caused by the lithium insertion reaction. ...
... Here, the Rion in the linear region can be analyzed by measuring the EIS of the electrode in its initial state (SOC = 0%) (Fig. 6a). 51 By considering all the resistances related to the lithium insertion electrodes, an equivalentcircuit mode was obtained, as shown in Fig. 9a. 52 From the Nyquist plot, each resistance component was estimated as follows: ...
Electrochemical impedance spectroscopy (EIS) of lithium insertion electrodes is a powerful technique to facilitate the further development of lithium-ion batteries (LIBs) because it provides useful information on electrochemical reactions. However, EIS methodology using a three-electrode cell is yet to be established owing to the difficulty in designing the reference electrode configuration. Therefore, a symmetric-cell method has been proposed to measure the EIS of a single electrode in a two-electrode cell, and it has been actively applied to EIS measurements in recent years. EIS measurements using symmetric cells have resulted in several new discoveries and deepened our understanding of the EIS behavior of lithium insertion electrodes. In this review, we outline the progress of EIS measurements using the symmetric-cell method for lithium insertion electrodes. First, we explain the principle, fabrication method, and EIS analysis of symmetric cells. Subsequently, an equivalent-circuit model representing lithium insertion electrodes is proposed based on the EIS measurement results. Furthermore, the factors affecting the various resistances comprising the equivalent circuit, such as charge transfer, contact, and ionic transport resistances, are discussed, including the dependence of the resistances on the electrode thickness, porosity, and measurement temperature on the resistances. Finally, applications of the EIS of a single electrode obtained using symmetric cells are described, including the prediction of the EIS of LIB and acquisition of the EIS of a single electrode from that of full cells.
... To simplify the interpretation of the impedance data, the diameter of the "semi-circular" arc from the Nyquist plot was taken as the chargetransfer resistance (R ct ). 30 All the impedance spectra were normalized based on the area of the electrodes. ...
Extremely high nickel content positive electrode materials have high specific capacity leading to high energy density Li-ion cells. The long-term cycling stability of pouch cells with a single crystal LiNi0.95Mn0.04Co0.01O2 positive electrode material was studied here. Cells with such high nickel content demonstrated excellent cycling when only charged to 4.04 V (about 75% state of charge (SOC)), while they showed more capacity loss when charged to 4.18 V or 100% SOC. Lowering the upper cut-off voltage improves cycling stability but decreases the cell energy density. The main reason for the capacity loss at 40°C is due to positive electrode impedance growth, which originated from parasitic reactions between the positive electrode material and the electrolyte, especially when the cells are operated to 4.18 V. There was no positive electrode particle cracking and no significant active mass loss even for cells operated to 4.18 V. X-ray diffraction measurements of cycled positive electrodes indicated no appreciable amount of nickel migrating into the lithium layer, so the impedance growth mainly comes from the positive electrode surface. Using 1.2M LiPF6 fluoroethylene carbonate: ethyl methyl carbonate 20:80 electrolyte with 1 wt% lithium difluorophosphate allows cycle life to be extended by reducing impedance growth of the cell.
... EIS analysis that was performed at the end of the charge step indicates that the blocking electrode behavior transforms into a non-blocking electrode with the formation of a chargetransfer semi-circle at the intermediate frequency range and a Warburg diffusion tail at low frequencies (Fig. 5b). 10,67,68 The transition from blocking to non-blocking behavior is attributed to the lithiation of the carbon interlayer, where the activity of Li at the carbon/SE interface becomes non-zero. The Nyquist spectra were tted using an equivalent-circuit model as summarized in Table S2. ...
Carbon interlayers in anode-free SSBs form Li concentration gradients when charged at high current densities. Dynamic changes in the state-of-charge of the carbon interlayer influence the interfacial impedance and eventual nucleation of plated Li.
