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Lithium-Ion Battery Power Performance Assessment for the Climb Step of an Electric Vertical Takeoff and Landing (eVTOL) Application

  • Marm Dixit*
    Marm Dixit
    Electrification and Energy Infrastructures Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, United States
    *Email: [email protected]
    More by Marm Dixit
  • Anuj Bisht
    Anuj Bisht
    Electrification and Energy Infrastructures Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, United States
    More by Anuj Bisht
  • Rachid Essehli
    Rachid Essehli
    Electrification and Energy Infrastructures Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, United States
  • Ruhul Amin
    Ruhul Amin
    Electrification and Energy Infrastructures Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, United States
    More by Ruhul Amin
  • Chol-Bum M. Kweon
    Chol-Bum M. Kweon
    Army Research Directorate, Combat Capabilities Development Command Army Research Laboratory, Aberdeen Proving Ground, Maryland 21005, United States
  • , and 
  • Ilias Belharouak*
    Ilias Belharouak
    Electrification and Energy Infrastructures Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, United States
    *Email: [email protected]
Cite this: ACS Energy Lett. 2024, 9, 3, 934–940
Publication Date (Web):February 12, 2024
https://doi.org/10.1021/acsenergylett.3c02385

Copyright © 2024 The Authors. Published by American Chemical Society. This publication is licensed under

CC-BY-NC-ND 4.0.
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Abstract

High power is a critical requirement of lithium-ion batteries designed to satisfy the load profiles of advanced air mobility. Here, we simulate the initial takeoff step of electric vertical takeoff and landing (eVTOL) vehicles powered by a lithium-ion battery that is subjected to an intense 15C discharge pulse at the beginning of the discharge cycle followed by a subsequent low-rate discharge. We conducted extensive electrochemical testing to assess the long-term stability of a lithium-ion battery under these high-strain conditions. The main finding is that despite the performance recovery observed at low rates, the reapplication of high rates leads to drastic cell failure. While the results highlight the eVTOL battery longevity challenge, the findings also emphasize the need for tailored battery chemistry designs for eVTOL applications to address both anode plating and cathode instability. In addition, innovative second-use strategies would be paramount upon completion of the eVTOL services.

This publication is licensed under

CC-BY-NC-ND 4.0.
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One of the fundamental challenges in designing battery systems for electric vertical takeoff and landing (eVTOL) platforms lies in meeting the high-power demands during crucial flight maneuvers. (1) During several phases of its mission, the eVTOL application requires exceptionally high discharge rates from the onboard lithium-ion batteries (LiBs). (2) LiBs, under high-power discharge scenarios such that of an eVTOL, have not been explored enough because the current application spectrum in electric vehicles (EVs) and electronic devices does not require such a high power. (3,4) Understanding the implications of the high discharge pulses on the stability, performance, and longevity of LiBs is significant in assessing the suitability of the available battery chemistries.

The majority of studies of high-power lithium-ion batteries have focused on discharge rates ranging from 2C to 5C rates. (5−7) There is a significant body of literature delving into materials, processing, and cell configurations with the aim to improve the rate performance at the high discharge rates through both experimental as well as modeling approaches. (8−19) Further, most of the power studies only investigate discharge behaviors at high rates over the entire range of the depth of discharge of the battery. While these studies are extremely useful for electric vehicle applications, there is an increasing demand for more high-power-driven studies to assess the extremely fast charge and discharge needs for advanced air mobility applications. United States Advanced Battery Consortium (USABC) guidelines for testing batteries for EV applications indicate peak power testing at 5C discharge current for a pulse duration of 30 s. (20,21) Power requirements in eVTOL are strongly correlated to the type of the eVTOL aircraft and mission profile as well as the payload. Some of the key eVTOL designs are multirotor, tilt system, and lift and cruise (conventional). (1) These designs leverage different propulsion mechanisms to achieve the mission profile, rendering distinct power profile requirements in these systems. Typically, initial hover power required for takeoff is related directly to the effective disc loading in the eVTOL as given by the following equation: (22)

SPhover=1wbatgnhσ2ρair

Where, SPhover is the specific power for hover, wbat is the weight of the battery, g is the gravitational acceleration, ηh is the hover efficiency, σ is the disc loading of the eVTOL, and ρair is the air density. Depending on the type of eVTOL system, disc loading can range from 200 N/m2 all the way to 1000 N/m2. Correspondingly, the typical eVTOL designs require a power-to-energy ratio (effective discharge rates) ranging from 10C to 60C with peak power required both at the beginning of the discharge cycle (low depth of discharge) and end of discharge (high depth of discharge) as shown schematically in Figure 1A. In specific power terms, these values can potentially exceed 1000 kW/kg depending on the mass of the payload, mission profile, and aircraft design. (2,22,23)

Figure 1

Figure 1. High power requirements in eVTOL load profiles and electrochemical behavior of lithium-ion batteries under simulated takeoff step. (A) Schematic diagram showing major segments of an eVTOL mission profile and the corresponding power requirements. We are interested in evaluating the behavior of lithium-ion batteries within the initial high-power segment of takeoff. (B) Current profile for the testing carried out in this study. Cells are charged at a nominal 1C rate until a full state-of-charge is achieved (4.2 V cutoff). At the beginning of discharge, a current pulse equivalent to 15C is applied for 45 s. Subsequent discharge is carried out at a nominal C/3 current. For the batteries investigated here, 1C corresponds to ∼0.08 A, and 15C corresponds to roughly 1.2 A. (C) First charge–discharge cycle polarization curve with the dotted line showing the charge cycle and solid line depicting the discharge cycle. (D) Capacity retention of the cell over extended cycling under the simulated climb step discharge protocol. (E) Complete polarization curves and (F) zoomed in plot of the polarizations within the 15C discharge pulse segment for the 1st, 25th, 50th, 75th, and 100th cycles. The cut-off voltage of 3 V is identified by a dashed line in (E) and (F).

In recent years, significant research efforts have been directed toward enhancing the energy density, power output, and overall performance of LiBs. (24) However, the extreme power demands inherent to eVTOL operations necessitate a specialized investigation. Very limited experimental data sets exist in open literature investigating LiBs under these extreme power conditions. Recently, Vishwanathan reported a battery data set for eVTOL systems using commercial lithium- i on battery with an energy density of 230 Wh/kg, with a maximum discharge rate used for the climb and landing steps being roughly 7C for a pulse duration of 1 to 2 min. (25) Pushing the discharge rate pulse to higher values is crucial for harsher eVTOL applications; however, limited experimental validation of LiBs is available under these high strain conditions.

In this paper, we present a comprehensive analysis of the effects of high discharge pulses on LiBs, focusing specifically on the initial takeoff step of eVTOL operations. Through experimental studies, we explored the intricate interplay between power requirements, battery stability, and long-term performance. It is imperative to emphasize the intensity of the discharge pulse used in our eVTOL simulation in contrast with typical battery tests conducted for EV applications. In conventional EV testing scenarios, discharges are commonly performed at rates ranging from 1C to 3C, reflecting the vehicle’s normal driving conditions

These rates are significantly lower than those of the discharge pulse implemented in our study. The stark contrast underscores the specialized nature of our research tailored specifically to the exceptional power requirements of eVTOLs during their climb phase. The findings presented herein not only contribute to the eVTOL technology but also shed light on the broader applications of high-power LiBs in various fields. By simulating and analyzing the impact of these high discharge pulses, we aim to uncover valuable insights into the behavior of LiBs under such stressful conditions. This knowledge is pivotal for eVTOL manufacturers, battery researchers, and the broader electric vehicle industry, guiding the development of batteries that can withstand the demanding power requirements of eVTOLs and ensure stability and safety.

In the realm of eVTOL vehicles, the takeoff step presents a unique and intense challenge to the onboard energy storage system. This critical phase demands an extraordinary surge of power to propel the eVTOL vertically, thereby swiftly transitioning it from ground to air. To accurately replicate these extreme power demands, our study employs a high discharge pulse at a rate of 15 times the battery’s nominal capacity, denoted as 15C, for a duration of 45 s (Figures 1B and 2). This intense burst of power, required in the rapid climb of an eVTOL, serves as a crucial simulation parameter in our research. The choice of a 15C discharge pulse for 45 s is rooted in the need to replicate the average high-power demands by eVTOL batteries during the initial step. This rigorous simulation allows us to explore the battery’s response to extreme current drains, providing invaluable insights into its stability and overall performance under such challenging conditions. By subjecting the battery to a brief but intense burst of power, followed by a discharge at a more sustainable rate of C/3, which mirrors the eVTOL’s subsequent flight, we aim to dissect the intricate interplay between power surge, subsequent discharge, and their cumulative impact on the battery’s health.

Figure 2

Figure 2. Analysis of the cycling behavior under simulated initial step protocol. (A) Total discharge capacity across cycle numbers is plotted as a stacked bar chart to denote contributions from 15C and C/3 segment. (B) Evolution of average discharge voltage across cycle numbers plotted from 15C and C/3 segments individual. (C) Discharge capacity attained from individual 15C and C/3 segments. (D) Capacity ratio depicting the relative contribution from the 15C segment to the total discharge capacity of the cell.

The cycling performance of the cell subjected to this protocol is shown in Figure 2. The normalized capacity values can be referred to in the Supporting Information (Figure S2). The cell shows a consistent performance, delivering around 75 mAh capacity (175 mAh/g) with good retention for about 85 cycles after which the capacity of the pouch cell drops to 15 mAh(25 mAh/g) in the subsequent cycle (86th cycle). Looking at the polarization curves for these tests (Figure 2B and Figure S3), we observe that over the cycling period, the cell potential during the 15C discharge segment keeps dropping, while the cell potential during the C/3 segment is constant. Beyond 85 cycles, the cell polarizes toward the cutoff voltages within the 15C segment which significantly limits the capacity and restricts further discharges. At the point where the cell polarizes to the lower end cutoff voltage 3 V, we are not cycling significant amounts of lithium from the cathode (x in Li) and expect minimal lithium inventory loss (if any). The increasing polarization within the 15C segment could arise from chemical build-up at the cathode/anode interfaces (CEI/SEI) or could be primarily driven by the concentration gradient within the electrolyte and mass transport limitations within the electrodes. (26−31) We note that this behavior was observed in multiple cells, and no cell lasted for longer than 100 cycles under the above test conditions. We also note that in our study, all tests were conducted at an operating temperature of 30 °C. This deliberate choice aimed to maintain a consistent and controlled environment for our investigations, allowing us to focus on the specific aspects related to high-discharge pulses and their impact on battery stability. While our study primarily delves into the effects of rapid power demands on battery behavior, we recognize that temperature conditions play a crucial role in real-world eVTOL scenarios. Recent work by Mukherjee et al. emphasizes the pivotal role of both cell and ambient temperatures in determining achievable mission profiles and ensuring the safety of LiBs in various applications. (22) Further work to explore the interplay between temperature, high-power discharges, and the overall performance of LiBs in eVTOL applications is warranted.

To assess the performance of the two capacity segments individually, we carried out further analysis on the electrochemical data set (Figure 3). Capacity derived from individual segments is plotted against cycle number in Figure 3A,C, and Figure S1. Over the cycles in which the cell capacity is stable, we observed consistent capacity inputs from the 15C pulse as well as the C/3 segment. The 15C pulse delivered roughly 20% of the capacity of each cycle, while the C/3 segment delivered the rest (Figure 3D). However, for eVTOL applications, capacity retention alone does not provide adequate information regarding the performance of the cell. Achieving adequate power during the climb phase is pivotal for the mission profile to be achieved safely. In this regard, the evolution of the cell potential in individual cycles is also important to be evaluated. Average cell potential within the 15C and C/3 segments is plotted as a function of cycle number in Figure 3B. For the C/3 segment, the average cell potential is constant until cell failure due to huge polarization at around 3.5 V. For the 15C segment, we observed a continuously decreasing potential over the 80 cycles, consistent with the polarization growth observed in the discharge curves (Figure 2B). In 85 cycles, the average potential in the 15C segment drops from 3.5 to 3.3 V, a reduction of 200 mV. This drop was accompanied by a power drop from this segment by 7% within 80 cycles and a drastic drop after that due to increasing polarization. Following the intense 15C discharge pulse, the cell’s performance was further evaluated following a low-rate (C/3) cycling test (Figure 4). We carried out the test to assess if there was any fundamental material degradation that occurred during the 15C discharge segment. Remarkably, during this low-rate evaluation, the cell exhibited promising behavior, achieving its original capacity and showing good retention. This observation suggests that the capacity loss experienced after the 15C pulse test was not irreversible, and the cell’s electrochemical capabilities were partially restored under low-rate conditions. A key difference observed for the cell cycled after the high-rate pulse test was a discernible reduction in the average voltage during both charge and discharge processes (Figure 4C). During the charge step, we observe roughly a 100 mV drop in potential, while during discharge the potential drop is ∼50 mV. This drop suggests that the electrode interfaces possess a buildup of resistive layers that impact the energy and power yield of the cell.

Figure 3

Figure 3. Low-rate step investigation. (A) Charge and discharge capacity achieved from the cells subjected to the simulated climb step protocol under C/3–C/3 cycling. (B) Polarization curves of the cell under the low rate cycling protocol over 25 cycles. (C) Average charge and discharge potential of a pristine cell undergoing C/3–C/3 cycling compared to the average potential obtained in the low-rate investigation after cycling the cell under simulated climb step protocol.

Figure 4

Figure 4. Electrochemical behavior of lithium-ion batteries under simulated climb step after low-rate step. (A) Capacity retention of the cell over extended cycling under the simulated climb step discharge protocol. (B) Polarization curves of the cell for the 1st and the 5th cycle. The cut-off voltage of 3 V is identified by a dashed line in (B).

Despite the restoration of the original capacity, the decrease in average voltage highlighted a lingering effect of intense 15C pulse application. Understanding these subtle alterations is crucial in comprehensively assessing the long-term stability and resilience of LiBs in high- power eVTOL applications, providing valuable insights into future battery design and optimization efforts.

A high-rate pulse test was conducted after the low-rate recovery phase, revealing a striking vulnerability within the cell (Figure 4). Despite briefly regaining its initial capacity under low-rate conditions, the cell exhibited a clearly diminished resilience when subjected to the high-rate eVTOL-like strain. Shockingly, the cell failed within a mere 1–5 cycles reaching the polarization cutoff in the 15C pulse segment. Scanning electron microscope (SEM) analysis of the electrodes extracted from the pouch cells after cycling was carried out to assess the morphological and microstructural changes within the cell. Ex situ analysis of the electrodes shows clear evidence of residual plating on the anode, especially around the edge of the electrodes (Figure 5A,B). The elemental mapping is consistent with the SEI products anticipated from the breakdown of the XFC electrolyte (Figure S4). Further, the morphology of the deposits is consistent with Li plating. The origin of lithium plating on the anode is linked to the concentration of lithium ions in the vicinity of the graphite anode, electrode potential, and inherent transport properties of the electrolyte and anode. Typically, plating is observed during high-rate charging tests. The XFC electrolyte employed within this work was developed primarily to facilitate fast charge and eliminate plating due to higher conductivity as well as transference number. This electrolyte eliminates plating for charge rates up to 6C as shown previously. (31) This suggests that the degradation we observe here is linked directly to the cell testing configuration used in this study. The discharge pulse rates employed in this work are anticipated to drive significant concentration gradients in the electrolyte leading to depletion of ions at the electrode interface, driving local potentials to regions of lithium plating. These results indicate the need for a deeper investigation of the mechanism with advanced characterization techniques under operando conditions.

Figure 5

Figure 5. Post-mortem analysis of the cells. (A) Optical and (B) SEM images of the anode extracted from the cycled cells. (C) Optical and (D) SEM images of the cathode films after cycling.

The presence of lithium plating can lead to the formation of dendrites, needlelike structures that grow from the anode and can pierce the separator, causing short circuits and compromising the overall safety and lifespan of the battery. The detection of anode plating underscores the challenges associated with the rapid power surges typical of eVTOL operations. The extreme demands placed on the anode during high-rate discharges could trigger these plating phenomena, highlighting the need for advanced anode materials or innovative design approaches to mitigate this issue and enhance the battery’s cycling durability in eVTOL applications. In contrast, the intact cathode structure indicates its resilience against the high-power stresses experienced during eVTOL-like discharges (Figure 5C,D). The preserved integrity of the cathode material suggests that, even under intense high-rate discharges, the cathode’s structural stability and electrochemical activity remain relatively unaffected. The absence of transition metal dissolution within the span of our test conditions was also observed with energy dispersive spectroscopy (EDS) indicating a stable cathode. Also, we do not observe any structural changes in the cycled electrodes compared to the pristine electrode (Figure S5).

These results emphasize a crucial aspect: LiBs utilized in eVTOL applications might not demonstrate prolonged cycle life, especially when subjected to the rapid and intense power demands emblematic of vertical ascents. However, the fact that the cell’s low-rate performance remained unaffected suggests that these batteries, despite their diminished high-rate capabilities, might find a second life in applications where low-rate power delivery is sufficient. Repurposing these batteries for applications that do not demand rapid power surges could significantly extend their usability and minimize waste. It is crucial to note, however, that repurposing cells for different applications involves inherent complexities that necessitate careful consideration. Several factors, such as Battery Management System (BMS) compatibility, system repurposing, and overall electronic integration must be thoroughly examined. Reconfiguring LiBs for alternative uses requires a multifaceted approach, addressing challenges at various levels, from individual cell characteristics to pack-level considerations, and electronic interfaces. This finding emphasizes the importance of exploring alternative applications for these batteries after their eVTOL service life or the use for a hybrid-electric propulsion system, providing a sustainable approach to managing their lifecycle and contributing to the broader goal of reducing environmental impact in the realm of electric mobility. These results serve as a crucial reminder of the nuanced balance between eVTOL power requirements, battery lifespan, and the potential for repurposing, offering valuable insights for the sustainable integration of energy storage systems in future advanced air mobility endeavors.

In conclusion, our comprehensive study sheds light on the intricate dynamics between high discharge pulses and LiBs in eVTOL applications. The discharge rate of the 15C pulse was employed at the beginning of the discharge cycle to imitate the initial takeoff step of an eVTOL load profile. The results showed that LiBs cannot sustain high discharge rate pulses for extended cycling, even though the low-rate capabilities are not impacted. The observed rapid failure upon reapplication of high-rate strains accentuates the challenges in extending the eVTOL battery lifecycle. Repurposing these batteries for low-rate applications presents a sustainable solution, aligning with environmental goals or they can be used for hybrid-electric propulsion systems where the discharge rates can be optimized not to deteriorate the battery materials. This research not only advances our understanding of eVTOL battery performance but also guides future developments in battery technology, emphasizing the imperative balance between high-power requirements, structural stability, and sustainable second-use strategies in the evolving landscape of advanced air mobility.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsenergylett.3c02385.

  • Detailed experimental methods; electrochemical performance of the pouch cells plotted as absolute and mass normalized capacities; EDS maps of the cycled anode; XRD patterns of the pristine and the cycled anode and cathode films (PDF)

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  • Corresponding Authors
  • Authors
    • Anuj Bisht - Electrification and Energy Infrastructures Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, United States
    • Rachid Essehli - Electrification and Energy Infrastructures Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, United States
    • Ruhul Amin - Electrification and Energy Infrastructures Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, United StatesOrcidhttps://orcid.org/0000-0002-0054-3510
    • Chol-Bum M. Kweon - Army Research Directorate, Combat Capabilities Development Command Army Research Laboratory, Aberdeen Proving Ground, Maryland 21005, United States
  • Notes
    The authors declare no competing financial interest.

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This article has been authored by UT-Battelle, LLC, under Contract DE-AC0500OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for the United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan). This research at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the US Department of Energy under contract DE-AC05- 00OR22725, was sponsored by the US Army DEVCOM Army Research Laboratory and was accomplished under Support Agreement 2371-Z469-22. XRD is conducted as part of a user project at the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory. We thank Dr. Jong Keum for his help. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the DEVCOM Army Research Laboratory or the U.S. Government.

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    Li, M.; Feng, M.; Luo, D.; Chen, Z. Fast Charging Li-Ion Batteries for a New Era of Electric Vehicles. Cell Reports Physical Science 2020, 1 (10), 100212,  DOI: 10.1016/j.xcrp.2020.100212
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    Du, Z.; Yang, Z.; Tao, R.; Shipitsyn, V.; Wu, X.; Robertson, D. C.; Livingston, K. M.; Hagler, S.; Kwon, J.; Ma, L. A Novel High-Performance Electrolyte for Extreme Fast Charging in Pilot Scale Lithium-Ion Pouch Cells. Batteries & Supercaps 2023, 6 (10), e202300292  DOI: 10.1002/batt.202300292
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    Badwekar, K.; Dingari, N. N.; Mynam, M.; Rai, B. Role of lithium salt in reducing the internal heating of a lithium ion battery during fast charging. J. Appl. Electrochem. 2022, 52 (6), 941951,  DOI: 10.1007/s10800-022-01681-2

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  • Abstract

    Figure 1

    Figure 1. High power requirements in eVTOL load profiles and electrochemical behavior of lithium-ion batteries under simulated takeoff step. (A) Schematic diagram showing major segments of an eVTOL mission profile and the corresponding power requirements. We are interested in evaluating the behavior of lithium-ion batteries within the initial high-power segment of takeoff. (B) Current profile for the testing carried out in this study. Cells are charged at a nominal 1C rate until a full state-of-charge is achieved (4.2 V cutoff). At the beginning of discharge, a current pulse equivalent to 15C is applied for 45 s. Subsequent discharge is carried out at a nominal C/3 current. For the batteries investigated here, 1C corresponds to ∼0.08 A, and 15C corresponds to roughly 1.2 A. (C) First charge–discharge cycle polarization curve with the dotted line showing the charge cycle and solid line depicting the discharge cycle. (D) Capacity retention of the cell over extended cycling under the simulated climb step discharge protocol. (E) Complete polarization curves and (F) zoomed in plot of the polarizations within the 15C discharge pulse segment for the 1st, 25th, 50th, 75th, and 100th cycles. The cut-off voltage of 3 V is identified by a dashed line in (E) and (F).

    Figure 2

    Figure 2. Analysis of the cycling behavior under simulated initial step protocol. (A) Total discharge capacity across cycle numbers is plotted as a stacked bar chart to denote contributions from 15C and C/3 segment. (B) Evolution of average discharge voltage across cycle numbers plotted from 15C and C/3 segments individual. (C) Discharge capacity attained from individual 15C and C/3 segments. (D) Capacity ratio depicting the relative contribution from the 15C segment to the total discharge capacity of the cell.

    Figure 3

    Figure 3. Low-rate step investigation. (A) Charge and discharge capacity achieved from the cells subjected to the simulated climb step protocol under C/3–C/3 cycling. (B) Polarization curves of the cell under the low rate cycling protocol over 25 cycles. (C) Average charge and discharge potential of a pristine cell undergoing C/3–C/3 cycling compared to the average potential obtained in the low-rate investigation after cycling the cell under simulated climb step protocol.

    Figure 4

    Figure 4. Electrochemical behavior of lithium-ion batteries under simulated climb step after low-rate step. (A) Capacity retention of the cell over extended cycling under the simulated climb step discharge protocol. (B) Polarization curves of the cell for the 1st and the 5th cycle. The cut-off voltage of 3 V is identified by a dashed line in (B).

    Figure 5

    Figure 5. Post-mortem analysis of the cells. (A) Optical and (B) SEM images of the anode extracted from the cycled cells. (C) Optical and (D) SEM images of the cathode films after cycling.

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    • Detailed experimental methods; electrochemical performance of the pouch cells plotted as absolute and mass normalized capacities; EDS maps of the cycled anode; XRD patterns of the pristine and the cycled anode and cathode films (PDF)


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