Impedance Rise Research Articles

Anchoring Interfacial Nickel Cations on Single-Crystal LiNi0.8Co0.1Mn0.1O2 Cathode Surface via Controllable Electron Transfer

Severe Ni dissolution and the resulted surface impedance rise for single crystal LiNi0.8Co0.1Mn0.1O2 surface during electrochemical cycles is the main challenge greatly hindering its industrial app...

673Bipolar radiofrequency ablation supported by non-ionic catheter irrigation

Abstract Introduction Bipolar radiofrequency catheter ablation (Bi-RFCA) or irrigation of ablation catheter (AC) using non-ionic coolant, such as dextrose-5 in water (D5W), are novel ways to improve lesion formation in case of arrhythmia refractoriness. Combination of these two methods has not yet been described. Puprose To determine feasibility and effectiveness of Bi-RFCA additionally supported by non-ionic catheter irrigation for treatment of refractory premature ventricular complexes (PVC) or ventricular tachycardia (VT). Methods Consecutive patients after failed extensive Bi-RFCA or D5W-irrigated ablation for symptomatic PVCs or non-sustained VT (nsVT) underwent Bi-RFCA supported with D5W coolant. Results We ultimately enrolled 2 patients (2 males, age 64 ± 12 years) after failed extensive ablations for the left ventricular summit PVCs and nsVT to undergo Bi-RFCA supported with D5W irrigation of both AC and intracardiac return electrode (IRE). Previous pharmacological antiarrhythmic treatment consisting of at least one drug and catheter ablation failed in both patients. Bi-RFCA was delivered between earliest activation sites located in the left/right aortic commissure and the left pulmonic cusp (Figure). Efforts were made to achieve safe distance from coronary arteries, AC, and IRE. Bipolar RFCA (35 ± 7W power, 8 ± 4 applications, 199 ± 166s RF time) led to acute elimination of PVCs in both patients. Baseline impedance oscillated around 250Ω and initial 50-70Ω impedance drop was observed during first 20s of bipolar applications, followed by impedance rise up to 350-450Ω. No steam pop occurred and there were no complications during procedures. All antiarrhythmic drugs were discontinued. Follow-up lasted 8 ± 2 months, there was no nsVT recurrence and 90,4% PVC burden reduction was achieved: from 30000 to 3100 PVC/day in patient #1 and from 39000 to 3500 PVC/day in patient #2. Both patients remained symptom-free. Conclusion Bi-RFCA can be additionally supported using non-ionic D5W coolant. Such approach is feasible and can be safe and effective. More data on impedance imbalance during D5W-supported bipolar RF applications is warranted. Abstract Figure. Fluoroscopic view and 12-lead ECG

Improvement of cycling stability and high-temperature performance of Li[Ni0.80Co0.15Al0.05]O2 cathode by thin-layer AlF3 coating

Li[Ni0.80Co0.15Al0.05]O2 is considered as a promising cathode material due to its high specific capacity. Nevertheless, the irreversible formation of electrochemically inactive NiO phase on the surface of the particles would significantly deduce impedance rise and power decrease during cycling. Herein, a thin-layer AlF3-coated Li[Ni0.80Co0.15Al0.05]O2 has been synthesized via a facile solution method, and the optimized coating content has been confirmed. Compared with the pristine sample, the 0.5% AlF3−coated Li[Ni0.80Co0.15Al0.05]O2 composite exhibits significantly improved cycling stability and high-temperature performance. The improved electrochemical properties can be attributed to that the thin AlF3 layer can stabilize the surface structure of active material and a LiAlO2 phase with high ionic conductivity is formed on the surface of the particles during cycling.

Emerging Potassium Metal Anodes: Perspectives on Control of the Electrochemical Interfaces.

ConspectusPotassium metal serves as the anode in emerging potassium metal batteries (KMBs). It also serves as the counter electrode for potassium ion battery (KIB) half-cells, with its reliable performance being critical for assessing the working electrode material. This first-of-its-kind critical Account focuses on the dual challenge of controlling the potassium metal-substrate and the potassium metal-electrolyte interface so as to prevent dendrites. The discussion begins with a comparison of the physical and chemical properties of K metal anodes versus the much oft studied Li and Na metal anodes. Based on established descriptions for root causes of dendrites, the problem should be less severe for K than for Li or Na, while in fact the opposite is observed. The key reason that the K metal surface rapidly becomes dendritic in common electrolytes is its unstable solid electrolyte interphase (SEI). An unstable SEI layer is defined as being non-self-passivating. No SEI is perfectly stable during cycling, and all SEI structures are heterogeneous both vertically and horizontally relative to the electrolyte interface. The difference between a "stable" and an "unstable" SEI may be viewed as the relative degree to which during cycling it thickens and becomes further heterogeneous. The unstable SEI on K metal leads to a number of interrelated problems, such as low cycling Coulombic efficiency (CE), a severe impedance rise, large overpotentials, and possibly electrical shorting, all of which have been reported to occur as early as in the first 10 plating/stripping cycles. Many of the traditional "interface fixes" employed for Li and Na metal anodes, such as various artificial SEIs, surface membranes, barrier layers, secondary separators, etc., have not been attempted or optimized for the case of K. This is an important area for further exploration, with an understanding that success may come harder with K than with Li due to K-based SEI reactivity with both ether and ester solvents.The second critical problem with K metal anodes is that they do not thermally or electrochemically wet a standard (untreated) Cu foil current collector. Published experimental and modeling research directly highlights the weak bonding between the K atoms and a Cu surface. Existing surface treatment approaches that achieve improved K wetting are discussed, along with the general design rules for future studies. Also discussed are geometry-based methods to tune nucleation as well dual approaches where nucleation and SEI structure are tuned through complementary schemes to achieve extended half-cell and full battery stability. We hypothesize that K metal never achieves a planar wetting morphology even at cycle one, making the dendrites "baked-in". We propose that classical thin film growth models, Frank van der Merwe (F-M), Volmer-Weber (V-W), and Stranski-Krastanov (S-K), can be employed to describe early stage plating behavior. It is demonstrated that islandlike V-W growth is the applicable description for the natural plating behavior of K on pristine Cu. Moving forward, there are three inter-related thrusts to be pursued: First, K salt-based electrolyte formulations have to mature and become further tailored to handle the increased reactivity of a metal rather than an ion anode. Second, the K-based SEI structure needs to be further understood and ultimately tuned to be less reactive. Third, the energetics of the K metal-current collector interface must be controlled to promote planar wetting/dewetting throughout cycling.

Origins of Capacity Fade and Material Degradation in Ni-Rich NMC Li-Ion Batteries

Nickel-rich layered oxide cathode materials are promising candidates for automotive lithium-ion batteries due to their low cost and high reversible capacity.1 However, paired with graphite anodes these materials exhibit faster voltage and capacity fading compared to isostructural LiNixMnyCozO2 (NMC) cathodes with lower nickel content.2 In this work we will explore the origins of capacity fade and material degradation in graphite/LiNi0.8Mn0.1Co0.1O2 (NMC811) full cells. With a focus on strategically designed electrochemical protocols (see Fig. 1), the role of several key cycling parameters (e.g. upper cut-off voltage, time at high voltage, phase transitions) on the degradation are decoupled. The ageing processes are quantified in terms of the full cell capacity retention, impedance rise, electrode slippage, and NMC cathode deterioration. We find that most full cell capacity loss and impedance rise is caused by increasing the upper cut-off voltage to >4.2 V, with the impedance increase largely driven by concomitant full state-of-charge (SOC) cycling. Time spent at high voltage (voltage holds) has less impact on these parameters. These findings are supported by electron microscopy and spectroscopy experiments (SEM, high-resolution TEM, and STEM-EELS) on cycled electrodes, which show clear evidence for cycle history dependent degradation including particle cracking, shearing, and surface reconstruction.

Analysis of the Impact of Fast Charging on Aging for Smartphone Cells: A Case Study Using Synchrotron Based Techniques

With the rapid market increase of consumer electronic devices such as smartphones and tablets, the performance of lithium-ion batteries in such devices becomes an important factor. In particular, fast charging, longer lasting batteries and safety are primary concerns for consumers. Lithium cobalt oxide (LCO) is a common cathode material for these applications, and in smartphone applications with 1-2 cycles a day, LCO has been proven to be a good cathode with its high cycle life.1,2 However, besides offering high cycling stability and power density for mobile consumer applications, another requirement for LIBs utilized in smartphones and other portable electronic devices is the capability of fast charging, without a detrimental impact on the cycling stability. Different fast charging profiles can lead to various extents of degradation within the full cell. Consequently, strategies are needed to avoid or mitigate any negative impact of fast charging on battery capacity, power degradation and cycle life.In this work, we employed extensive synchrotron-based characterization methods on smartphone batteries (LCO/graphite), offering new insight into the various degradation mechanisms during fast charging. Specifically we focus on an in-house developed fast-charging profile based on a physics-based battery model and compare it with the fast charging profile provided by the OEM. We reveal how lithium plating occurring on the anode side during fast charging is ‘mirrored’ on the cathode side leading to inactive cathode areas that only participate partly in lithium intercalation. While no morphological changes were observed in the cathode opposing the plating sides on the anode, in-situ hard XAS spectroscopy shows that deactivated spots on the cathode are not as redox active anymore, and synchrotron micro XRD shows significant changes in the lattice d-spacing value. Further, we use micro XRF to map the Co content in different regions of the anode, which stems from cathode transition metal dissolution. Finally, we conclude that a fast charging strategy derived from a physics-based model drastically reduces capacity fade and rate of impedance rise in a LCO/graphite smartphone cell as used in this work. References 1 L. Wang, J. Ma, C. Wang, X. Yu, R. Liu, F. Jiang, X. Sun, A. Du, X. Zhou and G. Cui, Adv. Sci., 2019, 6, 1900355.2 M. S. Whittingham, Chem. Rev., 2004, 104, 4271–4302.

The Synergetic Effect of LiMg0.5Mn1.5O4 Coating and Mg2+ Doping on Improving Electrochemical Performances of High‐Voltage LiNi0.5Mn1.5O4 by Sol‐Gel Self‐Combustion Method

AbstractThe composites of LiNi0.5Mn1.5O4 (LNMO) modified with LiMg0.5Mn1.5O4 (LMgMO) named LNMO@LMgMO as cathode materials for lithium ion battery that can withstand high voltage and high temperature were prepared by a sol‐gel self‐combustion method. The results of physical characterization show that the LMgMO layer was effectively coated on the surface of LNMO, and the Mg2+ was also doped into the lattice of LNMO. Electrochemical tests reveal that the LNMO@LMgMO composites deliver excellent electrochemical performance, especially for LNMO@LMgMO‐1%, including great capacity retention (91.4% for 500 cycles at 25 °C and 90.4% for 100 cycles at 55 °C at 2 C in the 3.5‐5.2 V) and superior rate capability (95.6 mAh g−1 under 10 C). Moreover, the synergetic effect of LMgMO coating and Mg2+ doping could alleviate the impedance rise.

Inhomogeneous Temperature Distribution Affecting the Cyclic Aging of Li-Ion Cells. Part II: Analysis and Correlation

Temperature has a significant influence on the behavior of batteries and their lifetime. There are several studies in literature that investigate the aging behavior under electrical load, but are limited to homogeneous, constant temperatures. This article presents an approach to quantifying cyclic aging of lithium-ion cells that takes into account complex thermal boundary conditions. It not only considers different temperature levels but also spatial and transient temperature gradients that can occur despite-or even due to-the use of thermal management systems. Capacity fade and impedance rise are used as measured quantities for degradation and correlated with the temperature boundary conditions during the aging process. The concept and definition of an equivalent aging temperature (EAT) is introduced to relate the degradation caused by spatial and temporal temperature inhomogeneities to similar degradation caused by a homogeneous steady temperature during electrical cycling. The results show an increased degradation at both lower and higher temperatures, which can be very well described by two superimposed exponential functions. These correlations also apply to cells that are cycled under the influence of spatial temperature gradients, both steady and transient. Only cells that are exposed to transient, but spatially homogeneous temperature conditions show a significantly different aging behavior. The concluding result is a correlation between temperature and aging rate, which is expressed as degradation per equivalent full cycle (EFC). This enables both temperature-dependent modeling of the aging behavior and its prediction.

Fabrication of Ti3C2 MXene Microelectrode Arrays for In Vivo Neural Recording.

Implantable microelectrode technologies have been widely used to elucidate neural dynamics at the microscale to gain a deeper understanding of the neural underpinnings of brain disease and injury. As electrodes are miniaturized to the scale of individual cells, a corresponding rise in the interface impedance limits the quality of recorded signals. Additionally, conventional electrode materials are stiff, resulting in a significant mechanical mismatch between the electrode and the surrounding brain tissue, which elicits an inflammatory response that eventually leads to a degradation of the device performance. To address these challenges, we have developed a process to fabricate flexible microelectrodes based on Ti3C2 MXene, a recently discovered nanomaterial that possesses remarkably high volumetric capacitance, electrical conductivity, surface functionality, and processability in aqueous dispersions. Flexible arrays of Ti3C2 MXene microelectrodes have remarkably low impedance due to the high conductivity and high specific surface area of the Ti3C2 MXene films, and they have proven to be exquisitely sensitive for recording neuronal activity. In this protocol, we describe a novel method for micropatterning Ti3C2 MXene into microelectrode arrays on flexible polymeric substrates and outline their use for in vivo micro-electrocorticography recording. This method can easily be extended to create MXene electrode arrays of arbitrary size or geometry for a range of other applications in bioelectronics and it can also be adapted for use with other conductive inks besides Ti3C2 MXene. This protocol enables simple and scalable fabrication of microelectrodes from solution-based conductive inks, and specifically allows harnessing the unique properties of hydrophilic Ti3C2 MXene to overcome many of the barriers that have long hindered the widespread adoption of carbon-based nanomaterials for high-fidelity neural microelectrodes.

Electric Vehicle Battery Performance Investigation Based on Real World Current Harmonics

Electric vehicle (EV) powertrains consist of power electronic components as well as electric machines to manage the energy flow between different powertrain subsystems and to deliver the necessary torque and power requirements at the wheels. These power subsystems can generate undesired electrical harmonics on the direct current (DC) bus of the powertrain. This may lead to the on-board battery being subjected to DC current superposed with undesirable high- and low- frequency current oscillations, known as ripples. From real-world measurements, significant current harmonics perturbations within the range of 50 Hz to 4 kHz have been observed on the high voltage DC bus of the EV. In the limited literature, investigations into the impact of these harmonics on the degradation of battery systems have been conducted. In these studies, the battery systems were supplied by superposed current signals i.e., DC superposed by a single frequency alternating current (AC). None of these studies considered applying the entire spectrum of the ripple current measured in the real-world scenario, which is focused on in this research. The preliminary results indicate that there is no difference concerning capacity fade or impedance rise between the cells subjected to just DC current and those subjected additionally to a superposed AC ripple current.

Rate-Dependent Aging Resulting from Fast Charging of Li-Ion Cells

The mass electrification of personal and service vehicles is reliant on the ability of battery packs to undergo extreme fast recharging. A central challenge is that the repeated exposure to high currents can trigger and/or accelerate mechanisms of performance degradation, such as lithium deposition, mechanical damage of active material particles, and impedance rise. Here, we investigate whether constraining high-rate charging to limited state-of-charge (SOC) ranges can mitigate these aging processes. Our experiments map the boundaries of lithium plating conditions, and also indicate that permanent losses of electrode capacity appear to be a function of cycle number, but not charging rate. Interestingly, we show that impedance rise appears to depend on charging rate alone, and not on the amount of charge passed at each cycle. This observation suggests that limiting fast charging to a narrow SOC range would only delay cell aging, but not fully prevent it from happening. We identify oxide-particle cracking as the likely mechanism for this impedance rise, suggesting that particle and electrode design are essential to enable fast charging. The findings of this work can inform the development of fast-charging protocols that are less damaging to cell health.

Revealing Grain-Boundary-Induced Degradation Mechanisms in Li-Rich Cathode Materials.

Despite their high energy densities, Li- and Mn-rich, layered-layered, xLi2MnO3·(1 - x)LiTMO2 (TM = Ni, Mn, Co) (LMR-NMC) cathodes require further development in order to overcome issues related to bulk and surface instabilities such as Mn dissolution, impedance rise, and voltage fade. One promising strategy to modify LMR-NMC properties has been the incorporation of spinel-type, local domains to create "layered-layered-spinel" cathodes. However, precise control of local structure and composition, as well as subsequent characterization of such materials, is challenging and elucidating structure-property relationships is not trivial. Therefore, detailed studies of atomic structures within these materials are still critical to their development. Herein, aberration corrected-scanning transmission electron microscopy (AC-STEM) is utilized to study atomic structures, prior to and subsequent to electrochemical cycling, of LMR-NMC materials having integrated spinel-type components. The results demonstrate that strained grain boundaries with various atomic configurations, including spinel-type structures, can exist. These high energy boundaries appear to induce cracking and promote dissolution of Mn by increasing the contact surface area to electrolyte as well as migration of Ni during cycling, thereby accelerating performance degradation. These results present insights into the important role that local structures can play in the macroscopic degradation of the cathode structures and reiterate the complexity of how synthesis and composition affect structure-electrochemical property relationships of advanced cathode designs.

Performance of the Durata implantable cardioverter defibrillator lead: results of an independent multicenter study.

The high rate of implantable cardioverter defibrillator (ICD) lead failures related to the Sprint Fidelis' and Riata's design have raised serious concerns about the reliability of ICD leads. The St. Jude Medical Durata family of leads replaced the preceding Riata line following increased rates of lead failure (1.17% per year). The aim of our study was to evaluate the long-term performance of the Durata lead. Eight hundred and eighteen Durata ICD leads were implanted in 11 Italian centers. The incidence of lead failure, defined as a sudden rise in long-term pacing or defibrillation impedance and/or a sudden change in R-wave amplitude and capture thresholds, was assessed. The incidences of lead dislodgment and lead perforation were also evaluated. During a median follow-up of 1353 days (3.7 years; 25-75th interquartile range 806-1887 days) lead failure occurred in 16/818 leads (0.54%/year). The overall survival, free of lead failure, was 98.9% at 3 years, 98.2% at 4 years and 97.5% at 5 years. Lead dislodgment occurred in 12/818 leads with an incidence of 0.4%/year. No cases of cardiac perforation were reported. No major adverse events were reported except for two cases of inappropriate shocks as a consequence of failure or dislodgment. Our study suggests that the Durata lead does not engender a higher risk of failure. Overall survival, free from lead failure, was found to be higher than previously reported for the Riata lead.

Optimization and characterization of a novel internally-cooled radiofrequency ablation system with optimized pulsing algorithm in an ex-vivo bovine liver

Purpose: To prospectively characterize and optimize radiofrequency energy deposition to determine ideal parameters for achieving large ablation zones.Materials and methods: An internally-cooled RF system was used to perform 214 ablations in 72 ex-vivo bovine livers. Tip exposure (1–5 cm), electrode current (400–2500 mA), and application duration (3–15 min) were systematically varied. A pulsing algorithm optimized efficiency of RF deposition, including initial automatic ramping followed by adjustment in current, in response to changes in tissue impedance. Following the procedure ablation diameter and length were measured, sphericity calculated, and correlated with parameters of energy deposition and tissue temperatures.Results: Increasing electrode exposure from 1–5 cm produced linear increases in ablation diameter from 1.4 ± 0.1 to 5.3 ± 0.1 cm (y = 1.1x–0.5; R2 = 0.93), and length (y = 1.18x + 0.34; R2 = 0.92). A sphericity index >0.85 was noted at optimal energy setting for electrode exposures of 1–4 cm. Maximum temperatures post-ablation increased with active tip length from 68.5 ± 4.9 °C to 91.3 ± 1.5 °C in a logarithmic (y = 0.94ln(x)−2.75; R2 = 0.90) or power relationship between temperature and the resultant ablation diameter (y = 0.27e0.0295x; R2 = 0.76). A tight exponential relationship (y = 0.28x0.38; R2 = 0.97) was also observed between total energy deposition and ablation diameter. Finally, a multifactor relationship of the diameter of ablation to electrode tip exposure and the time to first impedance rise was successfully modeled, with a root mean squared error of 1.9 mm and R2 = 0.95.Conclusion: Large, reproducible, and spherical ablation areas can be achieved with the novel system described, with efficient delivery of RF energy deposited into tissue. These findings may have important clinical relevance in regards to the clinical utility of RF ablation compared to other competitive forms of thermal tumor ablation.

Structural underpinnings of cathode protection by in situ generated lithium oxyfluorophosphates

The in situ strategy of cathode protection opportunistically uses PF6− anions in electrolyte as chemical reagents to convert inactive precursor molecules to active electrolyte additives. With our approach, a bifunctional x(SiMe3)2 precursor replaces fluoride in the hexafluorophosphate, forming either a bidentate monoanion P(x)F4− or a linear x(PF5−)2 dianion, depending on the bridge x (e.g., oxalato, malonato, succinato, and catecholato). While the efficiency of these species as cathode protective agents has been demonstrated, the mechanism for their beneficial action remains unknown. In this study, several molecular precursors have been synthesized, and the topology and energetics of secondary anions were correlated with their cycling performance. Regardless of their structural motif, all such additives demonstrated improved electrochemical performance by reducing initial cathode impedance and lowering the rate of capacity fade compared to the baseline electrolyte. However, bidentate monoanions with a malonato bridge showed significant advantage over other molecular designs for mitigating the impedance rise, suggesting that structural strain in the anion is important for easing surface modification of the cathode.

New Electrolyte Additives Formed By in Situ Method for High Voltage Lithium Ion Battery

Developing high-voltage Li ion batteries (LIBs) is an important trend to fit high energy and power density requirement of electric vehicles and hybrid electric vehicles. This requires the cathode materials and concomitant electrolyte to accommodate the high voltage working condition. However, continually exposed to high voltage, the cathode materials could gradually deteriorate and eventually cause the failure of battery. To address this issue, electrolyte additives can be an economic solution based on current existing electrolyte system, since it can decompose on the electrodes forming thin protective layer during formation cycles to prevent further deleterious reactions. The nominal electrolyte additives here are the precursors, which can spontaneously react with electrolyte when introduced into the electrolyte to yield the target surface-modifying products that can effectively protect the cathode. These additives were proved exceptional, since they delay both the impedance rise and capacity fade in the LIBs. To extend the library of this type of additives and explore more effective additives, we applied the molecular engineering to tune molecular backbone, functionality and substitution to obtain different surface-modifying products and maximize the battery performance. In addition, the in situ method is particularly beneficial to scale up electrolyte preparation, since it doesn’t need any post separation and purification process. By varying the structure of the additive precursor, we clearly see a trend that is governed by thermodynamics which determine the product configuration. The electrochemistry of these additives and their application in composite cathodes will be also discussed. Our strategy of synthesizing new electrolyte additives by in situ method will open up and facilitate the development of the lithium ion batteries toward high energy and high power density.

Rate and Voltage Dependence of the Electrode-Electrolyte Interface in Ni Containing Lithium-Ion Cathode Materials

Performance, safety, lifetime, and cost of lithium-ion batteries (LIB) are strongly influenced by the active materials used. As a result, cell chemistries are selected with the end goal in mind. For applications requiring superior power and safety, cells containing LiFePO4 cathodes and graphite anodes with an organic liquid electrolyte are frequently used. The major drawback of LIB cells designed for high-power is a relatively low energy density compared to high-energy cells, which conversely have poor rate capability. While graphite anodes remain a constant in most commercial LIB, recent research has identified cathode materials which would potentially mitigate the tradeoff between power, energy, and safety. In particular, spinel structured “LNMO” (LiNi0.5Mn1.5O4) and layered nickel-rich “NCM” compounds (LiNixMnyCozO2, X ≥ 0.5) have reportedly high energy densities relative to LiFePO4 while maintaining good power capability and thermal stability (1) (2). While LNMO and NCM compounds have similar composition and produce Ni4+ when fully charged, several reports have highlighted variations in surface chemistry resulting from electrolyte-electrode interactions as a function of cathode stoichiometry (3; 4; 5). One issue known to influence the surface chemistry and associated cycling stability of transition metal oxide cathode materials is the upper voltage cutoff needed to extract lithium during charge. Layered compounds can typically be reversibly delithiated within a voltage range of 4.2 to 4.6 V vs. Li/Li+ depending on the specific stoichiometry, while the spinel must be charged in excess of 4.8 V vs. Li/Li+, which historically has been a major hurdle to application. These upper voltage cutoff are already within the range of expected electrolyte oxidation, which is exacerbated by over potentials produced when charging at high current densities which further increase the upper voltage cutoff required to fully delithiate the cathode. This presentation will focus on analysis of the electrode-electrolyte interface, which is known to be a critical indicator of cell safety and lifetime, as a function of high-rate cycling and upper voltage cutoff. Composite cathodes containing spinel LNMO and layered NCM523 were cycled in a conventional lithium-ion electrolyte at various rates of charge and discharge, then disassembled in an inert atmosphere for analysis by X-ray Photoelectron Spectroscopy (XPS). Capacity and electrochemical impedance measurements were correlated with XPS analysis. Our results indicated that even when cycled in identical electrolytes spinel and layered compounds have notably different responses to an increased charge rate, specifically high rate charging (5C rate) is actually found to benefit LNMO, leading to lower impedance rise and associated formation of LiF, while the opposite is true for NCM523. One complicating factor in the XPS analysis of composite electrode is the presence of inactive components, specifically the binder and conductive additive. Both of these compounds dilute the overall signal detected from the active material, and some reports suggest may even contribute to the specific surface chemistry observed. To remove these effects, sol-gel films of identical composition to the composite electrode active materials were also synthesized and subjected to electrochemical cycling in the same electrolyte. [1] Review-Li-Rich Layered Oxide Cathodes for Next-Generation Li-Ion Batteries: Chances and Challenges. Rozier, P and Tarascon, JM. 14, 2015, Journal of the Electrochemical Society, Vol. 162, pp. A2490-A2499. [2] Spinel LiNi0.5Mn1.5O4 and its derivates as cathodes for high-voltage Li-ion batteries. Liu, G Q, Wen, L and Liu, Y M. 2010, Journal of Solid State Electrochemistry, Vol. 14, pp. 2191-2202. [3] Coupled LiPF6 Decomposition and Carbonate Dehydrogenation Enhanced by Highly Covalent Metal Oxides in High-Energy Li-Ion Batteries. Yu, Y, et al. 2018, Journal of Physical Chemistry C, Vol. 122, pp. 27368-27382. [4] XPS Studies of Surface Chemistry Changes of LiNi0.5Mn0.5O2 Electrodes during High-Voltage Cycling. Quinlan, RA, et al. 4, 2013, Journal of the Electrochemical Society, Vol. 160, pp. A669-A677. [5] Probing the Electrode-Electrolyte Interface in Cycled LiNi0.5Mn1.5O4 by XPS Using Mg and Synchrotron X-rays. Mansour, AN, et al. 14, 2016, Journal of the Electrochemical Society, Vol. 163, pp. A2911-A2918.

Effect of Fast-Charging on Ageing of Energy-Optimized Automotive LiNi1/3Mn1/3Co1/3O2/Graphite Prismatic Lithium-Ion Cells

It is desirable to be able to charge automotive batteries at a fast rate, especially for heavy duty commercial vehicles. In this study [1] the effect of fast charging (1C-4C) on ageing was studied on an energy-optimized 25 Ah prismatic NMC(III)/graphite lithium-ion cell cycled at 35°C and 20-80% SOC. Detailed post-mortemanalysis was carried out using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical impedance spectroscopy (EIS). The results show that the effect of charging rate is more complex than earlier described. Even though ageing is more rapid at 3 and 4C charging, no clear trends in degradation with charging rate are observed. Instead, different mechanisms are dominating at the different charging rates. Accelerated lithium plating was observed after cycling at 3C-charging, while extensive gas evolution was the cause to the fast cell impedance rise and capacity fade of the cells cycled at 4C. Graphite exfoliation and accelerated lithium inventory loss point to the graphite electrode as the source of the gas evolution. SEM show cathode particle cracking independent of the charging rate used for the cycling. XPS and EIS generally indicate thicker surface film and larger impedance, respectively, towards the edge of the cells. The results implicate that the ageing rates are too high to be feasible for a battery electric inner-city bus using this type of cell being charged at 3C. However, even though ageing rates for 2C and below are acceptable, it is concluded too slow from the point of view of practical charging time. Fig. Capacity fade vs. number of equivalent full cycles (inset: capacity fade vs. cycling time). Fast-charging effects on ageing for energy-optimized automotive LiNi1/3Mn1/3Co1/3O2/ graphite prismatic lithium-ion cells. Abdilbari Shifa Mussa, Anti Liivat, Fernanda Marzano, Matilda Klett, Bertrand Philippe, Carl Tengstedt, Göran Lindbergh, Kristina Edström, Rakel Wreland Lindström, Pontus Svens, Journal of Power Sources 422, 2019, 175-184.

Molecularly Engineered Nanoporous Membranes for Safety Enhanced Battery Separators

A battery separator physically and electronically separates the anode and cathode but permits Li+ transport between them. Battery separators play a critical role in battery safety by providing, e.g., thermal shutdown functionality in abusive events, or, by preventing lithium metal dendrites or other defects in the cell from penetrating the membrane which can cause internal short circuit leading to uncontrolled thermal runaway, as in the case of the Boeing 787 battery fire incident [1]. One of the challenges with designing safe battery separators is the trade-off between mechanical robustness and porosity/transport properties. For example, high separator tortuosity is good for dendrite resistance but can lead to higher separator resistance [2]. Separator design is further complicated by additional constrains including tolerance to abuse conditions, stable at high voltages (e.g., > 4V), chemically inert to other cell materials, and low cost to meet the performance and cost targets. There is a need to tailor design battery separators that enable high energy/power density with engineered functionality for safety, without adversely affecting performance. Here we present our efforts to develop a nanoporous battery separator that is highly tunable in physical/mechanical properties (e.g., porosity, elastic modulus, toughness) and safety characteristics (e.g., thermal shutdown temperature). Our nanoporous separators are derived from functionalized block copolymers (polyolefins) with low cost precursors [3, 4, 5]. We will also present a hybrid separator concept where the rapid thermal shutdown-capable nanoporous separator developed is hybridized with a highly porous, mechanically and thermally robust separator. This approach renders a hybrid separator technology that affords high energy density, high rate capability, long cycle life and unprecedented safety characteristics for the next generation Li-ion batteries. Figure 1 shows scanning electron microscopy (SEM) images of a representative, synthesized nanoporous polyethylene (NPE) membrane samples, ~ 25 mm in thickness, revealing the desired bicontinuous cubic morphology and percolating pore architecture. Figure 2 shows separator impedance as a function of temperature, for NEP1-3 membrane samples and a commercial separator. An environment (EV) chamber was programmed to increase the temperature at a very low rate of 0.5°C/min for accurate temperature shutdown measurements. The onset of the impedance rise corresponded to ~ 120°C for the NPE separators and ~ 130°C for the commercial separator. The increase of the separator impedance is a result of the separator thermal shutdown, i.e., micropore closing due to the melting/shrinking of the separator, which impedes the ionic motion. It is interesting to note that the separator impedance increased by one to two orders of magnitude at the peak of the thermal shutdown comparing with the initial impedance value. The drastic separator impedance increase associated with the separator thermal shutdown is responsible for providing the safety feature to the otherwise normal operation of Li-ion batteries. The enhanced thermal shutdown features seen in the NPE separators will render earlier, much more rapid and effective thermal shutdown at abusive events (e.g., short circuit, overcharge, etc.), which leads to much improved safety charasteristics for batteries. Our study shows that the molecularly engineered nanoporous membranes are very promising to allow exquisite tuning of mechanical properties (e.g., porosity, elastic modulus, toughness) and safety features (e.g., thermal shutdown temperature). The NPE-based hybrid separator approach will afford an unprecedented performance and safety characteristics for the next generation batteries. Figure 1

Insights from incorporating reference electrodes in symmetric lithium-ion cells with layered oxide or graphite electrodes

Symmetric cells provide complementary means to probe electrochemical processes in lithium-ion batteries. Here, positive and negative electrodes harvested from conventional oxide/graphite cells are cross-paired, and the assembled reference-electrode-bearing symmetric cells are cycled/aged. For graphite symmetric cells, the electrode potentials and impedances remain nearly constant during calendar aging and the parasitic currents are typically small. However, at higher cell voltages when the “positive” graphite potential exceeds 1.0 V vs. Li/Li+, the capacity loss is higher, indicating that even a mild (but prolonged) overdischarge can damage the SEI. For the layered-oxide symmetric cells there are strong parasitic currents and a persistent slide of the electrode potential over time during calendar aging. Significant cell impedance rise, especially at higher hold voltages, is also observed. Curiously, the impedance rise in the “negative” oxide electrode, which experiences potentials below 4.0 V vs. Li/Li+, is greater than in the “positive” oxide electrode that experiences much higher potentials. We postulate that electrolyte oxidation is responsible for the behavior of these oxide symmetric cells, as it supplies electrons (that bind more Li+ into the cathode, causing the potential slide) and protons (that contribute to impedance rise). These insights can guide the development of future lithium-ion cell chemistries.