Accelerated Cycling Test Research Articles

Failure Analysis and Accelerated Test Development for Rotor Magnetic Bridge of Electric Vehicle Drive Motor

Motor rotor magnetic bridges operate under multiple physical field loads, such as electromagnetic force, temperature, and centrifugal force. These loads can cause fatigue and aging failure of the bridges, especially when the rotor is operating continuously at high speeds and high temperatures. Therefore, the failure analysis and accelerated test cycle development of magnetic bridges is a major aspect of their reliability evaluation. This paper studies rotor multi-physics load transfer characteristics and establishes a rotor magnetic bridge failure physical model. A simulation analysis is conducted from the electromagnetic field, thermal field, structural field, and thermomechanical coupling field to determine the risk point load responses and failure-dominant loads. In addition, the accuracy of the simulation model is verified by actual bench tests. Considering the influence on the rotor bridge’s life under the coupling of multiple failure modes, the fatigue failure model under alternating loads and the fatigue aging coupling failure model are established, respectively. Through a damage analysis, the whole life cycle damage targets for both failure modes are determined, and the test condition levels are screened based on the load frequency distribution and damage distribution. The multi-objective optimization method is used to calculate the number of test cycles and finally develop accelerated test cycle conditions that can reproduce multiple failure modes. This research can provide support for rotor bridge reliability design and verification, as well as product quality development.

Development of Cell Selection and Screening Method and Its Validation Process for the Multi-Combination Battery System

A commercial-off-the-shelf (COTS) cylindrical 18650 Li-Ion cells have been proven to be extremely reliable power sources from many electronic applications for long periods and adopted to the EV applications. The cylindrical cells have been considered a reliable power source for the aerospace battery system, thanks to their high energy and power density. However, some electronic applications' field failure histories and some test programs have indicated that batteries built with cylindrical 18650 cells in multi-cell configurations (series and parallel) have experienced safety issues under various test conditions. Another requirement of the aerospace battery is a long-life cycle under harsh operating conditions. A tiny potential risky outlier cell, which cannot be identified and detected during the cell manufacturing process, can severely affect the multi-combination battery system's safety and reliability, like the EV, ESS, and Aerospace battery system. This paper studied a cell selection and screening method and developed a validation process to evaluate the efficiency and reliability of the cell selection and screening process. A cell selection method includes visual inspection, mass and dimension check, some electrical tests (OCV, CCV, AC Impedance), capacity measurement, and cell level safety test according to widely accepted cell safety standards and battery industrial best practices of the lithium-ion battery. The cell screening method and procedure followed the process and criteria on the NASA technical document (Specification for Acceptance Testing Commercial Lithium-Ion Cells). This program adopted the 6-sigma concept on the data analysis of the cell selection and screening process, which rejects the outlier cells of the 3-sigma level of each test item. The validation process was designed with two test conditions: 1) cycle test on the regular operation of the Human-spaceflight's mission operating conditions and 2) accelerate test condition of the maximum (most severe) cycle condition of the cell makers specification document. The regular operation cycle test was designed to evaluate the screening process's efficiency, whether the 3-sigma level screening is acceptable to the performance of the battery system using all passed cell samples from the screening. The regular cycle test selects four types of 4S string battery groups from different combinations of the cell samples. And it was performed according to the Human-spaceflight's mission operating conditions to validate the 4S can meet the required cycle condition. On the other hand, the accelerated cycle test was designed to identify the difference of cell degradation and capacity decay between the two types of cell combinations by the cycle test. One group use cells randomly selected samples from the non-screen cell, and the other group used selected cells from passed group cell as a control sample. Both 4S strings were cycled at the accelerate test condition, the maximum (most severe) cycle condition of the cell makers specification document. The battery capacity decay and the cell's internal resistance changes by DC pulse technics were checked regularly every 100 cycles during the cycle test.The performance of both 4S was almost similar until 200 cycles. However, the non-screen 4S string's capacity decay speed was much faster and reach death after the 500 cycles, while the screened 4S runs without any severe capacity decline until 800 cycles. EIS (Electrochemical Impedance Spectroscopy) technique was applied to each cell of the 4S string. The DPA (destructive Physical Analysis) and electron microscope analysis were used to identify the electrode's degradation degree and study the cell failure mechanism during the accelerated cycle tests. The DPA and electron microscope analysis (SEM-EDS) identified that gradual damage of the cathode electrode material of the non-screened 4S string during the accelerated cycle test was the leading cause of the cell capacity decay. This research discusses that non-screened 4S string may have different characteristic cell among the four cells in the 4 S string compare to the screened 4S string. That can initiate the stress to the cell and then increase the cell internal resistance, following enhanced cell heat generation and eventually getting the cell imbalance. The cell imbalance and heat generation get the cell getting worse after 200 cycles and eventually kill the cell and 4S sting. This research concludes that the used cell screening process is effective and beneficial as a cell screening process for the multi-cell battery system, especially for the long-term cycle-life battery system, like EV, ESS, and aerospace applications. Figure 1

Study on the influence factors of the cycle life of lead-acid battery in DC system

The high-current accelerated cycle test was used to detect and evaluate the lead-acid battery in the DC system. The results showed that at a temperature of 50 °C, a charge and discharge of 100A, a charge cut-off voltage of 2.4V, and a discharge cut-off voltage of 1.75V were used. The charging time is t1 (t1 is the charging time in the first cycle equal to the charging time when the capacity is discharged). The capacity retention rate is 93.31%, and the charging time is t2 (t2 is the charging capacity in the first cycle is 1.03 times the discharge capacity. The capacity retention rate is 74.72%. Overcharge can reduce the capacity retention rate; the slope during the charging and discharging stages has a good relationship with the capacity retention rate. The slope can be used to represent the capacity retention rate, so the capacity retention can be predicted in advance rate. The research results can realize the detection of DC batteries and provide a basis for battery quality evaluation.

Experimental Assessment of First- and Second-Life Electric Vehicle Batteries: Performance, Capacity Dispersion, and Aging

Nowadays, the reuse of electric vehicle batteries is considered to be a feasible alternative to recycling, as it allows them to benefit from their remaining energy capacity and to enlarge their lifetime. Stationary applications, such as self-consumption or off-grid systems support, are examples of second-life (SL) uses for retired batteries. However, reused modules that compose these batteries have heterogeneous properties, which limit their performance. This article aims to assess the influence of degradation in modules from electric vehicles, covering three main aspects: performance, capacity dispersion, and extended SL behavior. First, a complete characterization of new and reused modules is carried out, considering three temperatures and three discharge rates. In the second stage, intra- and intermodule capacity dispersions are evaluated with new and reused samples. Finally, the behavior during SL is also analyzed, through an accelerated cycling test so that the evolution of capacity and dispersion are assessed. Experimental results show that the performance of reused modules is especially undermined at low temperatures and high current rates, as well as in advanced stages of aging. The intramodule dispersion is found to be similar in reused and new samples, while the intermodule differences are nearly four times greater in SL.

Long-term safety and performance of a novel conical bioresorbable vascular scaffold: insights from in-vitro and in-vivo studies

Abstract Background The phenomenon of size-mismatches between cylindrical stents and tapered vessels is not uncommon in current endovascular interventions which is associated with poor clinical outcomes. Purpose The aim of the present study was to evaluate the mechanical properties of the novel conic BRS and to validate its performance with the support of optical coherence tomography (OCT), quantitative coronary angiography (QCA) and histology up to 2 years in a porcine model. Methods We produced the conical BRS with the four-axis 3D printing system, with a computer-controlled rotational axis (the 4th axis) in addition to the 3 axes of traditional 3D printing systems. Mechanical properties were evaluated by recoil and radial strength, cyclic fatigability testing. Twelve swine that received 12 conic BRS were evaluated by OCT, QCA and histology post-implantation and at 12 and 24 months. Results The in vitro study showed no fractures after accelerated cycle testing over time (at 3.8×108 cycles). The recoil rate of the scaffolds after plate compress test was 14.3±0.61%. There was no significant peri-operative complications. By OCT, 60±21 struts per BRS were recognizable by 2 years. Quantitative coronary angiography showed late luminal loss and percent diameter stenosis were 0.02±0.52 mm and 0.50±16.90% at 2-year follow-up. Histopathological analysis demonstrated mild vessel injuries, inflammatory cell infiltration around struts at 1 and 2 years follow ups. Conclusions The conical BRS showed optimal performance and has the potential to improve clinical outcome. OCT and histological images Funding Acknowledgement Type of funding source: None

Experimental assessment of cycling ageing of lithium-ion second-life batteries from electric vehicles

Abstract The reutilization of batteries from electric vehicles allows to benefit from their remaining energy capacity and to increase their lifespan. The applications considered for the second life of these batteries are less demanding than electric vehicles regarding power and energy density. However, there is still some uncertainty regarding the technical and economic viability of these systems. In this context, the study of the ageing and lifetime of reused batteries is key to contribute to their development. This paper assesses the experimental cycle ageing of lithium-ion modules from different Nissan Leaf through accelerated cycling tests on their second life. The evolution of the internal parameters during ageing and the correlation between them are shown, including the analysis of best fitting curves. In addition, a second-life end-of-life criterion is proposed, based on capacity and internal resistance measurements during cells ageing, which can be applied to real application in order to prevent safety issues. By estimating future values from degradation trends and checking latter measurements, the ageing knee is identified. Results show that the modules operate for at least 2033 equivalent full cycles before reaching their ageing knee. This would mean more than 5 years of operation in a real second-life application, such as a photovoltaic self-consumption installation with daily cycling. Moreover, it is shown that a traditional cell characterisation based on capacity and internal resistance measurements is not enough to predict the durability of a cell during its second life.

Mitigating strategy in lithium dendrite formation in a Li–S cell in accelerated cycling tests

Electrochemical impedance analysis, in-situ dilatometry, in-situ electrochemical calorimetry and ex-situ SEM have been shown to be effective diagnostics for studying formation of lithium dendrites in cells. Effect of lithium polysulfides present in the electrolyte in a Li–S cell, on the suppression of fine-dispersed heterogenous non-planar lithium dendrite precipitations during cycling of lithium symmetric cells was studied in accelerated DC cycling tests by a combination of the above techniques. It is shown that deliberate incorporation of lithium polysulfides in electrolyte solutions leads to decreasing rate of accumulation of fine-dispersed lithium (dendrite precipitations) on the surface of a lithium electrode which results in increasing the cycle life of lithium symmetric cells by 200–250% in accelerated tests, thus enhancing safety. It is demonstrated that electrochemical dilatometry and EC calorimetry are sensitive to changes on the surface of lithium electrode and can be used for early identification of dendrite formation during cycling of lithium electrodes. In-situ electrochemical dilatometry can not only identify formation of Li dendrites at early stages but also quantify the growth rate. The presence of high surface area lithium is more corrosive towards the electrolyte and can be monitored by the use of in-situ EC calorimetry for heat generation by corrosion during a cycle. Cycle life is limited by evenness/continuity of electrolyte solution in cell, which must essentially fill internal volume of the cell (all the pores without leaving any “dry area”).

A Review of Modern Assessment Methods for Metal and Metal-Oxide Based Primers for Substrate Corrosion Protection

Pigmented coatings developed for the corrosion protection of engineering alloys have been successful in the field of corrosion control, and thus are ubiquitous in application. Supporting this success are an array of methods to diagnostically assess these systems and measure their state of degradation. These methods assist the development of next generation coatings, in-service evaluation, and post-mortem analysis of performance. This review comprehensively explores these modern assessment methods, used to screen candidate corrosion prevention pigments, assess pigment protection efficiency, quantify overall pigment effectiveness, and/or predict coating service lifetime. Coating service life assessment is conducted based on the class of coating considered, as categorized by (1) chemical inhibition, (2) galvanic protection, (3) high impedance ion barrier, or a combination of these protection mechanisms. Exciting new in-situ and operando methods are growing in use to enable high fidelity measurement of chemical inhibitor release and deposition, such as micro and in-situ Raman spectroscopy and inductively coupled plasma atomic emission spectrometry (ICP-AES), to name a few. In the galvanic protection coating class, service life and the state of coating performance are now being quantified through methods such as galvanostatic pulse and accelerated cycle testing. Galvanic throwing power is assessed by scanning vibrating electrode technique (SVET), multi-electrode array (MEA), and scanning kelvin probe (SKP). The performance of high impedance ion barrier coatings has traditionally been understood through use of electrochemical impedance spectroscopy (EIS) and equivalent circuit modeling, which have been applied to all coating classes. Finite element analysis (FEA) models the combined effects of coating resistance, water layer thickness, and pigment potential on galvanic coupling and/or inhibitor species release as well. The development of effective corrosion prevention pigments and the in-service evaluation of their efficiency/effectiveness demands a broad collection of techniques. These methods now include new advances in thermodynamic modeling via chemical stability diagrams to assess pigment function in specific conditions, in-situ pH measurement, as well as energy dispersive (EDS) and x-ray photoelectron spectroscopic (XPS) analyses to determine elemental distribution and corrosion product formation. These techniques and more are explored in this review to document the state-of-the-art in the field.

Accelerated cycle life testing and capacity degradation modeling of LiCoO2-graphite cells

Accelerated cycle life testing of lithium-ion batteries is conducted as a means to assess whether a battery will meet its life cycle requirements. This paper presents a study to identify optimal accelerated cycle testing conditions for LiCoO2-graphite cells. A full factorial design of experiment with three stress factors—ambient temperature (10 °C, 25 °C, 45 °C, 60 °C), discharge current rate (C-rate, 0.7C, 1C, 2C), and charge cut-off C-rate (C/5, C/40)—is used to study the effects of these stress factors on battery capacity fade and to obtain the data necessary for decision making. An empirical accelerated degradation model is then developed to capture the characteristics of the two-stage capacity degradation process, along with an accelerated test planning approach.

In vitro mechanical behavior and in vivo healing response of a novel thin-strut ultrahigh molecular weight poly-l-lactic acid sirolimus-eluting bioresorbable coronary scaffold in normal swine

BackgroundNew generation bioresorbable scaffolds (BRS) promise to improve the outcomes of current generation BRS technologies by decreasing wall thickness while maintaining structural strength. This study aimed to compare the biomechanical behavior and vascular healing profile of a novel thin-walled (98 μm) sirolimus-eluting ultrahigh molecular weight BRS (Magnitude, Amaranth Medical) to the Absorb everolimus-eluting bioresorbable vascular scaffold (Abbott Vascular). Methods and resultsIn vitro biomechanical testing showed lower number of fractures on accelerated cycle testing over time (at 21K cycles = 20.0 [19.0–21.0] in Absorb versus 0.0 [0.0–1.0] in Magnitude-BRS). Either Magnitude (n = 43) or Absorb (n = 22) was implanted in 65 coronary segments of 22 swine. Scaffold strut's coverage was evaluated using serial optical coherence tomography (OCT) analysis. At 14 days, Magnitude-BRS demonstrated a higher percentage of embedded struts (97.7% [95.3, 100.0] compared to Absorb (57.2% [48.0, 76.0], p = 0.003) and lower percentage of uncovered struts (0.0% [0.0, 0.0] versus Absorb 5.5% [2.6, 7.7], p = 0.02). Also, it showed a lower percent late recoil (−1.02% [−4.11, 3.21] versus 4.42% [−1.10, 8.74], p = 0.04) at 28 days. Histopathology revealed comparable neointimal proliferation and vascular healing responses between two devices up to 180 days. ConclusionA new generation thin walled (98-μm) Magnitude-BRS displayed a promising biomechanical behavior and strut healing profile compared to Absorb at the experimental level. This new generation BRS platform has the potential to improve the clinical outcomes shown by the current generation BRS.

In Situ Real-Time Mechanical and Morphological Characterization of Electrodes for Electrochemical Energy Storage and Conversion by Electrochemical Quartz Crystal Microbalance with Dissipation Monitoring.

Quartz crystal microbalance with dissipation monitoring (QCM-D) generates surface-acoustic waves in quartz crystal plates that can effectively probe the structure of films, particulate composite electrodes of complex geometry rigidly attached to quartz crystal surface on one side and contacting a gas or liquid phase on the other side. The output QCM-D characteristics consist of the resonance frequency (MHz frequency range) and resonance bandwidth measured with extra-ordinary precision of a few tenths of Hz. Depending on the electrodes stiffness/softness, QCM-D operates either as a gravimetric or complex mechanical probe of their intrinsic structure. For at least 20 years, QCM-D has been successfully used in biochemical and environmental science and technology for its ability to probe the structure of soft solvated interfaces. Practical battery and supercapacitor electrodes appear frequently as porous solids with their stiffness changing due to interactions with electrolyte solutions or as a result of ion intercalation/adsorption and long-term electrode cycling. Unfortunately, most QCM measurements with electrochemical systems are carried out based on a single (fundamental) frequency and, as such, provided that the resonance bandwidth remains constant, are suitable for only gravimetric sensing. The multiharmonic measurements have been carried out mainly on conducting/redox polymer films rather than on typical composite battery/supercapacitor electrodes. Here, we summarize the most recent publications devoted to the development of electrochemical QCM-D (EQCM-D)-based methodology for systematic characterization of mechanical properties of operating battery/supercapacitor electrodes. By varying the electrodes' composition and structure (thin/thick layers, small/large particles, binders with different mechanical properties, etc.), nature of the electrolyte solutions and charging/cycling conditions, the method is shown to be operated in different application modes. A variety of useful electrode-material properties are assessed noninvasively, in situ, and in real time frames of ion intercalation into the electrodes of interest. A detailed algorithm for the mechanical characterization of battery electrodes kept in the gas phase and immersed into the electrolyte solutions has been developed for fast recognition of stiff and viscoelastic materials in terms of EQCM-D signatures treated by the hydrodynamic and viscoelastic models. Working examples of the use of in situ hydrodynamic spectroscopy to characterize stiff rough/porous solids of complex geometry and viscoelastic characterization of soft electrodes are presented. The most demonstrative example relates to the formation of solid electrolyte interphase on Li4Ti5O12 electrodes in the presence of different electrolyte solutions and additives: only a few cycles (an experiment during ∼30 min) were required for screening the electrolyte systems for their ability to form high-quality surface films in experimental EQCM-D cells as compared to 100 cycles (200 h cycling) in conventional coin cells. Thin/small-mass electrodes required for the EQCM-D analysis enable accelerated cycling tests for ultrafast mechanical characterization of these electrodes in different electrolyte solutions. Hence, this methodology can be easily implemented as a highly effective in situ analytical tool in the field of energy storage and conversion.

Die degradation effect on aging rate in accelerated cycling tests of SiC power MOSFET modules

In order to distinguish the die and bond wire degradations, in this paper both the die and bond wire resistances of SiC MOSFET modules are measured and tested during the accelerated cycling tests. It is proved that, since the die degradation under specific conditions increases the temperature swing, bond wires undergo harsher thermo-mechanical stress than expected. The experimental results confirm the die-related thermal failure mechanism. An improved degradation model is proposed for the bond-wire resistance increase in case of die degradation.

A novel medium-temperature form-stable phase change material based on dicarboxylic acid eutectic mixture/expanded graphite composites

Low stability, reliability, and corrosion are considerable challenges to widespread application of succinic acid (SA) as phase change material (PCM). Here, we present a novel medium-temperature form-stable phase change material (FSPCM) aiming to eliminate these obstacles. In this study, FSPCM was fabricated by adsorbing eutectics of adipic acid (AA) and SA into expanded graphite (EG). The molar ratio of AA and SA in eutectics was determined to be 7:3, and the optimal mass ratio of EG in FSPCM is ca. 0.1. The composite was characterized by diffraction scanning calorimetry, scanning electron microscopy, Fourier transform infrared spectrometer, X-ray diffractometer, and thermal gravimetric analyzer. The results showed that the FSPCM melts at ca. 135°C with latent heat storage of 206J/g. No notable change of thermal behavior in FSPCM was observed after experienced 100 accelerated cycle test. Compared to SA, both the stability and reliability were promoted in FSPCM. Besides, the leakage of dicarboxylic acid was prevented, thus the corrosion was alleviated.It is envisioned that the as-prepared FSPCM have considerable potential in medium-temperature latent heat storage.

Microencapsulation through thermally sintering Pickering emulsion-based colloidosomes.

Microcapsules of a phase change material synthesized by thermally sintering Pickering emulsion-based colloidosomes were demonstrated. The protocol included three steps: (1) monodispersive poly(glycidyl methacrylate) (PGMA) microspheres were prepared by dispersive polymerization and were endowed with a contact angle of 63.4° for oil-in-water Pickering stabilization by hydrolysis. (2) By phase separation during Pickering emulsion polymerization, microcapsules with a structure of a single PCM core and a PGMA armored polystyrene shell were fabricated. (3) Thermal sintering was performed to fuse the polystyrene and PGMA microspheres into an integral shell of the microcapsules. The durability of the microcapsules before and after sintering was investigated by a suspension test (in water and ethanol) and an accelerated thermal cycling test. The sintering reduced the percentage of leaked dodecanol from 19.6% to 10.3% in the suspension test in ethanol and from 10.4% to 2.8% in the accelerated cycling test. These results verified that the sintering process endowed the prepared microcapsules with better tightness and durability.

A Review on the Biomechanical Effects of Fatigue on the Porcine Bioprosthetic Heart Valve.

Characterization of the mechanisms of degeneration of porcine bioprosthetic heart valves (BHV) during long-term cyclic loading is required for predicting and ultimately preventing their failure. Isolation of purely mechanical effects from host biological ones is a necessary first step in understanding the fatigue process as a whole. Thus, in this review we focus on mechanical factors alone as a means of isolating their role in altering biomechanical properties and ultimately their contribution to the fatigue damage process. Mechanical evaluations included tension controlled biaxial, 3-point flexural, and uniaxial failure tests performed on cuspal tissue following 0, 50, 100, 200, and 300 × 106 in vitro accelerated test cycles. Overall, biaxial mechanical results indicate a decreasing radial extensibility that can be explained by stiffening of the effective collagen fiber network as well as a small decrease in the splay of the collagen fibers. Moreover, these results suggest that the loss in flexural rigidity with fatigue that we have previously measured (ASAIO 1999; 45:59-63) may not be because of loss of collagen stiffness alone, but also to fiber debonding and degradation of the amorphous extracellular matrix. We discuss the implications of these results that point toward the development of chemical-treatment methods that seek to maintain the integrity of the amorphous extracellular matrix to ultimately extend BHV long-term durability.

Comparative Characterization of Biomechanical Behavior and Healing Profile of a Novel Ultra-High-Molecular-Weight Amorphous Poly-l-Lactic Acid Sirolimus-Eluting Bioresorbable Coronary Scaffold.

Clinically available bioresorbable scaffolds (BRS) rely on polymer crystallinity to achieve mechanical strength resulting in limited overexpansion capabilities and structural integrity when exposed to high-loading conditions. We aimed to evaluate the biomechanical behavior and vascular healing profile of a novel, sirolimus-eluting, high-molecular-weight, amorphous poly-l-lactic acid-based BRS (Amaranth BRS). In vitro biomechanical testing was performed under static and cyclic conditions. A total of 99 devices (65 Amaranth BRS versus 34 Absorb bioresorbable vascular scaffold [BVS]) were implanted in 99 coronary arteries of 37 swine for pharmacokinetics and healing evaluation at various time points. In the Absorb BVS, the number of fractures per scaffold seen on light microscopy was 6.0 (5.0-10.5) when overexpanded 1.0 mm above nominal values (≈34%). No fractures were observed in the Amaranth BRS group at 1.3 mm above nominal values (≈48% overexpansion). The number of fractures was higher in the Absorb BVS on accelerated cycle testing over time (at 24K cycles=5.0 [5.0-9.0] Absorb BVS versus 0.0 [0.0-0.5] Amaranth BRS). Approximately 90% of sirolimus was found to be eluted by 90 days. Optical coherence tomography analysis demonstrated lower percentages of late scaffold recoil in the Amaranth BRS at 3 months (Amaranth BRS=-10±16.1% versus Absorb BVS=10.7±13.2%; P=0.004). Histopathology analysis revealed comparable levels of vascular healing and inflammatory responses between both BRSs up to 6 months. New-generation high-molecular-weight amorphous poly-l-lactic acid scaffolds have the potential to improve the clinical performance of BRS and provide the ideal platform for the future miniaturization of the technology.

Capacity Fade of Lithium-Ion Batteries upon Mixed Calendar/Cycling Aging Protocol

Energy and power fade of lithium-ion batteries over time is a cause of complaints from Electric and Hybrid vehicles customers. Car manufacturers strive to improve accuracy of battery performance degradation predictions, in order to reduce warranty costs. Currently, these predictions are mainly based on accelerated aging tests in cycling mode or on calendar tests. However, testing protocols with combination of calendar and cycling modes representing the usage of a vehicle in real life application are not much used. In this paper, a mixed aging protocol combining cycling and calendar repetitive phases is elaborated. Experimental results obtained on a LIB technology are presented and discussed in comparison with conventional accelerated cycling tests at the same conditions.

Evolution of the Surface and Subsurface Chemical Environment of LixNi0.8Co0.15Al0.5O2 electrodes

The nickel-based layered positive electrode, LiNi0.8Co0.15Al0.05O2 (NCA) has a high discharge capacity of ~ 200 mAhg-1 making it promising for potential electric vehicle applications. However, NCA displays drastic capacity fade with cycling. Accelerated cycling tests at elevated temperatures have shown that NCA electrodes undergo significant power fading. The significant power fading has been largely attributed to the formation of insulating and electrochemically inactive phases at the NCA surface. These include Li2CO3 surface species and a NiO-like rocksalt phase at particle surface due to oxygen loss. The literature of NCA surface and subsurface studies have highlighted the complexity of studying electrodes, with many reactions occurring that may not be inherent to NCA. Here we report on our studies of the surface and subsurface of NCA electrodes with and without a binder additive (i.e. PVDF) as a function of initial charging and cycling. The chemical composition and transition metal oxidation states were determined from a combination of x-ray photoelectron and absorption spectroscopy techniques. Our results reveal dramatic differences in the surface environments between our NCA electrodes with and without binder. Our results suggest that the PVDF may play a more significant role in degrading the surface of the NCA i.e. oxygen loss, than previously thought. We also report our surface analysis of our extended cycled NCA binder free electrodes. This work was supported as part of NECCES, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001294.

Study on the electrode's balance for electrochemical double-layer capacitor

Cube-electrochemical double-layer capacitors with different electrode thickness have been prepared from composite activated carbons via slurry, vacuum dring, aging formation and so on. After accelerated cycle-lifetime's testing, we comprehensively analyzed the changes in specific capacitance and internal resistance. The result shows that after been accelerated cycling test for a long time, the separator became yellow and black, what's more, when the positive thickness was over negative side, the EDLC would embrace a more stable and much little expansion rate. Furthermore, if the negative side was fixed and the electrode balance coefficient is 0.2, the EDLC would exhibit an optimal performance.

Study of Supercapacitor Aging and Lifetime Estimation According to Voltage, Temperature, and RMS Current

Due to its capacity to store or supply energy with high power, the supercapacitor is becoming an attractive component. Because of the electrostatic nature of energy storage, the endurance of this component toward repetitive charge and discharge cycles is relatively high. The goal of this paper is to demonstrate that cycling has an impact on the degradation of the supercapacitor and, as a result, on its lifetime. Based on accelerated cycling tests, some supercapacitors were studied using a dedicated test bench. Temperature, voltage, and current, which are the parameters that accelerate aging, are monitored. In fact, observations during the cycling tests show an important acceleration in the degradation compared with a similar static test having the same voltage and core temperature but without cycling. This paper proposes a method to quantify the acceleration of aging during a cycling phase.