Accelerated Degradation Test Research Articles

Battery Stress Factor Ranking for Accelerated Degradation Test Planning Using Machine Learning

Lithium-ion batteries power numerous systems from consumer electronics to electric vehicles, and thus undergo qualification testing for degradation assessment prior to deployment. Qualification testing involves repeated charge–discharge operation of the batteries, which can take more than three months if subjected to 500 cycles at a C-rate of 0.5C. Accelerated degradation testing can be used to reduce extensive test time, but its application requires a careful selection of stress factors. To address this challenge, this study identifies and ranks stress factors in terms of their effects on battery degradation (capacity fade) using half-fractional design of experiments and machine learning. Two case studies are presented involving 96 lithium-ion batteries from two different manufacturers, tested under five different stress factors. Results show that neither the individual (main) effects nor the two-way interaction effects of charge C-rate and depth of discharge rank in the top three significant stress factors for the capacity fade in lithium-ion batteries, while temperature in the form of either individual or interaction effect provides the maximum acceleration.

Molecular Analysis of the Unusual Stability of an IrNbOx Catalyst for the Electrochemical Water Oxidation to Molecular Oxygen (OER).

Adoption of proton exchange membrane (PEM) water electrolysis technology on a global level will demand a significant reduction of today's iridium loadings in the anode catalyst layers of PEM electrolyzers. However, new catalyst and electrode designs with reduced Ir content have been suffering from limited stability caused by (electro)chemical degradation. This has remained a serious impediment to a wider commercialization of larger-scale PEM electrolysis technology. In this combined DFT computational and experimental study, we investigate a novel family of iridium-niobium mixed metal oxide thin-film catalysts for the oxygen evolution reaction (OER), some of which exhibit greatly enhanced stability, such as minimized voltage degradation and reduced Ir dissolution with respect to the industry benchmark IrOx catalyst. More specifically, we report an unusually durable IrNbOx electrocatalyst with improved catalytic performance compared to an IrOx benchmark catalyst prepared in-house and a commercial benchmark catalyst (Umicore Elyst Ir75 0480) at significantly reduced Ir catalyst cost. Catalyst stability was assessed by conventional and newly developed accelerated degradation tests, and the mechanistic origins were analyzed and are discussed. To achieve this, the IrNbOx mixed metal oxide catalyst and its water splitting kinetics were investigated by a host of techniques such as synchrotron-based NEXAFS analysis and XPS, electrochemistry, and ab initio DFT calculations as well as STEM-EDX cross-sectional analysis. These analyses highlight a number of important structural differences to other recently reported bimetallic OER catalysts in the literature. On the methodological side, we introduce, validate, and utilize a new, nondestructive XRF-based catalyst stability monitoring technique that will benefit future catalyst development. Furthermore, the present study identifies new specific catalysts and experimental strategies for stepwise reducing the Ir demand of PEM water electrolyzers on their long way toward adoption at a larger scale.

The Evaluation Method for Step-Down-Stress Accelerated Degradation Testing Based on Inverse Gaussian Process

In view of the disadvantage that traditional evaluation method of accelerated degradation testing (ADT) complex statistical analysis, in this paper, the randomness and monotonicity of the degradation path for products with high reliability and long lifetime are taken into consideration based on Inverse Gaussian (IG) process. The evaluation method of step-down-stress ADT as well as its reliability function are established based on IG process. At same time, both the simple IG process and IG process with random effects are considered, respectively. The maximum likelihood estimation method and Markov Chain Monte Carlo (MCMC) estimation method are presented to estimate the unknown parameters in the proposed degradation models, respectively. Finally, the proposed evaluation methods are demonstrated by the step-down-stress ADT data of a certain type of missile tank. The results show that the proposed evaluation method is reasonable and valid in this paper. In addition, compared with simple IG process model, IG process with random effects model has many superb properties when dealing with random effects of products in ADT.

Optimal Design of Multi-Stress Accelerated Degradation Test within Irregular Test Region

Motorized spindle is the key functional part of the computer numerical control machine tool and its lifetime determines the reliability level of the machine tool to a great extent. Many efficient plans have been obtained for electronic products but how to design an efficient accelerated degradation test plan for the motorized spindle is still a problem to be solved. In this paper, considering the condition that the loaded stresses of the motorized spindle in practice may not reach their highest levels simultaneously, a novel optimization design method of the accelerated degradation test is proposed within the irregular test region. The orthogonal design theory and the uniform design theory are applied to determine the alternative test plans within the irregular test region for different numbers of stress levels. A numerical example is presented to illustrate the effectiveness of the proposed method. Finally, the sensitivity analysis is conducted to assess the robustness of the optimum plan on parameter variation.

An incipient consistency identification scheme of failure mechanism based on improved grey theory

Accelerated degradation test (ADT) is an effective technique to quantitatively evaluate the life characteristics of high-reliability and long-life products. And the consistency of failure mechanism under different accelerated stress levels is the premise of ADT. In order to identify the consistency of failure mechanism as early as possible and improve the identification accuracy, an incipient consistency identification method of failure mechanism based on improved grey theory is proposed in this paper. Firstly, we reconstruct the background value through the calculation of the integral in the interval. Then the new information priority principle is introduced to improve the construction of initial values in the conventional grey theory. Subsequently, combined with the equal dimension model, the integrated scheme is employed to analyze the enhancement testing data of a resistor in a switching power supply to identify the mutation point of failure mechanism. Compared with the conventional GM (1,1) model, the proposed method has smaller residual, and another identification based on degradation model is also constructed to verify the feasibility and creditability of the proposed method.

An Improved Random Effects Wiener Process Accelerated Degradation Test Model for Lithium-Ion Battery

For the accelerated degradation test (ADT) of lithium-ion battery, the degradation path models are usually applied with the fixed parameters. To optimize the degradation path models, so many battery cells are required for the ADT models based on the degradation path. However, for some lithium-ion batteries with long cycle life and high reliability, the samples are limited due to experimental cost constraints. Meanwhile, owing to the differences in raw materials and manufacturing processes, it is easy to observe variations among the degradation path of lithium-ion battery cells. Fortunately, Wiener process model considering the individual difference can express the variations and be modeled with limited samples for lithium-ion battery. Motivated by this issue, an improved method with random effects Wiener process (REWP) is proposed in this article. First, to verify the degradation process following the Wiener process, the Shapiro-Wilk test is carried out on the basis of a significance level of 0.05. Second, we analyze the varieties of every lithium-ion battery cell. To select a suitable Wiener process model, we apply the coefficient of variation as a measure of random parameters selection for Wiener process. Meanwhile, the maximum likelihood estimation (MLE) is used to optimize parameters of the proposed model. Next, the three different REWP models and general Wiener process model are compared. Finally, to demonstrate the proposed method, the lithium-ion battery cells used for a spacecraft in low Earth orbit (LEO) are conducted for ADTs. The results suggest that the REWP model has a better performance for assessing reliability of lithium-ion battery with long cycle life.

Effect of degradation of filler elements on flexural strength for dental CAD/CAM resin composite materials in water.

Purpose This study aimed to evaluate the effects of degradation on the strength of computer-aided design/computer-aided manufacturing (CAD/CAM) resin composite blocks (RCBs) by subjecting them to accelerated degradation in water and conducting biaxial flexural strength tests.Methods Six commercial RCBs were tested. The RCBs were cut into disks, after which the disks were immersed in purified water. For the aging experiment, the samples were subjected to heat treatment at 37, 60, 70, and 80 °C, in a constant temperature oven and stored statically for 30 d. After the aging experiment, the elements released from the RCB fillers were measured by inductively coupled plasma atomic emission spectroscopy. In addition, the biaxial flexural strength of the RCB fillers was measured after accelerated degradation at 70 °C.Results Si (the main component of the filler) was detected in all the RCB solutions after the aging experiment; however, the type and amount of other elements differed considerably among the RCBs. The flexural strength of some of the RCBs decreased by approximately 20-40% after the accelerated degradation. For most materials, the Weibull coefficient decreased or remained unchanged after the test, whereas it increased in some materials.Conclusions The strength of all the RCBs decreased after the accelerated degradation tests; however, this behavior differed among the materials. In addition, the release of elements from the filler of some of the materials into the water correlated with the decrease in the strength of these materials. These findings indicate that the evaluation of the degradation behavior of RCBs in water is essential for their long-term usage.

Research on Reliability Life Evaluation of Torque Motor based on Performance Degradation

The torque motor problem of reliability. The reliability evaluation of torque motor under the condition of accelerated degradation test is studied. Firstly, the failure mechanism of torque motor is studied, the performance degradation parameters are determined, then the theory of accelerated degradation test is described, the type of accelerated degradation model and the conditions of accelerated test are described. The method and procedure of product reliability analysis using accelerated degradation trajectory method under accelerated degradation test are studied. Finally, the reliability of a torque motor is evaluated and the average life value above 0.9 is calculated

Ultrafine CoRu alloy nanoparticles in situ embedded in Co4N porous nanosheets as high-efficient hydrogen evolution electrocatalysts.

The development of hydrogen evolution reaction (HER) electrocatalysts with outstanding efficiency and favorable stability at all pH values is of great significance but still a dominating challenge toward the development of electrochemical water-splitting technology. Herein, CoRu alloy nanoparticles assembled in Co4N porous nanosheets (named as CoRu@Co4N) have been successfully achieved from Ru(OH)3@Co(OH)2 through a one-step nitridation process. Benefiting from the unique structure, inherent alloy properties and strong alloy-support interaction derived from the in situ transformation, the resultant hybrids exhibit superior HER activities over a wide pH range, achieving very low overpotentials of 13 mV, 44 mV and 15 mV at 10 mA cm-2 under alkaline, neutral and acidic conditions, respectively. Such activities surpass most reported electrocatalysts and are comparable or even transcendent to commercial Ru/C and Pt/C. Furthermore, CoRu@Co4N also exhibits outstanding stability during the accelerated degradation test (ADT) and chronopotentiometry. Our work provides a new approach for designing pH-universal Ru-involved HER electrocatalysts with remarkable efficiency and prominent durability.

Performance Degradation Modeling and Reliability Analysis of Aviation Connectors in Marine Environment

The influence of marine environment on the reliability of a certain type of aviation connectors is studied. Firstly, the step-stress accelerated degradation test which simulates marine environment in South China Sea is designed. And the performance parameter data of four material types of aviation connectors: stainless steel, composite cadmium plating, titanium alloy and aluminum alloy cadmium plating are collected. And then, in order to study the degradation of performance parameters, the mixed effect model is adopted. At last, the reliability lifetime of four material types of aviation connectors are evaluated by means of reliability modeling and analysis. This research provides an effective path for reliability evaluation of aviation connectors, meanwhile it also gives a reference for aviation connectors’ selection.

A nonlinear Wiener degradation model integrating degradation data under accelerated stresses and real operating environment

Remaining useful life (RUL) prediction in real operating environment (ROE) plays an important role in condition-based maintenance. However, the life information in ROE is limited, especially for some long-life products. In such cases, accelerated degradation test (ADT) is an effective method to collect data and then the accelerated degradation data are converted to normal level of accelerated stresses through acceleration factors. However, the stresses in ROE are different from normal stresses since there are some other stresses except normal stresses, which cannot be accelerated, but still have impact on the degradation. To predict the RUL in ROE, a nonlinear Wiener degradation model is proposed based on failure mechanism invariant principle which is the precondition and requirement of an ADT and a calibration factor is introduced to calibrate the difference between ROE and normal stresses. Moreover, the unit-to-unit variability is considered in the concern model. Based upon the proposed approach, the RUL distribution is derived in closed form. The unknown parameters in the model are obtained by a new two-step method through fuzing converted degradation data in normal stresses and degradation data in ROE. Finally, the validity of the proposed model is demonstrated through several simulation data and a case study.

Accelerated degradation tests with inspection effects

This study proposes a framework to analyze accelerated degradation testing (ADT) data in the presence of inspection effects. Motivated by a real dataset from the electric industry, we study two types of effects induced by inspections. After each inspection, the system degradation level instantaneously reduces by a random value. Meanwhile, the degrading rate is elevated afterwards. Considering the absence of observations due to practical reasons, we employ the expectation–maximization (EM) algorithm to analytically estimate the unknown parameters in a stepwise Wiener degradation process with covariates. Moreover, to maintain the level of generality for the adaption of the method in various scenarios, a confidence density approach is utilized to hierarchically estimate the parameters in the acceleration link function. The proposed methods can provide efficient parameter estimation under complex link functions with multiple stress factors. Further, confidence intervals are derived based on the large-sample approximation. Simulation studies and a case study from Schneider Electric are used to illustrate the proposed methods. The results show that the proposed model yields a remarkably better fit to the Schneider data in comparison to the conventional Wiener ADT model.

A doubly accelerated degradation model based on the inverse Gaussian process and its objective Bayesian analysis

ABSTRACT The accelerated degradation test (ADT) is an effective method for evaluating the lifetime of high-reliability products. In this paper, a doubly accelerated degradation model based on the inverse Gaussian process is proposed to characterize the ADT data, and then an objective Bayesian approach is presented to analyze the model. Some important noninformative priors including the Jeffreys prior and reference priors under different group orderings are derived. The propriety of the posterior distributions under each prior is validated. A simulation study is carried out to show the superiority of objective Bayesian approach compared with the parametric Bootstrap method. Finally, the approach is applied to analyze a carbon film data.

Synergistic Effect of Platinum Single Atoms and Nanoclusters Boosting Electrocatalytic Hydrogen Evolution

Maximizing atomic utilization of precious metal-based catalysts is of great significance in heterogeneous catalysis, also becoming a useful strategy to develop efficient electrocatalysts for hydrog...

Selective Laser Thermoregulation System for Accelerated Deg-radation Test of SiC/SiC CMCs

Selective Laser Thermoregulation System for Accelerated Deg-radation Test of SiC/SiC CMCs

Bifunctional Pd‐CeO2 Nanorods/C Nanocatalyst with High Electrochemical Stability and Catalytic Activity for the ORR and EOR in Alkaline Media

AbstractThe catalytic activity and electrochemical stability of Pd‐CeO2‐NR/C (CeO2‐NR: cerium oxide nanorods) for the Oxygen Reduction Reaction (ORR) and the Ethanol Oxidation Reaction (EOR) is shown in alkaline media and compared to Pd/C. Evaluation of catalytic activity for the ORR in a Rotating Ring Disc Electrode (RRDE) set‐up, shows that Pd‐CeO2‐NR/C promotes the reaction with a percentage of hydrogen peroxide production (%H2O2) around 2–4 %, and an electron transfer number (n) close to 4. Tafel plots demonstrates higher mass and specific activities of Pd‐CeO2‐NR/C than Pd/C. Moreover, from cyclic voltammetry tests, Pd‐CeO2‐NR/C shows a higher mass catalytic activity (jm= 697 mA mg−1Pd) for the EOR at a more negative onset potential (Eonset= 0.29 V/RHE) than Pd/C. After Accelerated Degradation Tests (ADT), Pd‐CeO2‐NR/C retains ∼98 % of its Electrochemically Active Surface Area (ECSA), higher than ∼51 % of Pd/C. After ADT, the performance of Pd‐CeO2‐NR/C remains similar for the ORR, while it is significantly higher for the EOR, compared to Pd/C. Thus, the addition of CeO2‐NR enhances the electrocatalytic behavior and stability of Pd towards the ORR and the EOR.

Towards Active and Stable Bifunctional NiCo2O4 Catalysts for O2 Evolution and Reduction in Alkaline Media

It is particularly challenging to find a bifunctional catalyst capable of accelerating both the O2 evolution reaction (OER) and O2 reduction reaction (ORR) in aqueous solutions. The discovery of such a material would bring reversible fuel cells and metal air batteries much closer to technological fruition. However, in a real device, such a catalyst will need to retain its activity across an enormous potential window of at least 1 V over several years. To the best of our knowledge, little is known about the factors controlling the stability of bifunctional catalysts.In this contribution, we investigate the electrochemical activity and stability of a NiCo2O4 catalyst, synthesized at Johnson Matthey as part of EU funded project FLOWCAMP. Using post-mortem techniques, such as inductively coupled plasma mass spectrometry (ICP-MS), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), we provide experimental evidence about catalyst deactivation mechanisms. Results will also include a spectroelectrochemical in-situ UV-Vis study, that provides insights to the reaction mechanism for the OER. Lastly, the activity and stability of NiCo2O4 catalysts is also evaluated in oxygen-electrode prototypes and characterized in a half-cell configuration.In figure 1 is shown the ORR and OER activity of NiCo2O4 before and after accelerated degradation tests (ADT), in rotating disk electrode (RDE) configuration, employing three different electrochemical potential windows: i) 0.6 VRHE - 1 VRHE; ii) 0.6 VRHE - 1.7 VRHE; and iii) VRHE - 1.7 VRHE. As seen by the blue lines, significant ORR deactivation is observed after cycling across both ORR and OER potentials, whereas a 6% decrease in ORR current at 0.7 VRHE is observed after cycling for 1 hour within the ORR potential window. At the same time, degradation is accompanied by significant redox peak changes, as observed in the inset of Figure 1, which could indicate structural changes occurring during the OER. Post-mortem ICP-MS results indicate that catalyst dissolution accompanies this transformation during the OER. Alongside, in-situ UV-vis experiments identified changes in redox species as a function of applied potential, which are further correlated with the electrochemical current to determine the reaction order with respect to the amount of surface oxidized states.In this presentation, I will clarify the factors that control the activity and stability of NiCo2O4 catalysts, by coupling electrochemical measurements with in-situ UV-vis, and post mortem characterization techniques. In my talk, I will focus on understanding the causes for deactivation of the ORR current, which will aid further design of stable ORR and OER catalysts in alkaline media. A cknowledgements: This work is supported by the project ’’FLOWCAMP’’ (www.flowcamp-project.eu) under the European union’s innovation training network (grant agreement 765289).[1] L. Francàs, S. Corby, S. Selim, L. Dongho, C. A. Mesa, R. Godin, E. Pastor, I. E. L. Stephens, K. Choi, J. R. Durrant “Spectroelectrochemical study of water oxidation on nickel and iron oxyhydroxide electrocatalysts,” Nat. Commun., vol. 10, no. 5208, 2019. Figure 1

Lithium Ion Battery Life Analysis in Railway Application

It is well-known that the life of battery is influenced by the temperature, current rate/ pattern, depth of discharge, and chemistry of cell. Capacity and power fade over cycling and storage of lithium ion batteries are still major barriers as their calendar life is 3-5 years whereas target automotive and stationary applications require 10-20years of life time. Battery lifetime is highly dependent on application conditions. In railway application the power pattern is usually similar and repeated, and needs at least 5 years-life warrant. Understanding the relationship between the operating conditions and aging behavior of the batteries is an important task to increase the lifespan. However, it is not easy to quantify the effect of each condition on aging behavior as the aging of batteries involves multiple closely interrelated factors. Accelerated degradation testing with associated modeling and data analysis can effectively be used to predict failure-time distributions. The behaviors of lithium ion cells and aging mechanisms are strongly dependent to the battery cell chemistry and technology so should be chosen in the right application. The lithium ion battery in railway is operated during the whole day time in the mainly outside, and needs high power, high energy characteristics like PHEV and should store the regenerative breaking energy from the traction driving motor.In this study by using an accelerated method the life of railway application battery is evaluated. This study attempts to quantify the strength of the stress factors and the relationship between aging behavior and operating conditions. The accelerating factor is a temperature and depth of discharge, current pattern to understand the effect on life.

Measurement of Activation Energy and Accelerated Degradation Time by Thermal Analysis Methods for Polymeric Insulating Materials

With the development of HVDC systems, there has been much research regarding insulating materials applied in the DC environment. Of particular concern is the degradation of electrical insulation due to external environmental factors caused by the long-term use of the insulation material of a power device. If such degradation continues, a leakage current may flow on the surface of the insulating material, eventually causing a partial discharge and potentially resulting in a major accident. Therefore, it is necessary to understand the long-term reliability of insulation materials. To do this, accelerated degradation tests and lifetime analyses should be performed by measuring the activation energy of insulation materials. There are currently various analytical methods to determine the activation energy, but the values obtained according to the different analysis methods vary. Because there are no established measurement criteria, it is necessary to accurately measure the activation energy of insulation materials. Therefore, in this paper, six analysis methods were performed through thermogravimetric analysis (TGA) to measure the activation energy, which was used to select the degradation time for the accelerated degradation test for which a reliable degradation time for acceleration degradation could be calculated. As a result of the experiment, deterioration acceleration time appeared in the order of PP > PE > PTFE > UPE, and accelerated deterioration of the insulating material through the deterioration time range measured in a future study will be performed to evaluate the life of each insulating materials.

Synthetic Reliability Assessment Model Involving Temperature–Humidity Step-Stress Based on Wiener Process

There are always some difficulties in storage reliability evaluation of high-reliability, long-life, and high-value products, such as the test sample being small, degradation speed being slow, and failure data being inadequate. Temperature–humidity step-stress accelerated degradation test (THSS-ADT) is an effective method to evaluate the reliability of this type of products, but the test data processing is an extremely complex work. The motivation of this paper is to provide a clear, effective, and convenient method to evaluate the reliability on the basis of THSS-ADT data. Considering the stochastic volatility in degradation process, Wiener process is used to modeling the accelerated degradation process. The methods to estimate the parameters of Peck accelerated model and degradation model are discussed under temperature–humidity step-stress. As ordinary optimization algorithms (such as Newton Iteration Method and impelling function method) find it difficult to get the solutions, particle swarm optimization (PSO) method is used to solve the problem of maximum-likelihood estimation. Finally, the proposed methods are demonstrated for two examples, in which one is a numerical simulation, and another is an engineering practice of a microwave power amplifier.