Rapid discharge failure prediction model for solar charged lithium-ion batteries

Thesis submitted in partial fulfillment of the requirements for the Degree of Master of Science in Information Technology (MSIT) at Strathmore UniversityLithium-ion batteries are continually being deployed in many appliances. This is due to their high energy density and cost effectiveness. Most of these have been around for years in portable devices such as mobile phones. With the onset of smartphones, there is an ever increasing need to have batteries with superior performance. This can be viewed from the context of the need for fast charging and an ability to support a fully multitasked smartphone. Lithium-ion batteries have become the defacto battery type in many of these and similar applications due to their inherent characteristics. They have found use in not just mobile phones but also in innovative products designed to light homes as well provide for mobile phone charging in rural Africa. These products include a battery pack of Lithium-ion batteries cells charged by solar panels. There are a number of challenges facing the companies dealing with such products. There is a need to provide a superior product while at the same time ensure efficiency in the production line so as to bring down costs. All these need to be done while maintaining the elusive customer loyalty. One of the major issues faced is accelerated degradation which cannot be noticed using conventional approaches. Currently the main mode of triage for failure is visualization of graphs from data collected from the sensors attached to the batteries and observing for irregularities in the charge and discharging patterns. Existing literature talks about models used on linear data for forecasting in various fields of research. It also proposes an approach to predict battery life in batteries used on various applications such as hybrid electric vehicles. The proposed method will take advantage of predictive analytics in time series analysis to predict failure based on data from the batteries. Data from the batteries spanning 30 days was used to generate gradients of daily charging gradients. These were used as the training data with a binary class of faulty and good. We are able to train a model using the nearest neighbor algorithm to obtain over 80% accuracy with only a sample of 200 batteries data

유기발광 디스플레이 수명 모델 제안 및 모델 검증 체계 연구

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 기계항공공학부, 2018. 2. 윤병동.Despite the advantages of organic light-emitting diode (OLED) displays over liquid crystal displays, OLED displays suffer from reliability concerns related to luminance degradation and color shift. In particular, existing testing schemes are unable to reliably estimate the lifetime of large OLED displays (i.e., displays of 55 inches or larger). The limited number of test samples and the immature technology result in great hurdles for timely product development. This study proposes a statistical approach to develop a lifetime model for OLED panels. The proposed approach incorporates manufacturing and operational uncertainties, and accurately estimates the lifetime of the OLED panels under normal usage conditions. The proposed statistical analysis approach consists of: (1) design of accelerated degradation tests (ADTs) for OLED panels, (2) establishment of a systematic scheme to build bivariate lifetime models for OLED panels, (3) development of two bivariate lifetime models for OLED panels, and (4) statistical model validation for the heat dissipation analysis model for OLED TV design. This four-step statistical approach will help enable accurate lifetime prediction for large OLED panels subjected to various uncertainties. Thereby, this approach will foster efficient and effective OLED TV design to meet desired lifespan requirements. Furthermore, two bivariate acceleration models are proposed in this research to estimate the lifetime of OLED panels under real-world usage conditions, subject to manufacturing and operational uncertainties. These bivariate acceleration models take into account two main factors—temperature and initial luminance intensity. The first bivariate acceleration model estimates the luminance degradation of the OLED panelthe second estimates the panels color shift. The lifespan predicted by the proposed lifetime model shows a good agreement with experimental results. Ensuring the color shift lifetime is a great hurdle for OLED product development. However, at present, there is no effective way to estimate the color shift lifetime at the early stages of product development while the product design is still changing. The research described here proposes a novel scheme for color shift lifetime analysis. The proposed method consists of: (1) a finite element model for OLED thermal analysis that incorporates the uncertainty of the measured surface temperature, (2) statistical model validation, including model calibration, to verify agreement between the predicted results and a set of experimental data (achieved through adjustment of a set of physical input variables and hypothesis tests for validity checking to measure the degree of mismatch between the predicted and observed results), and (3) a regression model that can predict the color shift lifetime using the surface temperature at the early stages of product development. It is expected that the regression model can substantially shorten the product development time by predicting the color shift lifetime through OLED thermal analysis.Chapter 1. Introduction 1 1.1 Background and Motivation 1 1.2 Overview and Significance 2 1.3 Thesis Layout 6 Chapter 2. Literature Review 8 2.1 Accelerated Testing 8 2.2 Luminance Degradation Model for OLEDs 12 2.3 Color Shift of OLEDs 14 2.4 Verification and Validation Methodology 16 Chapter 3. OLED Degradation 28 3.1 Chromaticity and the Definition of Color Shift Lifetime 30 3.2 Degradation Mechanism 31 3.2.1 Luminance Degradation Mechanism 33 3.2.2 Color Shift Mechanism 34 3.3 Performance Degradation Models 36 3.3.1 Performance Degradation Model 36 3.3.2 Performance Color Shift Model 38 3.4 Acceleration Model 38 Chapter 4. Acceleration Degradation Testing (ADT) for OLEDs 42 4.1 Experimental Setup 42 4.2 Definition of the Time to Failure 46 4.2.1 The Time to Failure of Luminance 46 4.2.2 The Time to Failure of Color Shift 47 4.3 Lifespan Test Results 50 Chapter 5. Bivariate Lifetime Model for OLEDs 53 5.1 Fitting TTF Data to the Statistical Distribution 53 5.1.1 Estimation of Lifetime Distribution Parameters 53 5.1.2 Estimation of the Common Shape Parameter 58 5.1.3 Likelihood-Ratio Analysis 62 5.2 Bivariate Lifetime Model 64 5.2.1 Luminance Lifetime Model 64 5.2.2 Color Shift Lifetime Model 66 5.3 Validation of the Lifetime Model 67 Chapter 6. Statistical Model Validation of Heat Dissipation Analysis Model 77 6.1 Estimation Method for TTF using Surface Temperature 79 6.2 Thermal Analysis Model for OLED Displays 81 6.3 Statistical Calibration using the EDR Method 82 6.4 Validity Check 87 6.5 Results and Discussion 90 Chapter 7. Case Study 93 7.1 Computational Modeling 93 7.2 Estimation of Color Shift 95 7.3 Estimation of Luminance Degradation 96 Chapter 8. Contributions and Future Work 98 8.1 Contributions and Impacts 98 8.2 Suggestions for Future Research 103 References 104Docto

Characterisation, modelling and management of lithium-sulphur batteries for spacecraft applications

The lithium-sulphur couple has such a high theoretical energy density that, in principle, it could contribute significant weight and cost savings for launching a spacecraft. The principle aim of this study was to determine the suitability of lithium-sulphur cell technology for space industry applications by considering all areas of performance, modelling and electronic protection requirements. This thesis is split into three main areas. Firstly, after examining the background material, the current state of the lithium-sulphur electrochemistry is analysed in detail. It is of great importance to have a clear understanding of the cell’s electrochemical and chemical interactions as they can be used to explain the performance characteristics of the cell later in the work. On completion of the electrochemical analysis the thesis then goes on to describe a set of electrical and thermal characterisation tests, the results of which are used to establish a novel equivalent circuit model of a Li-S battery. The equivalent circuit modelling method was chosen mainly for its ease of implementation into a full power system model and for its adaptability to future cell variations, both of which are important for the intended application. The resultant model uses electrical, thermal and “split capacity” domains to successfully predict cell performance. Further characterisation testing results are then analysed with a view to specifying the electrical protection requirements of a Li-S battery management system suitable for different space industry applications. It was determined that the Li-S cell has safety and protection needs that exceed that of lithium-ion batteries, as well as requiring a robust housing structure, reducing the energy density of the battery pack. The conclusion of the work is that, although the Li-S cell holds promise for the future, the current state of the cell’s degradation characteristics prevents it from competing with lithium-ion cells in its current forma

EFFECTS OF EXTERNAL PRESSURE ON SOLID STATE DIFFUSION OF LITHIUM IN LITHIUM-ION BATTERIES

Electrochemical-mechanical effects in lithium-ion batteries refer to the phenomena that give way to the piezo-electrochemical properties observed during intercalation of lithium into lithium-ion battery electrodes. By applying perturbations to the external pressure of a lithium-ion battery, the dynamics of lithium intercalation, in particular the diffusion rate of lithium-ions onto and out of battery electrodes, can be studied with respect to the open-circuit potential and the applied hydrostatic pressure. In this study, commercial thin film batteries were subjected to tests in a low-pressure chamber and in a dynamic materials analyzer simulating hydrostatic pressures between 0 and 115 KPa. Under each hydrostatic pressure condition, galvanostatic intermittent titration technique (GITT) was performed to measure and correlate lithium diffusivity to battery strain, open-circuit potential, and applied hydrostatic force. From the data a model was developed for lithium diffusivity as a function of open circuit potential and hydrostatic pressure. The implications of this work extend from the use of lithiated graphite for energy harvesting and actuation to policy and regulations for how batteries should be safely transported. To provide some insight into how this work can be applied to policy actions, current international regulations regarding the air transport of lithium-ion batteries are critically reviewed. The pre-shipping tests are outlined and evaluated to assess their ability to fully mitigate risks during battery transport. In particular, the guidelines for shipping second-use batteries are considered. Because the electrochemical state of previously used batteries is inherently different from that of new batteries, additional considerations must be made to evaluate these types of cells. Additional tests are suggested that evaluate the risks of second-use batteries, which may or may not contain incipient faults. Finally, this work is extended to supercapacitors through the development of a model to predict the oxidation of functional groups on the surface of graphite electrodes with respect to operational temperature and voltage. This model is used to predict the operational life of supercapacitors and validates the model on accelerated testing data. The final results are compared to previous models proposed in literature

NASA Tech Briefs, August 1991

Topics: New Product Ideas; NASA TU Services; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences; Life Sciences

Calendar Aging and Lifetimes of LiFePO4 Batteries and Considerations for Repurposing

In response to rising petroleum prices, the demand for lower emissions standards for vehicles, and better vehicle fuel economy, the market for hybrid and electric vehicles is expanding. These systems incorporate advanced battery systems which store and provide energy in the vehicle. Over time, though, cells degrade and lose capacity in accordance with two different aging phenomena: cycling and calendar aging. It is imperative to understand how these degradation phenomena occur as the loss in capacity results in a loss in vehicle range. Through understanding how these phenomena occur, mitigation efforts can be designed to prevent or lessen their effects. This thesis will focus primarily on studying the effects of calendar aging on commercial LiFePO4 cells. Cells are aged at varying temperatures and states of charge (SOC) to determine the extent of capacity fade and degradation. Additional testing methods are then utilized to attempt to determine which aging phenomena are promoting the losses within the cell. Capacity loss in cells stored at high temperature and fully charged conditions resulted in faster degradation rates. Temperature had the most significant role in the degradation of the cell and then the cell’s SOC. Comparing capacity losses between cells stored at the same temperature, but with different SOCs, found that the cells with higher SOC experienced increased rates of degradation in comparison to their fully discharged counterparts. In addition, storage at high SOC and high temperatures promoted such severe losses that the cells in question were unable to recapture capacity that they had lost reversibly. The primary degradation mode for the cells was the loss of cyclable lithium, and was found to occur under all of the storage conditions. Cells stored at much more severe conditions, though, also demonstrated a loss of active material at the anode. The extent of the loss of the active material was largely predicated on whether or not the cell was stored at fully charged or discharged conditions. Storage of lithium-ion batteries at high temperatures has a dramatic effect on the continual usage of the cells after storage conditions have changed. Despite shifting temperatures or states-of-charge to a lower value, the initial storage conditions leads to increased degradation rates throughout the cell life. Thus, the history of storage for the cell must be also be taken into account when considering losses in capacity

Innovation for maintenance technology improvements

A group of 34 submitted entries (32 papers and 2 abstracts) from the 33rd meeting of the Mechanical Failures Prevention Group whose subject was maintenance technology improvement through innovation. Areas of special emphasis included maintenance concepts, maintenance analysis systems, improved maintenance processes, innovative maintenance diagnostics and maintenance indicators, and technology improvements for power plant applications

Customers' switching behaviour towards remanufactured auto-products, with particular reference to the automotive industry in Thailand

The automotive industry is a major manufacturing sector in the economy of Thailand. However, industrialisation in Thailand, largely based on the traditional ‘take-make-dispose’ linear economy model, has not only placed increased pressure on the resource base of the economy, but it has also resulted in increased dependency of the industrial sector on large and foreign enterprises and in environmental pollution due to end-of-life vehicles. Dependence of industry and the economy at large on the linear economy model has been at the heart of structural unsustainability underlying the Thai economy. Environmental pollution is also a cause for concern. Hence the case for transition to a circular economy. Transition of the auto-sector in Thailand to the CE model is not without barriers that arise in the market. These become apparent when considering the range of factors associated with prevailing consumption and production behaviours that influence the transition process. In this study, the factors that influence the behaviours of customers and producers of automotive products are investigated. This study on the switching behaviour of customers is based on the ‘Push-Pull-Mooring’ (PPM) theory of migration; and for investigation of the survey data, the structural equation model (SEM) is adopted. The findings of the demand-side study of the automotive remanufacturing market show that the decision of customers to switch to remanufactured products is significantly related to the special benefits and environmental benefits deriving from the use of these auto products, consumers’ attitudes towards such products, and the risk of obsolescence that would be attached to remanufactured auto-products. Particularly, the suspicious attitude of customers towards the so-called ‘like-new’ remanufactured products were found to have a significant direct and indirect influence on their switching intentions. Meanwhile, the findings of the supply-side study indicate that the factors influencing auto-manufacturers to induce remanufacturing auto-businesses in Thailand are product maturity, financial costs, lack of skilled labour and technical aspects. A sustainable business model (SBM) for remanufacturing and ‘circular’ practices in the Thai automotive industry is developed as a policy and decision framework based on the empirical findings of the study. The SBM is developed as a practical business model for remanufacturers to launch ‘circular’ businesses in the auto sector in Thailand.The automotive industry is a major manufacturing sector in the economy of Thailand. However, industrialisation in Thailand, largely based on the traditional ‘take-make-dispose’ linear economy model, has not only placed increased pressure on the resource base of the economy, but it has also resulted in increased dependency of the industrial sector on large and foreign enterprises and in environmental pollution due to end-of-life vehicles. Dependence of industry and the economy at large on the linear economy model has been at the heart of structural unsustainability underlying the Thai economy. Environmental pollution is also a cause for concern. Hence the case for transition to a circular economy. Transition of the auto-sector in Thailand to the CE model is not without barriers that arise in the market. These become apparent when considering the range of factors associated with prevailing consumption and production behaviours that influence the transition process. In this study, the factors that influence the behaviours of customers and producers of automotive products are investigated. This study on the switching behaviour of customers is based on the ‘Push-Pull-Mooring’ (PPM) theory of migration; and for investigation of the survey data, the structural equation model (SEM) is adopted. The findings of the demand-side study of the automotive remanufacturing market show that the decision of customers to switch to remanufactured products is significantly related to the special benefits and environmental benefits deriving from the use of these auto products, consumers’ attitudes towards such products, and the risk of obsolescence that would be attached to remanufactured auto-products. Particularly, the suspicious attitude of customers towards the so-called ‘like-new’ remanufactured products were found to have a significant direct and indirect influence on their switching intentions. Meanwhile, the findings of the supply-side study indicate that the factors influencing auto-manufacturers to induce remanufacturing auto-businesses in Thailand are product maturity, financial costs, lack of skilled labour and technical aspects. A sustainable business model (SBM) for remanufacturing and ‘circular’ practices in the Thai automotive industry is developed as a policy and decision framework based on the empirical findings of the study. The SBM is developed as a practical business model for remanufacturers to launch ‘circular’ businesses in the auto sector in Thailand

Designing wearable sensors for Preventative Health: An exploration of material, form and function

The financial burden on global healthcare systems has reached unprecedented levels and as a result, attention has been shifting from the traditional approach of disease management and treatment towards prevention (Swan, 2012). Wearable devices for Preventative Health have become a focus for innovation across academia and industry, thus this thesis explores the design of wearable biochemical and environmental sensors, which can provide users with an early warning, detection and monitoring system that could integrate easily into their existing lives. The research aims to generate new practical knowledge for the design and development of wearable sensors and, motivated by the identification of compelling design opportunities, merges three strands of enquiry. The research methodology supports this investigation into material, form and function through the use of key practice-based methods, which include Participatory Action Research (active immersion and participation in a particular community and user workshops) and the generation and evaluation of a diverse range of artefacts. Based on the user-centred investigation of the use case for biochemical and environmental sensing, the final collection of artefacts demonstrates a diverse range of concepts, which present biodegradable and recyclable nonwoven material substrates for the use in non-integrated sensors. These sensors can be skin-worn, body-worn or clothing-attached for in-situ detection and monitoring of both internal (from the wearer) and external (from the environment) stimuli. The research proposes that in order to engage a broad section of the population in a preventative lifestyle to significantly reduce the pressure on global healthcare systems, wearable sensors need to be designed so they can appeal to as many users as possible and integrate easily into their existing lifestyles, routines and outfits. The thesis argues that this objective could be achieved through the design and development of end-of-life considered and cost-effective substrate materials, non-integrated wearable form factors and meticulous consideration of a divergent range of user needs and preferences, during the early stages of design practice

NASA Tech Briefs, December 1994

Topics: Test and Measurement; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery; Fabrication; Mathematics and Information Sciences; Life Sciences; Books and Report