Researcher:
Esen, Ekin

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PhD Student

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Ekin

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Esen

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Esen, Ekin

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2019 - 20202

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    Performance of high capacity Li-ion pouch cells over wide range of operating temperatures and discharge rates
    (Elsevier Science Sa, 2020) N/A; N/A; N/A; Department of Chemical and Biological Engineering; Alipour, Mohammad; Esen, Ekin; Varzeghani, Amir Rahimi; Kızılel, Rıza; PhD Student; PhD Student; PhD Student; Researcher; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; 114475
    Operating temperature of Lithium-ion batteries (LIBs) significantly affects their electrochemical-thermal performance, cycle life, and cost. This study presents the thermal and electrochemical performance of 20 Ah LiFePO4 cells for 8 current rates (0.2C-5C) at 8 operating temperatures (-20 degrees C to 50 degrees C). Results show that the effects of operating temperature and current rate on cell performance differ above 10 degrees C, between 10 degrees C and 0 degrees C, and at subzero temperatures. Based on the electrochemical impedance spectroscopy (EIS) measurements, significantly higher bulk and charge-transfer resistances in conjunction with the lower diffusion coefficients results in poor battery efficiency at subzero temperatures. Optimum operating condition is 50 degrees C at a rate of 0.2C, in terms of utilized power and capacity, while a considerable power loss and capacity decrease occur below 20 degrees C. Furthermore, increasing the current rate is detrimental above 0 degrees C, whereas it improves cell performance at -10 degrees C, in terms of cell capacity. Moreover, cell temperature reaches an undesirable value at 50 degrees C and 5C rate, thus a thermal management system is necessary for high capacity LiFePO4 cells at higher temperatures and/or at higher C-rates. Additionally, temperature differences on the surface of high capacity cells reach 10 degrees C below room temperature at high current rates which can lead to nonuniform material utilization, and consequently cell failures. Finally, the cycle life of 20 Ah LiFePO4 cells decreases dramatically as discharge current rate increases. (C) 2020 Elsevier B.V. All rights reserved.
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    Investigation of 3-D multilayer approach in predicting the thermal behavior of 20 Ah Li-ion cells
    (Pergamon-Elsevier Science Ltd, 2019) N/A; N/A; Department of Chemical and Biological Engineering; Alipour, Mohammad; Esen, Ekin; Kızılel, Rıza; PhD Student; PhD Student; Researcher; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 114475
    Numerous research groups have adopted a 1D single-layer cell approach to model the thermal behavior of the Li-ion battery systems. However, as the size of a Li-ion cell increases, the 1D single-layer approach is not enough to determine the thermal behavior of the high capacity batteries. In this study, a multilayer approach is proposed to consider the effects of the number of layers on the thermal behavior of the cell. 3D electrochemical-thermal model with multilayer approach is designed and temperature predictions at various discharge rates are calculated. The results are validated at 30 degrees C for various discharge rates. Thermal behavior of the single-layer and multilayer cell approaches are compared with the experimental measurements. The results show that the error of estimates is halved if multilayer approach is applied. The proposed model is also used to study the effects of the number of layers on the temperature non-uniformity of the large sized Li-ion batteries. The results showed that multilayer cell approach represents the thermal behavior of the Li-ion cell more accurately. The study is promising for the development of an efficient thermal management system with a better prediction of the potential hot spots on the single cells and battery packs.