A new laboratory lithium ion cell in two electrode arrangement has been developed in order to apply in-situ short-term thermal stress tests to both electrodes. Cells were made from commercially available LiCoO 2 cathodes, graphite anodes and electrolyte. A 60 s thermal stress was applied with different temperatures ranging from 100 to 250 • C at the anode side after the cell formation and capacity tests. By comparison of the charge-discharge behavior of the cells before and after the thermal stress, capacity losses, increasing overvoltages and self-discharge have been observed as a function of the stress temperature. For detection of changes in the anode properties scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and computed tomography (CT) characterizations were used, and changes in the morphology and composition of the solid electrolyte interfaces (SEI) layer were observed. Long term cycling and the corresponding capacity and power fade in lithium-ion batteries has recently been extensively studied.1,2 Several aging mechanisms on the single components are proposed in the literature. The degradation reactions are complex, coupled, and dependent on cell chemistry, design and manufacturing procedures used. 3Many studies report the thermal behavior and stability of single components, revealing that elevated temperatures could cause irreversible damage to the materials. [4][5][6][7] Lithium-ion cells face multiple production processes during the fabrication of a high-end battery system, such as contact welding. Depending on the welding technique, the cells are briefly exposed to elevated temperatures of up to several hundred• C. However, to our knowledge no information is available about the influence of such short-term thermal stress conditions on the cell performance and components properties.In the current contribution the anode side of a single lithium cobalt oxide/graphite Li-ion cell was thermally stressed for 60 s at different temperatures and the effects of short-term thermal stress were demonstrated for the first time. To conduct the study a new laboratory cell was developed, allowing in-situ thermal stress tests on both electrodes. The present manuscript is an extended version of the manuscript submitted to the International Meeting on Lithium Batteries 2014 issue of ECS Transaction, 62 (1) 189-196 (2014). ExperimentalMaterial.-Commercially available LiCoO 2 cathodes and graphite anodes from MTI Corporation (Richmond, USA) were used. According to the material specifications provided by the supplier, the anodes contain composite graphite as active material with specific area of 3∼5 m 2 /g and specific capacity of 330 mAh/g. The active material loading is 80 g/m 2 . The active material used in the cathode is LiCoO 2 with specific capacity of 145 mAh/g and loading of 200-250 g/m 2 . A standard aprotic electrolyte LP 30 (BASF, Ludwigshafen, Germany) was used containing 1 M LiPF6 and ethylene carbonate (EC) and dimethyl-carbonate (DMC) in ratio 1:1. A 25 μm trilayerd polypropylene/polyethy...
A new laboratory cell in two electrode arrangement has been developed for this study in order to perform in-situ short-term thermal stress tests on both electrodes. For this study commercially available LiCoO2 cathodes, graphite anodes and LP30 electrolyte has been used. A 60 seconds thermal stress with different temperatures ranging from 100 to 250 °C has been performed at the anode side after the cell formation and capacity tests. By comparison of the charge-discharge behavior of the cells before and after the thermal stress, capacity losses, increasing overvoltages and self-discharge have been observed as a function of the stress temperature. For detection of changes in the anode properties SEM, TGA and CT characterizations were used, and changes in the morphology and composition of the SEI layer were observed.
For several years lithium-ion batteries have been commercially used in small portable devices such as camcorders, laptop computers, cell phones and other electronic devices. Battery lifetime plays only a minor role in such applications due to rapid innovation and strong competition. However, the increasing demand for lithium-ion batteries in the automobile market requires drastic increase in battery lifetime and safety.[1] All compounds in a lithium-ion battery are sensitive to higher temperatures. For example the electrolyte, which is critical in forming the Solid Electrolyte Interface (SEI), is extremely reactive with humid air and has the lowest boiling point of all battery compounds. Equally sensitive is the separator, which has a melting temperature of 130 to 165°C. [2] The majority of existing life-time and performance prognoses are based on long term temperature influences over numerous charging/discharging cycles (such as in a climate chamber at 40°C). Automotive lithium-ion cells must endure multiple production processes during the fabrication of a high-end battery system, such as contact welding, where the cells are exposed to elevated temperatures for a short period of time. This research analyzes the behavior and performance of lithium-ion cells after a short thermal stress. A new laboratory cell in two electrode arrangement has been developed in this study in order to perform in-situ short term thermal stress tests on both electrodes. For the current study commercially available lithium cobalt oxide (LiCoO2) cathodes, graphite anodes and an electrolyte consisting of a solution of lithium salt (e.g. LiPF6) in a mixed organic solvent have been used. This novel cell allows for the exact targeting of various components with heat. The thermal stress has been performed after the cell formation with different temperatures ranging from 60 to 250°C. Electrochemical impedance spectroscopy (EIS) has been used to detect changes, caused by the temporary thermal stress. The morphology and the 3D structure of the thermally stressed electrodes has been examined using Scanning Electron Microscope (SEM) and high resolution Computer Tomography (CT). In addition the thermal characteristics such as the thermal conductivity of the electrodes has been studied using Differential Scanning Calorimetry (DSC) and Laser Flash Analysis (LFA) in order to estimate the temperature propagation in automotive lithium-ion cells during pack assembly. [1] J. Vetter, P. Novák, M.R. Wagner, C. Veit, K.-C. Möller, J.O. Besenhard, M. Winter, M. Wohlfahrt-Mehrens, C. Vogler, A. Hammouche; Ageing mechanisms in lithium-ion batteries. J. Power Sources 147 (2005) 269–281 [2] M. Yoshio, R.J. Brodd, A. Kozawa; Lithium-Ion Batteries, Science and Technologies; Springer (2009)
For several years lithium-ion batteries have been commercially used in portable devices such as camcorders, laptop computers and cell phones. Battery lifetime plays only a minor role in such applications due to rapid product innovation and strong competition. However, the increasing demand for lithium-ion batteries for automotive traction applications requires drastic increase in battery life-time and safety.[1] The majority of the existing life-time and performance prognoses are based on accelerated aging tests at elevated temperatures such as 40 °C, since the temperature plays a crucial role on the battery performance, safety and life-time. However automotive lithium-ion cells must endure multiple production processes during the fabrication of a high-end traction battery system, such as contact welding, where the cells are exposed to elevated temperatures for a short period of time.[2] Up to date there is little information on the temperature propagation within the cell during the short-term thermal stress and also the influence of such short period thermal stress on the cell performance and cyclic ability. For a better understanding of the temperature propagation in the cell, a simulation model based on the thermal material characteristics of a prismatic Li-NiMnCoO2 cell was created in COMSOL Multiphysics®. The thermal characteristics of the battery components are experimentally determined using Laser Flash Analysis (LFA) and Differential Scanning Calorimetry (DSC). In order to validate the modeling approach in this work, we built an experimental setup to measure the temperature propagation within a dummy cell. This dummy cell includes a carbonate solution as electrolyte, yet without a lithium salt. After validating the model is used to describe the temperature propagation after a short-term temperature stress on automotive lithium-ion cells. Furthermore, it’s possible to predict the temperature propagation in the cell with this simulation model, after the short-term stress on different positions on the cell casing surface and at different SOC’s. [1] J. Vetter, P. Novák, M.R. Wagner, C. Veit, K.-C. Möller, J.O. Besenhard,M. Winter, M. Wohlfahrt-Mehrens, C. Vogler, A. Hammouche; Ageing mechanisms in lithium-ion batteries. J. Power Sources 147 (2005) 269–281 [2] M. Yoshio, R.J. Brodd, A. Kozawa; Lithium-Ion Batteries, Science and Technologies; Springer (2009)
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