Academic literature on the topic 'Lithium-ion battery cells'

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 167-171).<br>This thesis discusses the design of a control-oriented modeling approach to Lithium- Ion battery modeling, as well as the application of adaptive observers to this structure. It begins by describing the fundamental problem statement of a battery management system (BMS), and why this is challenging to solve. It continues by describing, in brief, several different modeling techniques and their use cases, then fully expounds two separate high fidelity models. The first model, the ANCF, was initiated in previous work, and has been updated with novel features, such as dynamic diffusion coefficients. The second model, the ANCF II, was developed for this thesis and updates the previous model to better solve the problems facing the construction of an adaptive observer, while maintaining its model accuracy. The results of these models are presented as well. After establishing a model with the desired accuracy and complexity, foundational observers are designed to estimate the states and parameters of the time-varying ionic concentrations in the solid electrode and electrolyte, as well as an a-priori estimate of the molar flux. For the solid electrode, it is shown that a regressor matrix can be constructed for the observer using both spatial and temporal filters, limiting the amount of additional computation required for this purpose. For the molar flux estimate, it is shown that fast convergence is possible with coefficients pertaining to measurable inputs and outputs, and filters thereof. Finally, for the electrolyte observer, a novel structure is established to restrict learning only along unknown degrees of freedom of the model system, using a Jacobian steepest descent approach. Following the results of these observers, an outline is sketched for the application of a machine learning algorithm to estimate the nonlinear effects of cell dynamics.<br>by Damas Wilks Limoge.<br>S.M.

The research carried out in this report focuses on the topic of safety of Li-ion battery cells, specifically for automotive applications. Electric vehicle battery safety is a challenge that must be tackled, especially with the rapid electrification of vehicles. Cell abuse testing simulates their failure process under different scenarios. This helps develop a deeper understanding of the failure process, its root cause and associated mechanisms, hence enabling the improvement of their safety. This research has experimentally investigated four abusive conditions; mechanical penetration, external short circuit, cell swelling as a result of overcharge and overcharge in an adiabatic environment. A number of potential industrial applications based on the research findings are also discussed. During nail penetration testing the effect of nail material and diameter were investigated. Firstly, cells were fully penetrated using 10 mm diameter nails with three different materials; copper, steel and plastic. Secondly, cells were penetrated using 10 and 3 mm diameter copper nails. It was found that there was a clear distinction between the outcome of the conducting and non-conducting nails. However, the outcome of using electrically conductive nails suffered from poor reproducibility. Post-mortem examination showed that at the point of penetration the nail dragged the copper current collector in the direction of penetration along with the separator. The hole in the positive electrode looked less circular and the aluminium current collector was not dragged as deep as the copper one. During external short circuit testing the effect of the short resistance and the short duration was investigated. Firstly, cells were short-circuited using a range of resistance values. Secondly, a programmable power supply to control the shorting duration was used. It was found that the degree of damage experienced by a cell during a short is not only defined by the short resistance, but also its duration. The cells were cycleable after the short circuit event and their capacity and resistance increase depended on the short circuit current magnitude and the short duration. Opening the cells after testing and studying their components using SEM showed no change in the surface morphology of the electrodes. During the third set of experiments, purpose-built equipment was designed and built for in-situ volume measurement. The change in cell volume during cycling, overcharge and 10 cycles after the overcharge event was monitored and measured in-situ. The effect of the degree of overcharge and the magnitude of the charging current were studied. After the overcharge event the cycling behaviour of the cells was investigated. Electrochemical Impedance Spectroscopy (EIS) and Direct Current Internal Resistance (DCIR) were used to track the change in resistance. An Equivalent Circuit Model (ECM) was built to investigate the individual components contributing to the cell’s impedance. The overcharge-induced capacity fade was analysed using incremental capacity analysis (ICA). The reversibility of cell volume after swelling was also investigated. Results show that cell swelling and the extent of damage depended on the degree of overcharge and the C-rate. Cell swelling was partially reversible and the cells were cycleable after the overcharge event. Finally, cells were overcharged in ambient and adiabatic conditions. This was carried out to study the effect of heat dissipation on the outcome of an overcharge event. Results highlighted the critical role of heat dissipation from the cell in determining the outcome of the test. The same overcharge regime under different conditions resulted in very different outcomes. Cells overcharged in ambient conditions swelled significantly, but did not vent nor catch fire, whereas, all cells overcharged under adiabatic conditions either ruptured or caught fire. The magnitude of the overcharge current in adiabatic conditions determined the failure mode. Cells overcharged using 0.13 C current ruptured after swelling significantly, but did not catch fire. Cells overcharged with 0.33 and 1.3 C currents were completely combusted.

As wind energy penetration levels increase, there is a growing interest in using storage devices to aid in managing the fluctuations in wind turbine output power. Vanadium-Redox batteries (VRB) and Lithium-Ion (Li-Ion) batteries are two emerging technologies which can provide power smoothing in wind energy systems. However, there is an apparent gap when it comes to the data available regarding the design, integration and operation of these batteries in wind systems. This thesis presents suitable battery electrical models which will be used to assess system performance in wind energy applications, including efficiency under various operating conditions, transfer characteristics and transient operation. A design, sizing and testing methodology for battery integration in converter based systems is presented. Recommendations for the development of operating strategies are then provided based on the obtained results.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 29).<br>The Impact and Crashworthiness Laboratory at MIT has formed a battery consortium to promote research concerning the crash characteristics of new lithium-ion battery technologies as used in automotive applications. Within a broad range of tests, there was a need to perform compression tests with a variable amount of confinement. A spring-loaded detainment device was designed which allows the battery to be confined in the axis perpendicular to compression without completely rigid walls. This provides a testing environment far more similar to the conditions of a real world crash situation. During an automobile crash event, the battery pack acts as a unit where each individual cell may experience a range of stresses from nearby cells or pack walls. An appropriate device was designed in Solidworks and used in the MIT ICL for testing with adjustable confinement during compression testing. MIT's research as a part of the consortium will continue for 3 more years beyond these initial tests. Never the less, the coming computational and constitutive models will be built using initial individual cell testing. Any model of a complete battery pack will use the material properties derived from cell testing.<br>by Eric Roselli.<br>S.B.