A full physics stack model combined with a detailed thermal model are applied to simulate voltage and temperature profiles of 26700 sized commercial Li-ion power cells. A wide range of currents (3A → 40A) and a wide range of temperatures (−20 • C → 40 • C) are considered. The conventional stack model is augmented to include pseudo-capacitance effects in order to get a reasonable agreement with the measured data. Least squares refinement of 21 data sets is used to determine a number of material properties and their temperature dependence. Practical guidelines are described for choosing input material properties and for using the least squares method. All 21 data sets are successfully simulated using one set of input parameters. Key features in the voltage and temperature profiles are explained by looking at the simulated state inside the stack.Li-ion cells are now well established for use in applications which require high currents, such as power tools, e-bikes and various varieties of the HEV. For these applications, the cell design engineer must pay careful attention to the cell impedance for any proposed cell design. However, the estimation of cell impedance is a vastly more complex issue than is the calculation of cell capacity. In fact, the notion of cell impedance is not even a well defined concept. What is really required is the calculation of voltage curves at high currents in the presence of self heating.Accurately predicting the dynamic cell response for a wide range of applied currents, ambient temperatures and cell designs is nontrivial. The original work in this direction 1 achieved good results up to about a 2C rate, at ambient temperature, for a graphite/Li Mn 2 O 4 Li-ion cell. More recent work 2 focused on simultaneous simulation of three cell designs with various electrode thicknesses, and numerous electrolyte salt concentrations. Again, the simulation results deviate significantly from the cell data for discharge rates > 2C. These authors found it necessary to modify the salt or solid phase diffusion coefficients, as a function of discharge rate, in order to accurately reproduce the observed voltage profiles. Further studies which include self heating effects 3,4 have similar issues with high currents. None of these researchers had access to recently measured 5-8 electrolyte transport properties and salt activity. At a minimum, the temperature and concentration dependence of the salt diffusion must play an important role when self heating takes place. Other work has shown simulations of HEV pulse profiles 9 with 4C pulses lasting 18 seconds wherein the short duration of the pulses did enable a rather good agreement with experiment using the isothermal model. Pulses up to 10C were simulated using a full electro-thermal coupled model in reference 10 including some comparisons with experimental data at 0 • C. The authors observed some disagreement at 5C and 10C rates at 0 • C, but obtained remarkably good results for full 10C discharges at 25 • C without optimizing the model parameters. Reference 1...
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