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Single-layered pouch-type cells were exposed to quasi-isothermal external short circuit tests to study the influence of electrode loading and tab configuration on the short circuit characteristics. Additionally, test conditions such as initial cell temperature, cell voltage and external short circuit resistance were varied. Keeping the cell's temperature increase below 1 • C whilst using a calibrated calorimetric setup, a direct correlation between the electrical and thermal behavior could be shown without occurring exothermal side reactions. Previously studied step-like characteristics in the transient current profile could be confirmed for all cells and test conditions, showing differing durations and magnitudes of the observed plateaus based on ohmic resistances, transport processes and reaction kinetics. Lower electrode loadings, counter-tab configurations homogenizing the current density distribution and higher initial cell temperatures accelerate the short circuit by increasing the cell current due to a reduced effective cell resistance. Whilst the chosen initial cell voltages and external short circuit resistances showed a minor impact on the short circuit dynamics, the initial state of charge revealed a noticeable influence defining the discharged capacity and the amount of generated heat. By post mortem analysis, the observed over-discharge could be correlated to an anodic dissolution of the negative electrode's copper current collector.

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Measurement data gained from quasi-isothermal external short circuit tests on single-layered pouch-type Li-ion cells presented in the first part of this combined work was used to validate a well-known homogenized physical-chemical model for different electrode loadings, cell temperatures, initial cell voltages, and external short circuit resistances. Accounting for diffusion-limited reaction kinetics, effective solid phase diffusion coefficients, and one representative active material particle size within each electrode, the model is capable of describing the experimentally observed characteristic change in magnitudes of current and heat generation rate throughout the short circuit. Underlying mechanisms for the observed characteristics are studied by evaluating the predicted concentration distribution across the electrodes and separator and by calculating the cell polarization due to ohmic losses, diffusion processes, and reaction kinetics. The importance of mass transport in the solid and liquid phase limiting reaction kinetics is discussed and evaluated in the context of a sensitivity analysis. Concentration dependent transport properties, electrode tortuosity, particle size, and electrode energy density are affecting different stages of a short circuit. Simulation results suggest a strong impact of electrode design on the short circuit dynamics allowing for an optimization regarding a cell's energy and power characteristics whilst guaranteeing a high short circuit tolerance.

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