| Improved battery technology will aid the electrification of vehicles, leading to better efficiency and substitution of energy from the grid (which may come from many sources) for oil. We developed models and conducted experiments to aid in the understanding and optimization of the nickel metal hydride (Ni/MH) and several lithium-ion chemistries. Fundamental equations from transport, thermodynamics, and kinetics were used to model the cell sandwich.;For the Ni/MH chemistry we focused on the oxygen and hydrogen side reactions and nonisothermal effects and compared our model with the potential, temperature, and internal pressure of a Toyota Prius module. We constructed an optimized Ragone plot, and found that the Ni/MH performance is adequate for hybrid-electric vehicles but insufficient for electric vehicles. Capacity loss at the MH electrode during aging can increase hydrogen generation during charge.;We studied the relationships among cell chemistry, battery size, and capacity use, focusing on the magnitude and shape of the pulse-power capability and the cell energy. We found that a high pulse-power capability and cell energy reduce battery size and increase capacity use, as does a flat pulse-power capability. A flat pulse-power capability results from a flat cell equilibrium potential when the current distribution is uniform, but for a nonuniform current distribution a sloped pulse-power capability results because solid-phase concentration gradients through the electrode depth do not relax.;We modeled cells with a positive electrode composed of multiple types of active materials and compared model results with constant- and alternating-current experimental results. We included multiple types of connections between the electrochemical reaction sites and the conductive solid matrix to obtain a good match between simulations and experiments. For some lithium-ion chemistries the use of multiple active materials may improve lifetime and performance, and assist with start-of-charge determination.;Finally, we completed a study on aging of lithium-ion cells. Cells were held at a variety of temperatures and potentials, and full-cell electrochemical tests and postmortem tests, such as making coin cells from harvested electrodes, were conducted. We identified the principal cause of aging as a shift in the capacity balance due to reduction reactions at the negative electrode. |
